Astronomy & Geophysics

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty103

View largeDownload slide View largeDownload slide MARS April marked some milestones for the exploration of Mars: the ESA/Roscosmos ExoMars orbiter sent back its first pictures of Mars from a near-circular 400 km-altitude orbit, while NASA and ESA signed an agreement to work together to explore the possibilities for returning martian samples to Earth. ESA's director of human and robotic exploration, David Parker, and NASA's associate administrator for the science mission directorate, Thomas Zurbuchen, signed the statement of intent on 26 April at the ILA Berlin Air Show. Sample-return from Mars is a complex undertaking, not only in sample selection, as Mark Sephton outlined in the February 2018 issue (A&G 2018 59 1.36), but also in the coordination of three spacecraft, two landings and a launch from Mars. One element is already in place: NASA's 2020 Mars rover will collect and store samples in preparation for a possible future mission to collect them. In a sign of the potential for collaboration, the ExoMars orbiter has already transmitted data from NASA's Curiosity rover back to Earth, adding to the martian communications infrastructure. A prime role of this orbiter, however, is to investigate the atmospheric composition of Mars, its methane in particular. The Trace Gas Orbiter's Colour and Stereo Surface Imaging System, CaSSIS, took this spectacular image of Korolev crater, at high northern latitudes. “We were really pleased to see how good this picture was, given the lighting conditions,” said Antoine Pommerol, a member of the CaSSIS team working on the calibration of the data. “It shows that CaSSIS can make a major contribution to studies of the carbon dioxide and water cycles on Mars.” TGO also carries two spectrometer suites and a neutron detector. In this orientation, north is off-centre to the upper left. (ESA/Roscosmos/CaSSIS) http://bit.ly/2dOD8EO © 2018 Royal Astronomical Society

Bowler, Sue

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty144

The National Astronomy Meeting, UK Solar Physics Meeting and the European Week of Astronomy and Space Science came together for a big and busy meeting in Liverpool. Sue Bowler reports. A packed programme of specialist and plenary sessions, public events and a conference dinner in the spectacular setting of Liverpool Cathedral made for an exciting, if exhausting, week in early April. Joining forces with the European Astronomy Society gave a welcome European flavour, with addresses from the leaders of major European organizations as well as UK agencies. There was also a strong African theme, with sessions on international research and astronomy for development. At the UK-focused community session, Mark Thomson, newly appointed executive chair of the Science and Technology Facilities Council, began by setting out two goals. First comes the need for STFC to get more funding for research and development (R&D) in the 2018/19 budget. Second, there is the aspiration to move towards the UK putting 2.4% of gross domestic product into R&D by 2027. He noted that overall funding for R&D has been increasing, with directed government support for the Global Challenges Research Fund (GCRF) and the Industrial Strategy Challenge Fund (ISCF), plus infrastructure and training investment. “The message is that the government understands the value of science and technology for the economy,” he said. However, continued flat cash allocations for core funding means that STFC is facing a ∼£12.3m resource gap, with the prospect of a £17.6m capital gap by 2020/21 unless something changes. The programme is surviving, but Thomson made it clear that continued flat cash settlements will reduce the breadth of the programme on a 5–10-year timescale – and the resources available to support new ideas will be seriously squeezed. This will mean cancellations of programmes and new projects going unfunded. The onus is on the astronomical community to get more funds through UK Research and Innovation (UKRI), now the overarching research body, including from directed research funds such as the GCRF, and to make the most of new opportunities such as the Future Leaders Fellowships. Thomson concluded with an appeal to the community to give STFC the information it needs to make the case for better funding for core science. “The Department for Business, Energy and Industrial Strategy, and UKRI, understand the pressure on the STFC core programme, but we have to argue better. Simply saying ‘we need more money for our core programme’ may be true, but it won't do. We have to make clear arguments about the impact of flat cash: the narrowing of our programme, the loss of opportunities and the fact that, if we lose out at the core, we will not be able to deliver innovation.” Chris Lee, head of space science at the UK Space Agency, was also new to his role. He introduced himself by noting that, while most people in his business grew up wanting to be an astronaut, he had wanted to be an astronomer, so he felt very much at home at the meeting. The UKSA employs 140 people, with a budget of £500m per annum; Lee manages a budget close to £100m (including ESA). His goals are to make the most of the mandatory ESA funding, showcase UK innovation built on space science and to be inspirational, especially for children, but also for adults, who pay taxes. He sees the future in terms of bilateral partnerships with countries such as India, China and Chile, and a focus on instruments and scientific research, adding value to UK research. There are opportunities in the near future; it is possible that the ESA Council of Ministers meeting in 2019 will decide to put a larger fraction of its funding into space science. View largeDownload slide View largeDownload slide Lee also hopes for more joined-up thinking for UKSA and STFC and in areas such as infrastructure investment, despite UKSA not being part of UKRI. He sees the increasing importance of directed funding from the GCRF and ISCF as potentially positive. “Internationally, space science is seen as necessary for sustainable devleopment,” said Lee, “and the UK is seen as a leader in education worldwide.” He too sought input from the community. Connie Aerts of the Institute of Astronomy, KU Leuven, then addressed the meeting to stress the value of bottom-up community advice, but made the point that the community is more than just the scientists. Teachers and especially parents are also very important, among the general public who need to be on-side for science. And working from the bottom up makes an immediate – and often very much needed – difference to the diversity of people and opinions involved. Questions for all speakers from the floor revolved around two issues: Brexit and the future of European funding for UK researchers, and funding in general. Thomson stressed his view that UKRI meant there was a strong voice to government on behalf of UK research – and on Brexit as well. He felt that the government appreciated the importance of European funding to UK science, although how that would fit into overall priorities in Brexit remains unknown. Several questioners addressed the problem of STFC making a good case for fundamental research and the links to societal and economic impact. RAS President John Zarnecki made the point that this community is driven by intellectual curiosity; Thomson responded that STFC's core programme is curiosity, and if we want more funding, we have to demonstrate an increase in the results for the economy. So, that's the challenge for the astronomical community: to provide examples, figures and facts that show that cutting-edge science drives innovation. European perspectives EWASS included presentations from the leadership of ESA, the European Southern Observatory and the Square Kilometre Array. Xavier Barcons, ESO director, began by setting the scene for this €300m-budget organization with 700-plus staff. ESO is looking forward to welcoming Ireland, who will be joining ESO as the 16th member this year. Australia has agreed a partnership with La Silla and Paranal, although Brazil's application for membership has stalled. ESO is a research powerhouse, with ESO research featuring in more than 1000 papers in 2017, 30% of which used archive data. Instrument development was continuing, including the first combination of light from the four VLT telescopes to the ESPRESSO spectrometer in February 2018, resulting in an effective 16 m mirror and the same signal-to-noise ratio in one hour's observation as achieved by HARPS in a day. On shared facilities such as ALMA, where ESO has a 37.5% share, 42% of the 1000 papers published since 2013 were led by European researchers – a very good return on investment. The Extremely Large Telescope looms appropriately large in ESO's plans. The programme is 94% funded, with full funding for the main mirror, which will be built as a disc, not a doughnut; the largest telescope will thus have the largest mirror. “The project is within budget and within schedule,” said Barcons. “We have gone past the paperwork stage.” He concluded with his vision for the next decade: “The current challenge is to deliver the ELT, the first and most powerful telescope of its class, while keeping our other observatories active and powerful. We can think about new projects, but not for the next five years.” Günther Hasinger, science director of ESA since February, gave his presentation remotely – and very successfully. He began by stressing the value of ESA's structure and support. “We've benefited greatly over the past 10–15 years from the financial stability offered by our member states. It's really our backbone.” He outlined past and current successes, noting the selection of M4 mission ARIEL, for exoplanet spectroscopy, to be followed by Athena, for high-energy astrophysics, and LISA, to explore gravitational waves. But he also stressed the need to plan ahead, noting that asteroids and the ice giants represent gaps in the ESA programme. Bringing light to LIGO was also a priority and ESA was considering exploiting the synergy between LISA and Athena, for example, to track down primordial black holes, by flying these two missions at the same time. 1 View largeDownload slide Winners of the 2018 RAS medals and awards received their prizes at the conference dinner, held this year in the spectacular Liverpool Cathedral. Pictured are the host, comedian Jon Culshaw, RAS President John Zarnecki, and the Patrick Moore medal winner, teacher Jenny Lister. (RAS/N Cole) 1 View largeDownload slide Winners of the 2018 RAS medals and awards received their prizes at the conference dinner, held this year in the spectacular Liverpool Cathedral. Pictured are the host, comedian Jon Culshaw, RAS President John Zarnecki, and the Patrick Moore medal winner, teacher Jenny Lister. (RAS/N Cole) The strategy Hasinger outlined for Cosmic Visions until 2050 was to strengthen ESA science at all levels, with concomitant outreach and educational activities. He hopes for a 20% increase to allow LISA and Athena to fly together, and plans to propose a new M mission to Uranus and Neptune, possibly in cooperation with NASA to exploit a fortuitous planetary alignment. These positive, forward-looking international views of science were complemented by the third speaker of the morning, Philip Diamond, director of the Square Kilometre Array, who aligned the SKA alongside – and complementary to – other 21st-century observatories, including Athena and the Cherenkov Telescope Array (starting work in 2024). Diamond emphasized that SKA had the broadest range of key science drivers: “SKA addresses the whole history of the universe and exploration of the unknown, and much of the science is fundamental physics.” To give an idea of the scope of the project, he noted that we now know of about 2000 pulsars; SKA will detect ∼30 000 in the Milky Way. Phase 1 of the project will support gravitational wave discoveries, phase 2 will do gravitational wave astronomy. Diamond summarized the progress of the SKA Observatory, comprising three sites, two telescopes and the headquarters, plus ∼600 scientists and engineers. This is the final year of the design phase; the HQ at Jodrell Bank is nearing completion and progress towards establishment of the treaty organization continues. The SKAO is expected to be operational by 2020. A date with diversity Sheila Kanai, RAS Diversity Officer, gives an overview of the EWASS–NAM 2018 focus on diversity in astronomy. For the first time in NAM history, diversity and equity was the focus for a whole day. The session was organized by partners across Europe, including chairs Helen Jermak from Liverpool John Moores University, and Sara Lucatello from Observatory of Padova, Italy; we acknowledge welcome sponsorship from Nature Astronomy. The day began with unconscious bias training, followed by a panel discussion on the barriers and challenges women face. The lunchtime plenary included UK MP Chi Onwurah speaking on women in STEM, including Caroline Herschel and excellent role models from black, Asian and minority ethnic backgrounds. In the afternoon, talks and discussions spanned every aspect of diversity from Asperger's syndrome to visual impairment. Robert Massey of the RAS presented the results of our demographic survey. Racial inequality in Africa was examined, as were the trials and tribulations of being a trans woman in astronomy. Topics such as sexual harassment and bullying led to an impassioned and emotional panel discussion. A particularly moving moment was the rapturous applause for Kate Furnell from Liverpool John Moores University, who spoke so candidly about her mental health during her time as a PhD student. 2 View largeDownload slide Chi Onwurah MP. 2 View largeDownload slide Chi Onwurah MP. As diversity officer at the RAS, I feel this is just the beginning for us. The demographic survey highlighted areas that the RAS needs to work on, showing us the gaps in diversity and equity that need to be filled. Hearing first hand from inspirational speakers gives us a glimpse into their world, and highlights what the RAS and the astronomy and geophysics community need to do to become more diverse and inclusive. The day concluded with a debate about harassment and bullying and what the RAS is doing to support Fellows. There are still many questions to answer, but at least a dialogue has begun. I feel that the RAS is very well placed to support Fellows and the wider communities. http://bit.ly/2KsKgCd MORE INFORMATION The joint NAM–EWASS–UKSP meeting was held on 3–6 April 2018 in Liverpool. Conference website: http://eas.unige.ch/EWASS2018 © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty104

View largeDownload slide View largeDownload slide RAS A portrait of William Pearson, which will be familiar to many members of the RAS from the Fellows' Room, has been conserved, possibly for the first time since it was painted by Arthur Phillips in 1808. In this, the best known portrait of Pearson, one of the founders of the RAS (A&G 2017 58 5.12), he is portrayed pointing out one of his planetary machines to his first wife Frances, and his only daughter, also Frances. The orrery in the painting has sadly not survived. The portrait was cleaned and revarnished, giving fuller saturation to the colours. Essential remedial treatment was carried out on the frame, and low-reflection UV protection glazing was installed, so that the newly revived colours of this family portrait will be preserved for the future. © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty099

POLICY UK Research and Innovation came into being at the start of April this year, uniting all seven Research Councils together with Innovate UK and a new body, Research England. At the same time, Mark Thomson took over as CEO of the Science and Technology Facilities Council. View largeDownload slide “UKRI is a major opportunity” – Mark Thomson, CEO STFC. (Univ. Cambridge) View largeDownload slide “UKRI is a major opportunity” – Mark Thomson, CEO STFC. (Univ. Cambridge) UKRI describes itself as an independent body providing a strong voice for research and innovation. A key role for such a body – principally funded through the science budget by the Department for Business, Energy and Industrial Strategy – is to boost the connections that support research, between government, researchers, business and the public. The overarching goals are to deliver impact in knowledge and understanding, economic benefit and in society and culture, in the UK and abroad. How they will achieve this will be set out in a UKRI strategy and corporate plan. Mark Thomson welcomed UKRI as an opportunity, for STFC and for academics. His background is in experimental particle astrophysics, most recently with the DUNE experiment, which received £65m of direct government investment in 2017, to be part of a major US-led collaboration. “I see UKRI as a major opportunity,” he said, speaking at the National Astronomy Meeting in Liverpool this year. “It's a unified voice for research and innovation, that can go to government and make our case. We in turn can be more strategic and work across research councils and across subjects to tackle new challenges. And it provides a smoother path for innovation.” UKRIhttp://www.ukri.org Thomsonhttp://bit.ly/2w4ptBJ © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty119

SPACE JUNK ESA is modelling what happens when satellites collide – and finding surprises. Only one out of four model collisions produced the cloud of space debris expected. Engineers are using two types of model, working at the levels of the material properties and the components of satellites under the high energies of collision. The goal is to help predict how Earth's cloud of space junk will evolve over the coming 200 years. http://bit.ly/2rfrWUp © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty118

TESS NASA's Transiting Exoplanet Survey Satellite (TESS), was launched on 18 April and is heading for its final elliptical 13.7-day orbit with the help of six thruster burns and a gravity assist from the Moon. TESS will survey 85% of the sky, looking for transits on bright stars between 30 and 300 light-years away. These stars will be candidates for follow-up spectroscopy. TESS is expected to discover thousands of exoplanets, among them some 300 Earths and super-Earths. http://go.nasa.gov/2FzoKYI © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty128

GALAXY EXPANSION Our galaxy is probably growing – but slowly, getting bigger by about 500 m every second. The growth comes from starbirth in the outer parts of the disc, according to Cristina Martínez-Lombilla (Instituto de Astrofísica de Canarias in Tenerife) and collaborators. They combined optical data from the Sloan Digital Sky Survey, ultraviolet data from GALEX and infrared data from the Spitzer Space Tele-scope to identify young stars in spiral galaxies like our own. They measured the stars' velocities and calculated how quickly they were moving apart and thus how quickly the galaxies would grow. http://bit.ly/2JEGiFk © 2018 Royal Astronomical Society

Evans, Wyn

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty143

An appreciation of a giant of 20th-century astrophysics by Wyn Evans. View largeDownload slide View largeDownload slide Donald did not lecture in the modern way. I attended his graduate course on Galaxies in 1984–85, at the University of Cambridge. The lectures were chaotic and stimulating. Chaotic, because Donald would always work out formulae from first principles and without notes on the blackboard. This had the advantage that mistakes in chalk could be quickly erased, sign changes corrected. It also gave us students enormous insight into how to develop ideas into theory and how to catch errors as you made them (or at least shortly after making them). Stimulating, because his lectures were always intensely personal. If lecturing on, say, dark matter in dwarf galaxies, Donald would discuss whether he believed the data or whether he trusted the theoretical analysis. We were shown the building site – the place where the work was done, where a first-rate mind questioned, analysed and teased the data or theory. He showed us how to think, not what to learn for the exam. The exam was characteristically intractable. Donald did not supervise students in the modern way. I was his student for three years from 1985–88, and at no point was I actually working on a well-defined project. Rather, Donald was interested in … oh, pretty much everything astronomical, from general relativity to stellar dynamics to large-scale structure to stellar evolution to optical instruments. Donald's students were free to see him any time to talk about things he was interested in. Nominally, this weekly meeting took an hour, but in practice, if his imagination was fired up, the session might last all morning or afternoon. He posed problem after problem, and we would attempt to answer the problems together on the blackboard in his office. Usually, we students would emerge hours later, covered in chalk and sapped of all energy reserves. If unlucky, we had missed lunch. But Donald was always still perky and fresh for more problems after a session with a graduate student. Astronomy on the brain Donald never stopped thinking about astronomy. As a grad student, I wondered how he relaxed. I remember talking to him about movies. “The only movies I've seen in 20 years are N-body movies,” he said. Other things Donald seemed to have no interest in included departmental politics, gossip, fiction, fine food and drink. Those meetings in his office in the Observatory, room O2, were some of the most vivid encounters of my life. “The star's motion is like a slippery grape in a rotating fruit bowl,” he would cry. And off we would go, writing down the equations in chalk on the board, correcting the sign of the Coriolis term as we went, trying substitutions and transformations to make the equations tractable and solvable. There would always come a time when I wanted to stop, the board was densely covered in chalk and scrawl, some equations were partly rubbed out, some equations were probably not even correct, maybe it made sense to write it down on paper now. But Donald never wanted to stop, his energy was inexhaustible. At times, out of his battered brown briefcase would come enormous, ledger-sized books with various problems in different states of working, sometimes labelled with the name of the poser. One impressive volume was called “Roberto's Problem”, though I never actually learnt what that was. Another was “Alar's Problem” (the change in adiabatic invariant after separatrix crossing). Here, the eponymous Toomre had solved the problem, but had thoughtfully sealed his envelope containing the solution with lots of sticky tape to prevent Donald from peeking. Of course, Donald wanted to solve it himself. Donald knew a lot of mathematics, including some subjects no longer familiarly taught in undergraduate courses. But he never appreciated purely mathematical arguments. He always argued for the primacy of physical insight. I remember introducing him to Vladimir Arnold's Mathematical Methods of Classical Mechanics, a beautiful and splendid cathedral of differential geometry erected over Hamiltonian mechanics. “Not as good as Whittaker,” he said, referring to one of his favourite books, Whittaker's impenetrable late-Edwardian Analytical Dynamics. “Whittaker shows you the gaps.” For Donald, a good book was one that was incomplete in its argument and ragged in its exposition – because that stimulated further thinking and research. Of course, Donald loved Arthur Stanley Eddington's books more than anything else. His inscrutable and earnest face looked down from Donald's office wall. Any modern book on relativity or stellar structure or dynamics was “not a patch on Eddington”. Donald loved seminars, and he loved asking questions. Many is the time I have seen a speaker, arguments all polished and shining, thrown by an awkward question from Donald. He had a booming voice, and often an unusual perspective on a theoretical problem or on observational data, and so the question could come fast and unexpectedly to the speaker from left-field. Donald did not restrict himself to subjects in which he had done research. His mastery over astronomy was so great that he could devise a fiendish question in any area. But, he never asked to bamboozle the speaker, he asked because he was playfully and inexhaustibly curious. In astronomy, Donald often had the greatest respect for individuals who did things he couldn't do himself, such as instrument building (Roger Angel), or pioneering N-body simulations (Sverre Aarseth and Simon White) or stellar evolution codes (Peter Eggleton). Golden period Donald completed his PhD under the supervision of the late Leon Mestel in 1960. His thesis laid the foundations for Donald's golden period, an incredibly productive decade-and-a-half in which glorious paper followed glorious paper. The finest achievements include solo papers in 1962, which derive exact solutions for steady-state elliptical galaxies and which systematically study the potentials that can support triaxial stellar systems; two fundamental papers with Peter Goldreich in 1965, which led to the discovery of swing amplification, the mechanism that drives spiral structure in galaxies; an important paper with Jim Pringle in 1974, which lays the foundations for the evolution of accretion discs around the “nebular variables” or T Tauri stars and predicts the signature of excess infrared emission. In 1968, puzzled by work sent to him from Leningrad by Vadim Antonov, Donald rediscovered the gravothermal catastrophe and comprehended its implication for the evolution of the globular clusters. This awakened his interest in negative heat capacities, a research subject he subsequently pursued with his wife, Ruth Lynden-Bell (professor of chemistry at Queen's University, Belfast). His theoretical papers, often staunchly mathematical, were relieved with humour and analogies, such as Donald's Demon who impishly reverses the velocities of stars. “It's important that observers read them too,” he often said. And then in 1969 came the Nature paper – Donald's single most important contribution – which hypothesized the existence of supermassive black holes, or dead quasars, at the very centres of galaxies. Years later, in 2008, this heart-stopper of a paper would win Donald the inaugural Kavli Prize, shared with Maarten Schmidt. This splendid flowering of theoretical astrophysics gave way to increasing interest in the observations in the 1980s and 1990s. Donald joined forces with six other warriors to form the Seven Samurai. Devising new distance estimators, the Samurai analysed the local flows of galaxies and discovered the Great Attractor, an enormously massive agglomeration into which most of the nearby galaxies are falling. In the Milky Way, Donald was the first to recognize the great future of tidal streams, both as measures of the gravity field and as evidence of the hierarchical accretion that builds up the galaxies. This was bittersweet, as merging and accretion had gradually displaced the older picture of collapse that Donald had himself devised with Olin Eggen and Allan Sandage in a highly cited and influential paper in 1962. They used evidence from chemistry and kinematics of local halo stars to suggest that our galaxy had collapsed from a single large gas cloud. Though this idea has not survived, the lineal descendants of Donald's paper are all around us today in the wide-field spectroscopic and multi-band photometric surveys of the galaxy. Donald loved the Royal Astronomical Society and its even older sibling, the RAS Dining Club. He regarded the Presidency of the RAS as a high honour and was proud of his service from 1985–87. He viewed the RAS as playing a hugely important role in fostering interest in, and support for, astronomy for two centuries. Star Men Donald remained mentally vigorous almost to the very end. His interests in recent years had become focused on fundamental questions as to the origin of Mach's Principle and the localization of energy in general relativity. He was still regularly attending morning coffee and seminars at the Institute of Astronomy right up to his final illness, still bounding up to grad students and asking, “What are you working on?”, before explaining excitedly to them what he was working on. He was still taking the pen, ever ready to scribble equations on the whiteboards over coffee. He was still smilingly curious. His collaboration with Alison Rose led to the graceful Star Men movie about his recreated journey to Rainbow Bridge, Utah, accompanied by Wal Sargent, Nick Woolf and Roger Griffin, together with meditations on science, life, hiking and ageing. But to me, Donald never aged. He was immutable. He always looked the same as he did when I was his grad student in the late 1980s. Some people you really think will be there for ever… © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty131

DARK ENERGY SURVEY A survey has found 72 very bright, very fast and really quite odd transient stars. They look like supernovae, but don't match any model. The data come from the Dark Energy Survey, which includes a supernova search. Miika Pursiainen (University of Southampton) noted that the transients are as bright as some supernovae, but fade faster, lasting weeks rather than months. They are hot, 10 000–30 000 K, and big, from a few to ∼100 au. Their light curves suggest that they cool and expand as they age, consistent with an explosive origin. The signals could come from a cloud of ejected matter, not the star itself. http://bit.ly/2FwRIse © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty105

View largeDownload slide View largeDownload slide NEOWISE NASA has released four years of data from its Near-Earth Object Wide-field Survey Explorer (NEOWISE) spacecraft. The data include 788 near-Earth objects and 136 comets found since the mission restart in 2013. NEOWISE was originally the astrophysics mission WISE, which finished in 2011; the repurposed spacecraft tracks near-Earth asteroids and characterizes more distant populations of asteroids and comets. It detected 29 246 objects in four years. The image represents the solar system in December 2017: main-belt asteroids (grey), near-Earth asteroids (green), comets (yellow), objects discovered in final week (white), Earth's orbit (cyan), and other terrestrial planet orbits (blue). (NASA/JPL-Caltech/PSI) http://bit.ly/1RpHbln © 2018 Royal Astronomical Society

Watson, Fred;Urquhart, Jane

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty147

It's all change for the Australian Astronomical Observatory – Fred Watson and Jane Urquhart explain what is happening to this astronomical powerhouse. It's hard to think of a time when the landscape of Australian astronomy was changing as rapidly as it is at present. Perhaps during the pioneering days of radio astronomy following the second world war? Or in those heady days, three decades later, when optical astronomy was revitalized by the Anglo-Australian Telescope (figure 1)? Today, radio astronomy in Australia maintains a steady-as-she-goes approach, with innovative new facilities paving the way for the Square Kilometre Array in the 2020s. But the optical community is undergoing epochal transformation – bringing both opportunities and challenges. 1 View largeDownload slide Siding Spring Observatory is dominated by the dome of the 3.9 m Anglo-Australian Telescope (centre). On the extreme left is the 1.3 m ANU SkyMapper Telescope, while the 1.2 m UK Schmidt Telescope and Las Cumbres Observatory 2 m Telescope are on the right. (ANU) 1 View largeDownload slide Siding Spring Observatory is dominated by the dome of the 3.9 m Anglo-Australian Telescope (centre). On the extreme left is the 1.3 m ANU SkyMapper Telescope, while the 1.2 m UK Schmidt Telescope and Las Cumbres Observatory 2 m Telescope are on the right. (ANU) At the heart of the changes is infrastructure – which, for astronomers, of course, means telescopes and instrumentation. Being a well-organized cohort, Australian astronomers carefully review all aspects of their science on a decadal basis, incorporating the results into a formal planning document. Thus they can stocktake their inventory of facilities and spell out their aspirations with cogent scientific arguments to support them. And successive decadal plans for Australian astronomy – including the current one, Australia in the Era of Global Astronomy, 2016–2025 (Australian Academy of Science 2015) – have highlighted the need for significant amounts of time on optical telescopes in the 8 m class. Looking to Europe In recent years, such access has been granted by relatively short-term financial agreements with overseas institutions. While they have been scientifically productive, these arrangements have provided little opportunity to influence the design and procurement of advanced instrumentation for the telescopes, an area in which Australia has particular expertise. So it is no secret that Australian astronomers have long coveted the idea of the nation being affiliated with ESO, the European Southern Observatory. Of course, ESO membership involves significant cost, which demands high-level government support. A near-success two decades or so ago fell victim to budget pressures in the run-up to the 1996 federal election, relegating the issue to a fond hope in the bosoms of optical astronomers in Australia and Europe. But recently, with almost breathtaking swiftness, there has been a shift in the fortunes of those ambitions. Rumours of behind-the-scenes negotiation gave way to a blaze of publicity at the Astronomical Society of Australia's 2017 Annual Scientific Meeting in Canberra. There, on 11 July, a 10-year strategic partnership was inaugurated by senator the Hon. Arthur Sinodinos, then Commonwealth minister for industry, innovation and science, and Tim de Zeeuw, then ESO director general (figure 2). 2 View largeDownload slide An historic day for Australian astronomy: the minister for industry, innovation and science Arthur Sinodinos, and the director general of ESO Tim de Zeeuw, sign the partnership agreement between Australia and ESO in July 2017. (DIIS) 2 View largeDownload slide An historic day for Australian astronomy: the minister for industry, innovation and science Arthur Sinodinos, and the director general of ESO Tim de Zeeuw, sign the partnership agreement between Australia and ESO in July 2017. (DIIS) Although this arrangement does not constitute full Australian membership of ESO (which current fiscal realities prohibit), it does provide long-term access to the world's most comprehensive suite of optical astronomy facilities at La Silla and Cerro Paranal in northern Chile. The ability to use the four 8.2 m Unit Telescopes of ESO's VLT at Paranal (figure 3) is an important prize for Australian astronomers, fulfilling the critical requirement for this class of instrument. The new deal also explicitly aims to capitalize on Australian know-how in instrumentation, with promised benefits for domestic universities and industry. 3 View largeDownload slide A sunset portrait of the four 8.2 m Unit Telescopes of ESO's VLT at Paranal. (J C Muñoz-Mateos) 3 View largeDownload slide A sunset portrait of the four 8.2 m Unit Telescopes of ESO's VLT at Paranal. (J C Muñoz-Mateos) Technology is only one of the reasons ESO is keen on Australian involvement, however. Successive decadal plans have highlighted the high-impact science carried out by Australian astronomers, whose contribution can only be enhanced by the new facilities now becoming accessible. These facilities were warmly embraced by Australian astronomers during the first round of ESO telescope time applications available to them. This was for period 101, whose closing date was a mere two-and-a-half months after the partnership was signed into existence. No fewer than 55 Australian-led proposals were submitted by 160 astronomers from 16 Australian institutions – 6% of all the proposals – reflecting, perhaps, a long pent-up demand on the part of the Australian community. Excluded from the new partnership is ESO's Atacama Large Millimetre Array (ALMA) at the Llano de Chajnantor site near San Pedro de Atacama. Access to this 5100 m altitude submillimetre facility has lower priority for Australian astronomers than use of the 8 m class optical telescopes. Likewise, ESO's 39.3 m Extremely Large Telescope (ELT), currently under construction at Cerro Armazones (near Paranal), is excluded. Until the conclusion of the strategic partnership in 2027, however, Australia will have the opportunity to enter into full membership of ESO, with access to both ALMA and ELT. While it is difficult to chart the financial landscape that will then prevail, there is optimism that this will be a real possibility. The other side of the coin The government's initiative in forging the partnership with ESO has been widely praised within the Australian astronomical community. The concomitant change, however – which, at the time of writing, is in the final stages of formulation – heralds the biggest makeover in the 44-year history of the Australian Astronomical Observatory (AAO). Until 2010, AAO was the Anglo-Australian Observatory, a UK–Australian institution with joint funding that was frequently held up as an exemplary international collaboration. Following the UK's withdrawal from the agreement in 2010, the observatory became a division of the Australian government's science department, which is today the Department of Industry, Innovation and Science (DIIS). That metamorphosis left the key functions of the old AAO intact; namely, operation of the 3.9 m Anglo-Australian Telescope (AAT) and 1.2 m UK Schmidt Telescope (UKST) at Siding Spring Observatory near Coonabarabran, and the observatory's technology and facilities base in Sydney. Some readers will recall with affection the AAO's somewhat ramshackle Sydney offices in the leafy northern suburb of Epping. In 2012, however, a move was made to new purpose-built premises in North Ryde – no less leafy by virtue of nearby parkland (and the Northern Suburbs Crematorium), but lacking the soul of the Epping lab. The advent of Australia's partnership with ESO draws a line under this chapter in the AAO's history, and the old operating model will come to an end on 30 June 2018. What will replace it is a move from the government to the research sector, with the Coonabarabran and Sydney operations falling under two different university consortia. Once again, it is fiscal reality that dictates the need for this transformation. Without it, the observatory's finances would have cascaded over a precipitous funding cliff in 2020. With it, the requirements of the decadal plan in maintaining the key functions of the AAO until at least the mid-2020s can be met. The new model for the AAO's facilities places the operation of the AAT under the management of Astronomy Australia Ltd (AAL), a not-for-profit company whose members are Australian universities and research organizations with significant astronomical research capabilities. Founded in 2007 to manage collaborative research infrastructure grants in astronomy, AAL remains an advocate for Australian astronomy facilities. From 1 July 2018, the Commonwealth will lease the premises exclusively to the Australian National University (ANU), acting on behalf of a consortium of 13 fee-paying Australian universities. The ANU already owns and operates Siding Spring Observatory on which the AAT is located, and has several of its own staff there as well as staff from other institutions with facilities on the site. The AAT Consortium agreement will cover the operation of the telescope for seven years; funds for the first four are already committed. While the telescope will continue to be the property of DIIS, its governance will be through a new AAT Council, whose membership will be drawn from the AAT Consortium and AAL. The majority of its staff will become ANU personnel. The allocation of time on the AAT (figure 4) will continue more or less as at present, with an independent panel determining the programmes to be supported in each semester. The telescope will continue to be a national facility, available for cost-free use by astronomers at any Australian institution. A new category of paid time for non-Australian proposals, or proposals from Australian teams wishing to guarantee access, will also be formalized. (Astronomers interested in AAT paid time should contact AAL for more information: info@astronomyaustralia.org.au.) Enthusiasm for observations using the AAT with its outstanding suite of instruments has not waned throughout the transition process: applications for time in semester 18B (Aug 2018 – Jan 2019) reflected the normal oversubscription rate of two to three times the available nights. 4 View largeDownload slide The 3.9 m Anglo-Australian Telescope, opened in 1974. (Á López-Sánchez) 4 View largeDownload slide The 3.9 m Anglo-Australian Telescope, opened in 1974. (Á López-Sánchez) New surveys for UKST The situation for the UKST is rather different. Despite being operated by AAO since 1988, it has been owned by the ANU since the transition of 2010. As described later in this article, two new large-scale surveys (Taipan and FunnelWeb) will take up all available time on the telescope. So much for the telescopes – what of the AAO's facilities in Sydney? Once again, the importance of the observatory's world-class instrumentation programme is highlighted in the decadal plan, and it will continue into the new era. Towards the end of 2017, several Australian institutions responded to a DIIS invitation for expressions of interest to host the AAO's science and technology groups. The successful bid came from a consortium led by Macquarie University and including the ANU and the University of Sydney, with funding primarily through AAL in partnership with the universities. All three of the universities involved have a history of innovative instrumentation research, frequently in collaboration with AAO. At the time of writing, negotiations are still proceeding on details of the transfer to Macquarie University. In terms of the physical location of the AAO's Sydney group, it is likely that the North Ryde premises will be retained until new purpose-built accommodation is constructed on the Macquarie campus, some 4 km away. But it is also expected that the unity of the group will be retained within Macquarie University in order to preserve the internationally known AAO brand-name. The transition of a government-funded institution like AAO is a complex and often emotional process. In AAO's case, it involves a revision of the Act of Parliament that brought the Australian Astronomical Observatory into being in 2010, as well as all the complex transition procedures for staff and assets. And the bottom line is that the university consortia that will now operate the two residual components of AAO must do so with funding that is significantly less than before. While every effort is being made to minimize the losses of staff in the transition, there are clearly significant risks to jobs and wellbeing. Uncertainty is the principal enemy of a smooth transfer, and a hard-working AAO Transition Team has been liaising throughout with stakeholders, including staff, the Science and Commercialisation Policy and the Corporate Divisions of DIIS and the principal universities. How successful this has been will not truly be known until the dust settles, but there are encouraging signs that things will return to “business as usual” soon after the transition. Indeed, with the instrumentation group becoming part of a truly national capability, business as usual could soon be bigger and better than ever. An AAO retrospective The history of the AAO, from its inception to its incorporation as an all-Australian institution in 2010, has already been covered in these pages (Watson & Colless 2010). Serious fans of the AAO are also encouraged to seek out the details of its origins in Gascoigne et al. (1990), and the highly personal account by Hoyle (1982). From the moment HRH Prince Charles arrived to “declare this aperture open” on 16 October 1974, the AAT's early history was unashamedly triumphal, with the pioneering colour imagery of David Malin taking the telescope firmly into the popular media, and early electronic detectors like the Image Photon Counting System reaping an enviable harvest of scientific discovery. Perhaps it is not too immodest to suggest that the observatory's final eight years have been equally successful, despite its observational facilities slipping inexorably down the world's ranking of large telescopes. As we shall see, however, size isn't everything. Hot on the heels of the 2010 transition came the proceedings of an unusual conference that mixed nostalgia with history and hard science (Cannon & Malin 2011). The volume is littered with astronomical household names, including the Anglo-Australian Observatory's five directors (Joe Wampler 1974–76, Don Morton 1976–86, Russell Cannon 1986–96, Brian Boyle 1996–2003 and Matthew Colless 2004–12). It was perhaps fitting that Colless, as AAO's first Australian-born director, should steer the observatory through the transition to all-Australian status. He resigned in 2012 to take up his present position as director of ANU's Research School of Astronomy and Astrophysics – which, of course, operates Siding Spring Observatory. It was during the interim directorship of Andrew Hopkins, early in 2013, that Siding Spring faced its most serious challenge. The Wambelong bushfire began in the heart of the adjacent Warrumbungle National Park and, fanned by hot January winds, quickly enveloped the mountaintop before bearing down on the nearby town of Coonabarabran. Before reaching Coona's outskirts, it abruptly changed direction, sparing the town but remaining dangerous for another week (figure 5). In the event, 55 000 hectares of national park and bushland were destroyed, along with more than 50 homes, fortunately without loss of life or serious injury. All the observatory's telescopes survived, albeit with some smoke and ash damage, but the astronomers' lodge was burned to the ground. It was in June 2017 that the ANU formally opened a new purpose-built lodge – but not before the building had been thoroughly tested by a large production team from the Stargazing Live TV programme. The AAT and some of its staff featured prominently in episodes broadcast by both the BBC and the Australian Broadcasting Corporation, continuing a long tradition of effective science outreach at the AAO (figure 6). 5 View largeDownload slide Siding Spring's worst day. With 50 m flames leaping up the southern flank of the mountain, the AAT and UKST (right) disappear into the smoke on 13 January 2013. All the telescopes survived. (R Paterson) 5 View largeDownload slide Siding Spring's worst day. With 50 m flames leaping up the southern flank of the mountain, the AAT and UKST (right) disappear into the smoke on 13 January 2013. All the telescopes survived. (R Paterson) 6 View largeDownload slide Famous faces under the Anglo-Australian Telescope. Brian Cox and Dara Ó Briain host BBC TV's Stargazing Live in March 2017. The ABC will repeat the show this year. (Á López-Sánchez) 6 View largeDownload slide Famous faces under the Anglo-Australian Telescope. Brian Cox and Dara Ó Briain host BBC TV's Stargazing Live in March 2017. The ABC will repeat the show this year. (Á López-Sánchez) A further consequence of the Wambelong fire was the early introduction of remote observing on the AAT, prompted by lengthy restrictions in accessing the site. This began in an improvised observing suite at North Ryde and is now the preferred method of observing for about half of the AAT's users, with dedicated observing facilities available at several other Australian institutions as well as North Ryde. It is expected that within the next year, the UKST will also be operable remotely. By the end of 2013, AAO's penultimate director was in post. Warrick Couch had been a chair of the AAT Board and, as director, negotiated the organization through the maze of regulation associated with its status as a division of a government department. Following Couch's resignation for personal reasons in December 2017, Jane Urquhart of DIIS took over AAO's helm for its final six months. Instruments and surveys From the beginning, the AAO's Sydney-based scientists and engineers showed themselves to be adept at building novel instruments for use with the AAT. It was the early use of optical fibres, however, that set the observatory on its current course. While multi-fibre spectroscopy was not invented by the AAO, it was transformed from an interesting novelty into a highly productive technique at both the AAT and the UKST during the early 1980s. Pilot spectroscopic surveys on both telescopes demonstrated its potential and, in the mid-1990s, the AAO unveiled 2dF (for 2-degree Field) on the AAT. This ground-breaking instrument allowed the spectra of 400 objects to be obtained simultaneously using fibres positioned robotically in a field of view that was unprecedented on a 4 m class telescope. 2dF's first task was a three-dimensional survey of the distribution of galaxies within some 750 Mpc to provide a detailed cross-section of the universe. That project – the 2dF Galaxy Redshift Survey – measured 221 000 galaxies and was completed in 2002, quickly becoming one of the richest sources of AAO scientific papers to date. In 2005, it was used to find the “missing link” between the temperature fluctuations in the cosmic microwave background radiation and today's distribution of galaxies. Building on this achievement, the AAO constructed a succession of room-sized spectrographs to be fed remotely by 2dF. In 2006, the intermediate-dispersion AAOmega became the telescope's workhorse for both galactic and extragalactic astronomy, and is still one of the world's most powerful spectroscopic survey instruments. It was followed in 2014 by HERMES, a high-dispersion spectrograph that was especially designed for galactic archaeology using detailed observations of very large numbers of individual stars. The current Galactic Archaeology with HERMES (GALAH) project has already netted the spectra of half a million stars. Another recent innovative instrument is the Sydney-AAO Multi-Object Integral field spectrograph, SAMI, which deploys 13 integral field units (IFUs) over a 1° field of view and is being used to conduct the first major IFU survey of nearby galaxies. Other AAT instruments currently in development include HECTOR (a considerably more powerful version of SAMI) and Veloce, a stabilized high-resolution (R ∼ 80 000) echelle spectrograph with precision wavelength calibration for stellar spectroscopy. The 6dF on the UKST Not to be outdone by its larger sibling, the UKST (figure 7) began a new role as a dedicated spectroscopic survey telescope in 2001 using a robotic instrument called 6dF, built as a prototype for the OzPoz fibre positioner (figure 8) delivered to UT2 of the VLT in 2003. Its first major project was the 6dF Galaxy Survey (6dFGS), measuring the redshifts of 150 000 galaxies, and peculiar motions for a substantial subset. The 6dFGS was finished in 2005 and the telescope went on to carry out the RAVE survey (for RAdial Velocity Experiment), a multinational project to measure the radial velocities and physical parameters of half a million stars. RAVE was completed in 2013, and its scientific legacy is still being exploited. But another key aspect of RAVE was that it pioneered a new mode of operation for the UKST, in which funding was provided by external contributions and was thus cost-neutral for the AAO. Eventually, perhaps, the AAT itself will be run on these lines for large-scale surveys. 7 View largeDownload slide The definitive portrait of the UKST in the 6dF era, with the robot room on the left and the spectrograph enclosure on the right. The screen is for calibration exposures, not midnight movies. (B Wrigley) 7 View largeDownload slide The definitive portrait of the UKST in the 6dF era, with the robot room on the left and the spectrograph enclosure on the right. The screen is for calibration exposures, not midnight movies. (B Wrigley) 8 View largeDownload slide AAO gets its own back. The OzPoz fibre positioner was built by the AAO for the VLT's FLAMES multi-object spectrograph. This early example of Australian equipment on overseas facilities is likely to be repeated under the new strategic partnership. (ESO) 8 View largeDownload slide AAO gets its own back. The OzPoz fibre positioner was built by the AAO for the VLT's FLAMES multi-object spectrograph. This early example of Australian equipment on overseas facilities is likely to be repeated under the new strategic partnership. (ESO) This funding model is now being used in two new UKST surveys. They are Taipan (two million galaxies with r < 17.5 for cosmological and extragalactic studies, complementing a major project on ASKAP – the Australian Square Kilometre Array Pathfinder) and FunnelWeb (three million stars to generate the “Henry Draper Catalogue of the 21st century”, with synergies relating to TESS and Gaia). Both are externally funded and use a novel fibre-positioner recently commissioned on the newly refurbished UKST (figure 9). Each fibre is now positioned by its own micro-robot, rather than with a pick-place machine like 2dF. All the fibres can be moved simultaneously, reducing reconfiguration time to a few minutes and avoiding the calibration overheads introduced by slit exchangers. This Starbugs technology has been developed by AAO as a demonstrator for MANIFEST, the proposed Many Instrument Fibre System on the 24.5 m Giant Magellan Telescope. In the present setup, 150 autonomous fibres patrol the 6° field of the UKST, but funding has been secured to increase that to 300 fibres. 9 View largeDownload slide Starbugs on the glass focal plate of the UKST. Each 8 mm diameter vacuum-adhered “bug” contains an autonomous positioning robot, three metrology fibres (illuminated) and a science-fibre payload. (A Green) 9 View largeDownload slide Starbugs on the glass focal plate of the UKST. Each 8 mm diameter vacuum-adhered “bug” contains an autonomous positioning robot, three metrology fibres (illuminated) and a science-fibre payload. (A Green) Data Central Not quite an instrumentation project, but vitally important for archiving and disseminating survey data, is AAO's Data Central. This new project, designed specifically to meet the needs of the Australian astronomical community, was funded by DIIS to provide a large-scale data archive capable of being scalable and extensible, as well as able to ingest and cross-match heterogeneous data. Launched in August 2017 with three sample datasets, Data Central is rapidly growing, and can be accessed at http://datacentral.aao.gov.au. Other current AAO instrument projects include AESOP, a 2400-fibre tilting-spine positioner for ESO's 4 m VISTA telescope, and the Gemini High-Resolution Optical SpecTrograph (GHOST), which has been developed for the Gemini South telescope in a collaboration between AAO, the Herzberg Institute for Astrophysics in Canada, and the ANU. More fundamental instrumentation research is also carried out, particularly in astrophotonics. In collaboration with scientists at the University of Sydney, Macquarie University and the University of Western Australia, AAO has tested OH-suppression devices based on fibre Bragg gratings, and experimented with waveguide photonic spectrographs, ring resonators and photonic-comb calibration cells. These devices, or their successors, are expected to radically change the way in which astronomical instruments are built, and add wholly new capabilities. Plus ça change… One of the key ingredients for the success of the AAO over the years has been the relationship between the two ends of the organization. Yes, there has always been banter between them (typically “Coona has broken it again” vs “As usual, Epping has sent us a half-finished job”), but their mutual reliance and trust has delivered many a fine instrument at the cutting edge of astronomical technology. From 1 July, the telescope staff and the instrument builders will belong to separate organizations, and the connection between them will not be automatic. However, all parties are well aware of this requirement, and steps are being taken to preserve it. Less likely to survive is the AAO's student fellowship programme. For many years now, the AAO has invited astronomy undergraduates to apply for 12-week placements during the long vacation. Because AAO was originally a bi-national institution that straddled the equator, that meant two student intakes for the northern and southern summer vacations, a tradition that continued in the all-Australian era. Competition for places was intense, but students always benefited from the experience, with many going on to become professional astronomers or instrument scientists. In fact, one former student became director of AAO itself. The programme continued the tradition of mentorship established in the early years of the AAO, when it was known as a “finishing school” for young astronomers. Because both halves of the former AAO will now be housed in universities, it seems probable that the December 2017 intake of AAO students will be the last in the current series. However, for the same reason, there will be many new opportunities for student vacation scholarships and full-scale student projects at both undergraduate and graduate level. Beside its staff, its instrumentation programme and the efficiency with which its telescopes are operated, there has been one other major ingredient to AAO's success: its environment. Yes, Siding Spring's record of clear weather is not brilliant (typically 67%) and neither, by today's standards, is its level of atmospheric turbulence (median seeing 1.5 arcsec). But what it can offer is a night sky as dark today as it was when its first inhabitants looked skywards tens of thousands of years ago. Today, remoteness is no guarantee of dark skies, and the light-plumes of cities can certainly be detected low on Siding Spring's horizon. But in 1990, state legislation was enacted in New South Wales to protect the observatory's skies by regulating lighting installations out to 100 km from Siding Spring. Almost a decade later, the observatory's Dark Sky Committee was formed to update the regulations in the light of technological and legislative changes, a process that came to fruition in 2016 with the introduction of a comprehensive new lighting code. In parallel with this work, the Dark Sky Committee spearheaded a proposal to have the adjacent Warrumbungle National Park recognized as Australia's first Dark Sky Park. This culminated in the award of Gold Tier Status by the International Dark Sky Association, also in 2016. As well as promoting tourism in the area, the Dark Sky Park will also help maintain the pristine skies of the observatory. Epilogue It is now more than a decade since the AAT was feted as the first-ranked 4 m telescope in the world. The ranking covered both productivity (number of papers) and impact (number of citations), with 2.3 times as many citations as its nearest competitor (Trimble & Ceja 2007). Moreover, at the time, the AAT was ranked just fifth in productivity and impact among optical telescopes of any size, on the ground or in space. What is remarkable about those figures is that they were achieved not when the telescope was in its first flush of youth, but relatively late in its life. They demonstrated the efficacy of the large-scale survey strategies set in place in the mid-1990s, when 2dF was being commissioned. While the international landscape today is somewhat different, with a number of telescopes poised to carry out similar work, those performance figures hold out the promise that the AAT will remain productive for a much longer period than is currently guaranteed. With the continuing commitment and loyalty of astronomers past and present to the AAO, that promise is bound to be fulfilled. ACKNOWLEDGMENTS A great many people have contributed to the work reported in this article. A number of key individuals in the Australian government, DIIS, AAL and the universities have put in an enormous amount of effort in brokering the partnership with ESO and the AAO transition. Also noteworthy is the work of the AAO Transition Team and the DIIS Optical Astronomy Group. We thank Emmi Mikedakis, Matthew Colless and Mike Steel for helpful comments on the article, and Warrick Couch and Neville Legg for earlier discussions. Perhaps the biggest thank you should go to the staff of the AAO, for their extraordinary achievements in the day-to-day running of the facility, and their forbearance in what is unquestionably a difficult period. REFERENCES Australian Academy of Science 2015 Australia in the Era of Global Astronomy: the Decadal Plan for Australian Astronomy 2016–2025 (Canberra) Cannon R & Malin D (eds) 2011 Celebrating the AAO Past, Present and Future (Australian Government) Gascoigne S C B et al. 1990 The Creation of the Anglo-Australian Observatory ( Cambridge ) Hoyle F 1982 The Anglo-Australian Telescope ( University College Cardiff Press ) Trimble V & Ceja C A 2007 Productivity and impact of astronomical facilities: a statistical study of publications and citations AN 328 983 Watson F & Colless M 2010 Astron. & Geophys. 51 3.16 © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty100

CAREERS One of the first initiatives to come out of the new funding body UK Research and Innovation aims to attract and sustain outstanding researchers with the potential to lead in t he future. UKRI has made the Future Leaders Fellowships open to applications from across the UK research landscape, including those working in business. The scheme offers long-term funding over seven years, with a four+three-year model and a review in year four. Part of the aim is to make it easier for people to move between sectors, between business and academia for example, to develop new research and innovation career paths. There will be six calls for applications between now and 2020/21, and UKRI expects to award around 100 fellowships in each, across all UK research. The first round, for which applications close on 3 July this year, will be smaller, around 50 awards. Full details are on the UKRI website. http://bit.ly/2JLkVCe © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty127

STAR FORMATION The first large-scale age map of stars in the Milky Way has shown that stars in the galactic bulge formed 11–7 billion years ago. Marina Rejkuba (European Southern Observatory) and team used data from the VISTA Variables in the Via Lactea (VVV) infrared survey. They compared simulations with VVV data and spectra of 6000 stars from the GIRAFFE/FLAMES instrument on ESO's Very Large Telescope. “Our findings were not consistent with a purely old Milky Way bulge,” said Rejkuba, “but require star formation lasting around 4 billion years and starting around 11 billion years ago. The youngest stars are at least 7 billion years old, which is older than some previous studies had suggested.” Their data do not allow discrimination between stars in the bar and the bulge, but indicate that the bar had formed by 7 billion years ago. http://bit.ly/2KqOQAR © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty121

We are grateful for these recent donations to the RAS Library: View largeDownload slide View largeDownload slide • Schrijver C J, Bagenal F & Sojka J J (eds) 2016 Heliophysics: Active Stars, their Atmospheres, and Impacts on Planetary Environments (Cambridge University Press, Cambridge). View largeDownload slide View largeDownload slide • Gribbin J & Gribbin M 2017 Out of the Shadow of a Giant: Hooke, Halley & the Birth of British Science (William Collins, London). View largeDownload slide View largeDownload slide • Catling D C & Kasting J F 2017 Atmospheric Evolution on Inhabited and Lifeless Worlds (Cambridge University Press, Cambridge). View largeDownload slide View largeDownload slide • Schilling G 2017 Ripples in Spacetime: Einstein, Gravitational Waves, and the Future of Astronomy (Belknap Press, London). View largeDownload slide View largeDownload slide • Genta G 2017 Next Stop Mars: the Why, How, and When of Human Missions (Springer, Switzerland). http://www.ras.org.uk/library © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty109

DIVERSITY The RAS has created a website about the position of women in the Society, in the past and present. Blogs and regular tweets featuring women – well-known and obscure – highlight aspects of women's contributions to our sciences. http://women.ras.ac.uk © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty107

View largeDownload slide View largeDownload slide DATA RELEASE The eagerly anticipated second release of data from ESA's Gaia star mapper on 25 April 2018 did not disappoint: DR2 has positions and magnitudes for 1.7 billion stars and half-a-million quasars, and parallaxes, proper motions and blue/red photometer colours for 1.3 billion of those stars. As an addition to the Gaia data for this release, there are also radial velocities for 7 million stars; light curves and classifications for half-a-million variable stars; positions of 14 000 asteroids and key astrophysical parameters (stellar effective temperature, extinction, reddening, and radius and luminosity) for tens of millions of stars. It has also established a new version of the celestial reference frame, the first optical reference frame based exclusively on extragalactic sources. The image shows a cropped, rotated view of the brightnesses of the 1.7 billion sources in Gaia DR2. (ESA/Gaia/DPAC, A Moitinho/A F Silva/M Barros /C Barata, Univ. Lisbon, Portugal; H Savietto, Fork Research, Portugal) http://sci.esa.int/gaia © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty120

MILKY WAY Our galaxy could contain several wandering supermassive black holes, as well as the central one, as a result of galaxy mergers, according to a study published in The Astrophysical Journal. Modelling by Michael Tremmel (Yale University, USA) and colleagues suggests that there would be several such wanderers in a galaxy the size of our own. They are hard to find, the team says, because there is little gas for them to accrete, outside the central bulge of galaxies. http://bit.ly/2jkpnwG © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty136

AI One day, humans will send spacecraft to exoplanets. Those autonomous spacecraft will need to decide which planets to focus on and researchers from the Centre for Robotics and Neural Systems at Plymouth University have made a start on the systems that will be needed. Christopher Bishop described an artificial neural network that they have trained to classify planets, based on five rocky solar system bodies with atmospheres: Earth today, early Earth, Mars, Venus and Titan. The team has trained the system using more than 100 spectra and indicators of habitability. https://bit.ly/2HIFWAM © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty108

View largeDownload slide View largeDownload slide ONLINE Open University students gathered on 20–22 April to get together to revise, make friends and observe the skies. Read more online at A&G Forum. https://aandg.org/sections/people/ou-astro-weekend © 2018 Royal Astronomical Society

Bowler, Sue

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty150

Sue Bowler ponders ideas on how and when plate tectonics began and what it means for Earth and other planets. Earth is the only rocky body in the solar system with plate tectonics. This system of lithosphere plates in constant motion forms a link between the deep Earth and the atmosphere; it may be important for the origin and survival of life on Earth. If so, the existence of plate tectonics on an exoplanet may indicate habitability. But why does Earth have plate tectonics? When and how did it start? Is it an inevitable stage in the cooling of rocky planets? Does it require some catastrophic event to get started? The Royal Society discussion meeting “Earth dynamics and the development of plate tectonics” took place in London on 19 and 20 March 2018 and tackled these questions and more in a wide-ranging series of presentations and discussion. There were perspectives from planetary science, geochemistry and geodynamic modelling brought to bear on the evolution of the early Earth – and a realization from several speakers that a clear definition is the place to start the discussion (see box “Defining plate tectonics”). In this overview, I explore geophysical aspects of the place of plate tectonics in the evolution of planet Earth. Looking back in time Plate tectonics processes – rifting, collision, subduction – shape the Earth today, but in doing so they remove evidence of how the planet has evolved. “Earth is a dynamic planet,” noted Tony Kemp (University of Western Australia), “smudging and erasing the early record.” With this limited rock record, this meeting took an oblique approach, considering three approaches to the evolution of plate tectonics: geochemical analysis, geodynamic modelling and comparative planetology. Geochemical analysis is a powerful tool that unpicks how elements and isotopes are partitioned as a result of geological processes such as melting and crystallization. When radioisotopes are partitioned, the proportions of preserved decay products allow dating of the events. But without much of a rock record for the first half billion years, exploring the origins of the Earth means looking off the planet. The oldest rocks dated in the solar system are meteorites, with radiometric ages of up to 4.6 Ga. These dates record the solidification of the first planetary bodies in the solar system, the class of objects that went on to accrete and form Earth. “The planetesimals formed very rapidly, in less than 3 million years,” said Laura Schaefer (Arizona State University, USA). “They grew while gas was still present in the disc … and probably had high volatile content.” Earth grew by accretion – and the collisions together with higher levels of radioisotopes led to heating and melting. The few rare rocks dated at older than 4000 Ma record the formation or reworking of the early crust, but lack context. These pinpoint techniques have the potential to offer invaluable “ground truth” for models of planetary evolution. This overview will focus on what can be learnt from planetary modelling and comparisions with other silicate bodies in the solar system. As a starting point, Bob Stern (University of Texas at Dallas, USA) noted that the other silicate bodies in the solar system give glimpses of how Earth might have been before plate tectonics: they all show some sort of single lid or stagnant lid structure. This is the starting point for geodynamic models of mantle circulation and lithosphere growth, i.e. a continuous outer layer that forms as the planet cools. The lithosphere thickens and strengthens with age, and models can replicate the slightly denser lithosphere above a lower density asthenosphere that is characteristic of Earth's ocean plates today. The development of thick lithosphere is hampered by the high heat flow; when the outer layer reaches around 20 km thick, the base tends to melt and drip back into the mantle below – what Stern and others called “drip tectonics”. Drip tectonics would not work in the same way as plate tectonics, although it would return surface rock to the deeper Earth below. As the model lithosphere strengthens, the problem of weakening it to form plate boundaries increases. Drip tectonics would also make any subduction difficult to sustain; the higher mantle temperatures would melt the descending slab, losing the link with the surface lithosphere. And soft, drippy descending slabs bring problems for developing coupled rifting and a global plate system. Adrien Lenardic (Rice University, Texas, USA) discussed mantle flow and the link between the high-viscosity lithosphere and the low-viscosity asthenosphere below and what part changes in mantle viscosity play over Earth history. His geodynamical modelling led him to suggest that there may be two problems to solve in the dynamics of plate tectonics: how it began and how it is maintained. Brad Foley (Penn State University, USA) combined early Earth models with damage theory to examine the development of weak plate boundaries on a hot young Earth. He stressed the importance of considering means other than plate tectonics to move the lithosphere horizontally and into the mantle (Foley et al. 2012). “The transition between mobile lid and stagnant lid is the major geodynamical transition,” said Foley, “and mobile encompasses a broad range of behaviours including plate tectonics, episodic subduction, sluggish lid and so on.” 1 View largeDownload slide Simone Marchi's conception of an early Earth, with a surface pockmarked by impacts, resulting in extrusion of deep-seated magma, while other, distant, parts of the surface could have retained liquid water. (SwRI/Simone Marchi) 1 View largeDownload slide Simone Marchi's conception of an early Earth, with a surface pockmarked by impacts, resulting in extrusion of deep-seated magma, while other, distant, parts of the surface could have retained liquid water. (SwRI/Simone Marchi) Craig O'Neill (Macquarie University, Australia) focused on modelling how plate tectonics began. He argued that it would take some forcing of a single lid planet – from mantle plumes, volcanic loading or impacts – in order to start subduction. “Geodynamic models suggest that the Earth system was sensitive at about 3 Ga possibly with marginal stability,” O'Neill said. “External forcing could tip the balance, by mantle plumes, volcanic loading or meteorite impacts.” He suggested that stop-start subduction, possibly initiated by these processes, was a precursor to a mobile surface and the establishment of plate tectonics. The idea that a catastrophic event might disrupt the young lithosphere enough to trigger subduction has been explored using the examples of other rocky bodies in the solar system, notably Venus. Defining plate tectonics Any discussion of the role of plate tectonics in Earth dynamics and history has to start with a definition of plate tectonics itself, and go on to establish how it might be recognized in the rock record. Speakers at the meeting gave a variety of definitions that included four elements: strong rigid lithosphere plates; weak persistent plate margins; horizontal movement relative to other plates; and circulation between the surface and deep Earth. All agreed that the term “plate tectonics” refers to the global system of coupled ridges, trenches and transform faults that defines the surface of the Earth today. One element of the system is not enough to deduce that the planet-wide cycles are operating. Strong lithosphere. Development of strong rigid lithosphere matters for plate tectonics because Earth today has plates thousands of kilometres wide, able to transmit stress from one side to the other. The cold ocean lithosphere is ∼1% denser than the mantle immediately beneath; this gravitational instability means that subduction continues once a plate slides into the mantle below at a plate margin. Plate boundaries. While today's plates are strong, the margins where the relative movement takes place are weak. Oceanic plate boundaries are up to thousands of kilometres long but only tens of kilometres wide, defined by the earthquakes that indicate fault motion in the upper parts of the plates. Continental plate boundaries are wider, but are also defined by fault zones. The problem for the inception of plate tectonics is how to develop such long-lived linear weak zones. Relative movement. The horizontal motion of the plates, at speeds around a few centimetres per year, is another characteristic of plate tectonics. But the driving mechanism remains unclear; there is no simple link with mantle convection. The ability of the lithosphere to transmit stress plays a part in plate movements. At subduction zones, the descending cold slab exerts a downward force – slab pull – on the rest of the plate. The effects of lithosphere cooling, solidification and thickening at the mid-ocean ridge also act to move the young plate away from the ridge. These forces in combination may be enough to sustain subduction once it has started. Chemical cycles. The subduction of lithosphere in plate tectonics plays an important role in cycles that move elements important for life between the deep Earth, surface, oceans and atmosphere. Weathering of silicate rocks by rainwater acidified in the atmosphere brings carbon and oxygen into the oceans and ocean sediments; subduction takes those volatile components into the mantle, where some of them are returned to the atmosphere in volcanic eruptions. This cycle acts as a negative feedback on global temperature change, acting faster when the temperature is higher, for example. Similar cycles between atmosphere and deep Earth operate for other volatile elements and may be important in maintaining nutrients for life through geological time. Twin planet While it is received wisdom that Venus underwent a global resurfacing event in the geologically recent past, re-evaluations of the data from Magellan and Venus Express suggest that such a catastrophic recent event is not necessary. Sue Smrekar (Jet Propulsion Laboratory and Caltech, USA) described features on Venus that look like continents and plate boundaries on Earth – although she stressed that Venus does not have evidence of plate tectonics. In the 1990s, with Magellan data, regions of Venus were identified as like the trenches found on Earth at subduction zones (e.g. McKenzie et al. 1992). While the identification of linked plate boundaries on Venus proved optimistic, Smrekar showed that there are features that could indicate subduction, possibly episodic, around a mantle plume. A large plume would create a bulge in the lithosphere; weak zones could develop around the margin where the stretched and elevated lithosphere overrode the surrounding surface. Vicky Hansen (University of Minnesota at Duluth, USA) described the large-scale remapping of part of Venus, over an area from 60°–180°East, stretching across 10 000 km (Bannister & Hansen 2010, Hansen & Olive 2010). Artemis Corona, a 2400 km diameter roughly circular topographic high, is bounded by Artemis Chasma, a narrow circular trough 1–2 km deep and 25–100 km wide. Hansen described more extensive systems of fracturing consistent with plume upwelling. The circular mantle plume structures are superimposed on older terrain interpreted as forming as a “skin” on magma oceans resulting from large early impacts on the thin ancient lithosphere of Venus. Hansen compares these impact-related structures to features of the Earth: Archaean granite–greenstone belts, formed from 2.5–4 Ga (Hansen 2015). “We have the conditions for subduction,” said Smrekar. “The crust and lithosphere were gravitationally unstable and would sink if the lithosphere were to break.” On Venus, plumes could be part of the resurfacing mechanism and subduction induced in this way would return volatiles to the mantle, possibly helping to form crust comparable to continental crust on Earth. “It's important for Earth and for exoplanets,” said Smrekar. “The early Earth had a hotter mantle and thinner lithosphere. Plume subduction could become plate tectonics as the planet cooled.” Taken together, the evidence suggests that subduction might have started on Venus in response to a super plume or a major bolide impact. How it might evolve is another problem; as Hansen pointed out “it's not plate tectonics until it's global”. Venus appears to be a useful analogue for the early Earth, but there are limits to its usefulness because Earth went on to develop plate tectonics and Venus didn't. Looking back at Earth Thinking of Earth as a single-plate planet that changed to a mobile multiplate system raises the question of when this might have happened, how often, and if evidence of the change might be present in the geological record. Several speakers addressed the challenges of extracting useful data from the sparse geological record before 3500 Ma. Kemp addressed the problems of Earth's geological archives. “The rock record is sparse. Less than one-millionth of the exposed crust is older than 3500 Ma. Is there a preservation bias? Is this representative?” In addition, he noted that the few truly ancient rocks such as the Acasta gneiss are complex and sample selection can introduce further bias. Kemp suggested that the rock record is usable – but with care. Peter Cawood (Monash University, Australia) proposed that evidence for the existence of plate tectonics could include evidence of rigid lithosphere – such as dyke formation – and metamorphic rock associations as found around subduction zones today. His overview indicated significant changes in geological processes at around 3 Ga, suggesting that this was when plate tectonics became established, as the mantle cooled and the lithosphere strengthened. There is other evidence of major changes around 3 billion years ago. Bruno Dhuime (CNRS and the University of Montpellier, France) used the geochemistry of the crust to track continental growth, which faltered at around 3 Ga (Dhuime et al. 2015) and ascribed it to the onset of plate tectonics, noting other changes in the nature of the crust at this time. The geodynamic approach points the same way: “Around 3 Ga, something changed,” said O'Neill, “the record shows systematic differences from what had gone before.” Jun Korenaga (Yale University, USA) used the slow-down in continental growth at around 3 Ga to consider the role of water in mantle circulation and the growth of the continents (Korenaga 2018). Taras Gerya (Swiss Federal Institute of Technology, Zurich) examined models of crustal growth associated with mantle plumes. He linked plume processes to the growth of crust on Earth at more than 3.5 Ga, covering a variety of routes to forming the thick rigid lithosphere needed for plate tectonics. Equally, the onset of plate tectonics in the modern sense could be more recent, in the Neoproterozoic eon (from 1000–500 Ma), when life became multicellular and the Earth underwent several extreme episodes of glaciation known as Snowball Earth. Stern listed many geological features found in the past 500 million years and rarely or never before, suggesting that the Neoproterozoic upheavals marked the transition from a single lid regime to plate tectonics. He argued for a long period of proto-plate tectonics before the establishment of the modern dynamics in the past billion years or so (Stern & Miller 2018). Cin-Ty Lee (Rice University, Texas, USA) argued that continents need thick crust and that a combination of magmatism and horizontal compression – possibly by plate movements – are required to make it. He suggested that lithosphere thickening would result in the emergence of stable continents at around 700 Ma. When the lithosphere was generally thinner, the continents would be underwater except for active orogenic belts. Early Earth could look very different – a water world – despite the same tectonic processes operating for much of its history. This change could even play a part in the Cambrian explosion, when multicellular lifeforms first proliferated (Lee et al. 2017). Tim Lyons (Alternative Earths Astrobiology Center at the University of California at Riverside, USA) reviewed milestones in the history of life, based on an improved curve of oxygen levels on Earth through time (Lyons et al. 2014). He ascribed the flowering of life after 800 Ma to increased oxygen levels, associated with intense and continuous crustal uplift. Aubrey Zerkle (University of St Andrews, UK) described the nitrogen cycle, similar to the carbon cycle in that the deep Earth is by far the largest reservoir and plate tectonics provides a return route to the mantle as part of a global cycle. For life to thrive without plate tectonics, there may have been a different process to cycle nitrogen and other elements necessary for life, such as phosphorus, into the mantle and back to the atmosphere (Zerkle & Mikhail 2017). The early Earth, with fossil life known from 3500 Ma, must have had some mechanism for supplying the necessary elements. Plate tectonics drives this cycle on Earth today, but it is not the only way to do so. Open questions Although the presentations and discussion at the meeting led to a broad consensus that the Earth began as a single-plate planet and went on to develop plate tectonics, the process, its timing and effects on the Earth system remain mysterious. The most fruitful ways forward seem likely to involve a combination of approaches. Above all, we have to determine what data indicates that plate tectonics was operating. The exquisite precision offered by geochemical analysis demands context from planetary models. Geodynamic models need better data on rock properties – and they need to move from two-dimensional slices of the planet to computationally challenging three-dimensional, global simulations. There are many ideas about the Earth before plate tectonics and it is possible that plate tectonics started many times; we need to find ways to test models of early Earth dynamics. And a new mission to Venus would be immensely valuable in exploring this early-Earth analogue. A better understanding of Earth's planetary dynamics will, in turn, feed into the exploration of exoplanets. While no-one is going to be seeing plate boundaries on exoplanets in the foreseeable future, we are finding ever more planetary systems, like and unlike our own. A clearer understanding of how and why this dynamic regime became the norm for Earth, but not for other planets and moons in the solar system, will support the search for extraterrestrial life. Perhaps it is a coincidence that the only planet with life also has plate tectonics – but it may not be. MORE INFORMATION This overview was inspired by the presentations and discussion at the Royal Society discussion deeting on “Earth dynamics and the development of plate tectonics”, organized by Prof. Chris Hawkesworth FRS, Prof. Michael Brown, Prof. Mary Fowler and Dr Jeroen van Hunen and held on 19 and 20 March 2018. The meeting covered a wider range of topics than discussed here and the interpretations are my own. Recordings of the presentations will be available at http://royalsociety.org/science-events-and-lectures/2018/03/earth-dynamics-tectonics and the papers will be published in Philosophical Transactions A. REFERENCES Bannister R A & Hansen V L 2010 US Geological Survey Scientific Investigations Map 3099 scale 1:5 000 000 http://pubs.usgs.gov/sim/3099 Dhuime B et al. 2015 Nature Geoscience 8 552 CrossRef Search ADS Foley B J et al. 2012 Earth Planet. Sci. Lett. 331–332 281 CrossRef Search ADS Hansen V L & Olive A 2010 Geology 38 467 CrossRef Search ADS Hansen V L 2015 Lithosphere 7 563 CrossRef Search ADS Korenaga Y 2018 Earth Planet. Sci. Letters 482 388 CrossRef Search ADS Lee C T A et al. 2017 Int. Geology Review 60 : 4 431 CrossRef Search ADS Lyons T W et al. 2014 Nature 506 307 CrossRef Search ADS PubMed McKenzie D et al. 1992 J. Geophys. Res. 97 13533 CrossRef Search ADS Stern R J & Miller J R 2018 Terra Nova 30 87 CrossRef Search ADS Zerkle A L & Mikhail S 2017 Geobiology 15 343 CrossRef Search ADS PubMed © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty125

OUTREACH One of the Society's new bicentenary outreach projects got off to a flying start over Easter, getting Truro residents and tourists alike talking about astronomy. Cornwall Sea to Stars aims to share astronomy and space science with the people of Cornwall. It held its launch event over the Easter holiday weekend at the Lemon Quay in Truro, highlighting the fishing and navigation heritage of the region. But the focus of the events was very much on today's science. On a breezy but bright Good Friday, alongside the craft market, were solar telescopes, binoculars, displays of astronomical images and meteorites and a host of volunteers in bright blue jumpsuits with the Sea to Stars mission patch. Children were the focus of the two-day launch event, with an astronomy-themed treasure hunt – and their parents liked the group's plans. “The thing I'm being asked most,” said Clint O'Connor, chair of the project, “is when can you come to our school?” Read more online at A&G Forum. View largeDownload slide Outreach in action in Truro. (M Wrigley) View largeDownload slide Outreach in action in Truro. (M Wrigley) http://cornwallseatostars.org.uk https://aandg.org/blog/sea-to-stars-launches-in-cornwall © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty112

HUBBLE The Hubble Space Telescope has imaged – for the first time – a star that survived the supernova explosion of its binary companion. Supernova 2001ig, in NGC 7424, showed signs of a surviving companion star in Gemini South data from 2004. The explosion was a Type IIb stripped-envelope supernova, in which most of the star's hydrogen was lost beforehand. In binary systems, the companion could draw off the hydrogen envelope. The HST image of the surviving companion star to 2001ig indicates that this is the case. http://bit.ly/2KfMjcF © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty129

GRAVITATIONAL LENSING Dark matter is not interacting with itself in the Abell 3827 cluster, after all. New data on this unusual galaxy cluster reported by Richard Massey (University of Durham) and colleagues suggest that the pattern of gravitational lensing is in accord with the standard cold dark matter model of the universe. In 2015, the same group found signs that one of the four galaxies at the heart of the cluster had an odd distribution of mass, offset from the visible part of the galaxy. This could be ascribed to self-interactions between dark matter that held it back from normal matter as the galaxies came together. Now the same team has added Atacama Large Millimetre/submillimetre Array data to their armoury, together with more spectroscopy from the VLT MUSE instrument. The infrared signal proved crucial to the improved model, which shows the mass distribution aligned with the stars for all four galaxies. The results are published by Massey et al. in Monthly Notices of the RAS. http://doi.org/10.1093/mnras/sty630 © 2018 Royal Astronomical Society

Spencer, Ralph;Rapley, Chris

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty149

Ralph Spencer and Chris Rapley explore the role played by Jodrell Bank in early attempts to detect cosmic rays – and how the technique is now becoming more widely used. The question of the origin of cosmic rays has dominated efforts in astroparticle research ever since their discovery by Victor Hess in 1911. Although likely sources at low energies are partly understood, the origin of the highest energy cosmic rays has remained a mystery. The basic problem is that high-energy events are rare, with cosmic rays of more than 1020 eV expected at a rate of 1 per km2 of the Earth's surface per century. Thus a detector covering a large area – hundreds of km2 – is needed in order to study reasonable numbers of events. High-energy interactions in the Earth's atmosphere produce many secondary particles in an extensive air shower before reaching the Earth's surface. Even so, plenty of particle detectors are required because the characteristic width of the shower is only ∼80 m for the electromagnetic cascade and ∼320 m for the muon component (Patrignani et al. 2006). These facts led Blackett and Lovell (1941) to suggest that it may be possible to detect distant showers by means of the radar echoes from the trail of ionization left behind the shower front as it passes though the atmosphere. Early experiments in 1946 took place in the Cheshire fields at Jodrell Bank, acquired by the University of Manchester as a botanical station. They used surplus military radars but failed to detect cosmic rays. Instead they found high-altitude trails of meteors and the work led to the rapid development of radio astronomy at Jodrell Bank (Lovell 1968). The reason for the non-detection was damping caused by the rapid capture of free electrons by neutral atoms and molecules in the lower atmosphere; hence the radar reflective trail from a passing cosmic ray has only a fleeting existence, lasting less than 100 ns. Various experiments have been proposed since (e.g. Gorham 2001), though none has proved successful at unequivocally detecting cosmic-ray air showers by radar. The passive radio story is, however, quite different. This technique has now become a useful addition to air shower studies, after a period of low activity from the early 1970s. Modern digital technology led to a revival in the 2000s (Falcke & Gorham 2003) and there has been a flurry of activity since, with major developments in understanding the emission mechanisms and the radio characteristics, together with new experimental techniques. It now seems appropriate to discuss some of the early work at Jodrell Bank before the remaining protagonists forget. The original idea The possibility that the secondary particle shower itself may emit at radio wavelengths was first suggested by John Jelley in his book on Cherenkov radiation (Jelley 1958). It was thought that the radio emission could possibly extend over a greater area than the particles over the ground, and that a large area could be covered relatively inexpensively. Early measurement at microwave frequencies proved unsuccessful. However, Askaryan (1962) suggested that the electromagnetic shower could contain an excess of electrons, caused by the in-flight annihilation of positrons. Because the electrons are relativistic, moving through the Earth's atmosphere where the velocity of light is less than c, and concentrated in a thin (∼2 m depth) shower front, then they could emit coherent Cherenkov radiation at wavelengths of a few metres. So perhaps observations at a few 10s of MHz would be successful after all. This idea led John Jelley to contact Neil Porter in Dublin and F Graham Smith at the Cavendish Laboratory in Cambridge (who was about to move to Jodrell Bank) with the suggestion of using a small array of Geiger counters to trigger radio detection of air showers, taking advantage of the relatively radio-quiet zone at Jodrell Bank. Some of this work has been reported in reviews by Weekes (2001) and Fegan (2012). The major review by Allan (1971) also described the results from a variety of experimental groups including those at Harwell, Dublin, Haverah Park (Leeds), Moscow, Karkov, Bologna, Penticton, Bolivia and Australia. The radio spectrum is rather crowded at wavelengths of a few metres. Because short pulses from the shower were expected, then a large bandwidth was needed. It was decided to use the frequency of 44 MHz, in the band used by the BBC TV video signal. Though this would mean operation during the daytime was not possible, the transmitters were turned off between the hours of 00:00 and 08:00 and so the nights were clear and free of interference. Electronic amplifiers covering the frequency band were also available from the Cavendish radio astronomy group. A suitable field big enough for a small particle detector array and antennas was found on the Jodrell Bank site, together with a hut to house the equipment and researchers. This is known as Blackett's Hut (figure 1) and had been built in 1948 free of magnetic materials to allow Patrick M S Blackett to investigate the production of a magnetic field from a rotating massive body, in this case 15.2 kg of gold that he had borrowed from a bank, in 1949 (Lovell 1975). 1 View largeDownload slide Blackett's Hut in the summer of 2008, now in a rather sorry state, though still containing evidence of the work done there in 1966 with a sketch of the particle detector array on the inside wall. In the 1960s, the hut contained the electronics and recording oscilloscope. 1 View largeDownload slide Blackett's Hut in the summer of 2008, now in a rather sorry state, though still containing evidence of the work done there in 1966 with a sketch of the particle detector array on the inside wall. In the 1960s, the hut contained the electronics and recording oscilloscope. The antenna was constructed in the summer of 1964 by Rob Porter, a graduate student at the University of Manchester. It comprised a 6λ by 6λ array of full-wave dipoles connected by open wire transmission line to a preamplifier and then by coaxial cable to the equipment in Blackett's Hut (Porter 1967). The particle detector array consisted of three trays of Geiger counters spaced 50 m apart in an equilateral triangle adjacent to the antenna, as shown in figure 2. 2 View largeDownload slide Layout of the equipment looking west, from a montage by R A Porter (1967). The dark area shows the position of the large array. The north–south corner reflector can be seen to the west of the array, in front of the Mk2 radio telescope. The white boxes contained the Geiger counters. 2 View largeDownload slide Layout of the equipment looking west, from a montage by R A Porter (1967). The dark area shows the position of the large array. The north–south corner reflector can be seen to the west of the array, in front of the Mk2 radio telescope. The white boxes contained the Geiger counters. Coincident pulses from the counters triggered an oscilloscope fitted with a recording camera. The radio signals from the antenna were delayed to allow for delays in the triggering system, filtered, amplified and the power measured before being displayed on the oscilloscope. Trevor Weekes, then a graduate student at the University College, Dublin, had built the Geiger array and came over to help with running the experiment, which formed part of his PhD thesis. Trevor was lucky enough to find a large radio event on the fifth frame of the film used on the first successful night of operation 20 August 1964, as he recounted amusingly in Weekes (2001). Operations continued until March 1965, producing 4500 triggered events with 11 clearly visible pulses in the expected delay window (figure 3). Results were published in Nature (Jelley et al. 1965) and in Nuevo Cimento (Jelley et al. 1966). 3 View largeDownload slide A radio event at 44 MHz as recorded during the first experiment in 1965. The sine wave was used as a timing check. The hodoscope – an array of light-emitting diodes – at bottom left showed which detectors were triggered. The clock and timing waveform were not used in later experiments. 3 View largeDownload slide A radio event at 44 MHz as recorded during the first experiment in 1965. The sine wave was used as a timing check. The hodoscope – an array of light-emitting diodes – at bottom left showed which detectors were triggered. The clock and timing waveform were not used in later experiments. Radiation mechanisms Further experiments at Jodrell Bank concentrated on determining the mechanism for the radiation. Jelley listed possible mechanisms in 1965, identifying weak effects from: bremsstrahlung from shower particles via the Coulomb field of atoms in the air; bremsstrahlung from low-energy electrons (δ-rays); transition radiation as the shower enters the ground; induction effects; and molecular transitions in the radio band. He considered charge separation giving rise to dipole Cherenkov radiation and synchrotron radiation from electrons curving in the Earth's magnetic field more important, as well as Cherenkov radiation from a charge excess as suggested by Askaryan (1962). Kahn and Lerche (1966) were the first to show the relative importance of the magnetic field in determining the intensity of the radio pulse. Three components of the emission were identified: the current mechanism as the electrons are deflected by the Earth's field (essentially the synchrotron mechanism); the dipole Cherenkov radiation; and the charge excess Cherenkov. The current (synchrotron) mechanism was found to give the most intense pulses. Colgate (1967) also calculated pulse intensities by equating the momentum carried by the pulse to that lost by the particles being deflected by the magnetic field. Fujii and Nishimura (1969) extended the Kahn and Lerche theory to include a finite shower thickness and Spencer (1970) included the effects of an idealized lateral distribution in the shower front. Modern calculations use the much more realistic Monte Carlo cascade models of the development of cosmic-ray air showers (CORSIKA) and microscopic models for the radio emission. The Earth's magnetic field has a dip angle (inclination) of 68° at Jodrell Bank. Because the radiated pulse amplitude is proportional to the sine of the angle between the electron trajectory and the field, we would expect a stronger signal from showers arriving from the north than the south. A right-angled double corner reflector was constructed by Porter using a vertical reflector oriented east–west with north and south reflectors fed by four half-wave dipoles separated by 0.5 wavelengths. An analysis of several thousand events showed that there was no significant difference between the strengths of pulses from the north or the south, though the results were consistent with an equal contribution from the charge excess and geomagnetic mechanisms (Porter et al. 1967). Porter also performed a polarization experiment in which the south side of the main array was rotated by 90° with no significant effect, even after 50 days of measurements. As a result of these inconclusive experiments, it was decided to build more sensitive apparatus by using a phased radio array with twin beams, directed parallel and perpendicular to the Earth's magnetic field. It was also necessary to find the general direction of arrival of the air shower, and so the Geiger counters were replaced with scintillators, as shown in figure 4, and fast timing used to select showers coming from the north or south. In 1966, Tony Bray was given the task of designing and implementing the radio array, now operating at 42 MHz, while Porter built the trigger and timing electronics. The experiment ran in 1967, producing 2000 events. More strong events were seen in the northern beam, perpendicular to the magnetic field, showing that the geomagnetic effect predominates, though there was some evidence that weaker showers had an equal contribution from the charge excess mechanism (Bray 1969). 4 View largeDownload slide Diagram of a scintillator designed at AERE Harwell used for all experiments after the summer of 1966. The liquid scintillator consisted of medicinal liquid paraffin with p-terphenyl and POPOP as the active ingredients. High-voltage supplies in Blackett's Hut were connected via coaxial cable to the scintillators, as were the electronics to form event triggers. 4 View largeDownload slide Diagram of a scintillator designed at AERE Harwell used for all experiments after the summer of 1966. The liquid scintillator consisted of medicinal liquid paraffin with p-terphenyl and POPOP as the active ingredients. High-voltage supplies in Blackett's Hut were connected via coaxial cable to the scintillators, as were the electronics to form event triggers. The radio spectrum Ralph Spencer's interest in radio emission from cosmic rays was kindled by a talk given late in 1965 by Jelley to physics undergraduates at the University of Birmingham. He joined the new MSc course in Radio Astronomy at Jodrell Bank in October 1966. He chose cosmic-ray work for his thesis project and then for his PhD. To his surprise, the first duty of a new student was to have a fitting for wellington boots and then to dig post holes. The particle detector array covered the whole of the field (figure 5), and the outputs of the photomultipliers were connected back to the discriminators and coincidence unit in Blackett's Hut through 300 m of coaxial cable. The scintillators were arranged as two equilateral triangles of side 50 m and a central square of the same half-diagonal as the distance from a vertex to the centroid of the triangles. The central square was used for the fast timing. Slow coincidences (2 μs) were also used, and a trigger was produced if either of the triangles or the square array produced a coincidence. The trigger combination was displayed on a hodograph array of light-emitting diodes in the oscilloscope camera, giving a rough indication of the location of the shower. Shower sizes were estimated to be a few multiples of 105 particles for the triangle and square arrays, and 3 × 106 particles for the whole array, corresponding to a primary energy between 1015 and 1016 eV. Figure 5 shows the layout of the equipment in the field at this time. 5 View largeDownload slide Arrangement of scintillators and radio aerials in the field adjacent to Blackett's Hut in 1966. The small circles denote the positions of the scintillators, with the triangle and square symbols representing the coincident trigger arrangements. The equilateral triangle arrays of detectors had spacings of 50 m on each side. The Polar Axis Telescope was used for lunar radar during these experiments. 5 View largeDownload slide Arrangement of scintillators and radio aerials in the field adjacent to Blackett's Hut in 1966. The small circles denote the positions of the scintillators, with the triangle and square symbols representing the coincident trigger arrangements. The equilateral triangle arrays of detectors had spacings of 50 m on each side. The Polar Axis Telescope was used for lunar radar during these experiments. The aim of the experiment was to investigate the radio spectrum of the pulses. We realized that coherence would be lost as the wavelength approached the shower thickness, meaning that the radiation intensity would be expected to be much lower at, say, 300 MHz than at 40 MHz. There would also be a more rapid fall off with frequency at large lateral distances from the shower core as a result of geometric effects. We needed to confirm this and perhaps find the optimum frequency for detecting large showers. The first task was to design a receiver for use at 105 MHz, just above the FM broadcast band, again working on the assumption that it would be quiet at night! A small 2λ by 2λ array of half-wave dipoles was built. Later experiments at 240 MHz and 408 MHz used a 9 m diameter parabolic wire-mesh dish originally built for a demonstration at the Festival of Britain in 1951. Calibration was via careful measurement of the noise performance of the receivers including the effects of the Milky Way galaxy, but the antenna gains were estimated from theory. We examined 4000 photographs but did not see any strong pulses. Most of the analysis was done by pulse counting, where the position of the strongest signal in each trace was noted. The most common position was at the expected time delay along the trace. The results (Spencer 1969, 1970) showed a steep spectrum for the emission with the field strength of the pulses falling off as E ∼ f–1, after correcting for bandwidth, which is in agreement with later work. There was some evidence that the more distant showers were relatively weaker at the higher frequencies, though indeterminate shower size selection effects were important. What was clear is that the signal-to-noise ratio was close to optimum at ∼30–40 MHz, clearly justifying our original assumptions. The Hafren experiment The detection of large extensive air showers by radio means alone poses a number of problems. Observers need to be able to detect broadband pulses, in a heavily used frequency band, and to be able to find the direction to a reasonable accuracy. A radio-only timing experiment was needed in a radio-quiet site away from populated areas. In 1969, the Jodrell group decided to try an experiment using four broadband conical antennas operating between 30 and 60 MHz, and to trigger an oscilloscope and recording camera using coincidences between pulses from the spaced antennas. The signals from each antenna were delayed in steps of 1 μs, and the oscilloscope triggered four times in order to show the signal from each antenna in turn. The relative timing of short pulses could then give an indication of the direction to an accuracy of 5–10° in azimuth and ∼10° in elevation. A camera with continuously moving film recorded the oscilloscope display. The running speed and film cassette capacity allowed unattended operation for more than a week. A two-channel chart recorder monitored the coincidence unit output and the automatic gain control (AGC) output of one channel. After commissioning the antennas and electronics at Jodrell Bank, the equipment was moved to a clearing in Hafren Forest (figure 6), on the side of Plynlimmon in mid-Wales – which certainly counted as a remote site, requiring a five-hour journey from Cheshire in a four-wheel-drive vehicle. 6 View largeDownload slide The Hafren experiment. (Left) The equipment trailer on the site labelled Sheep Dip on the Ordnance Survey map. (Right) One of the four monopole conical antennas. The radiating element was a set of wires (not visible in the picture) connected from the upper frame down to a balun transformer on the ground. 6 View largeDownload slide The Hafren experiment. (Left) The equipment trailer on the site labelled Sheep Dip on the Ordnance Survey map. (Right) One of the four monopole conical antennas. The radiating element was a set of wires (not visible in the picture) connected from the upper frame down to a balun transformer on the ground. The equipment was run for two years, mostly through the summer, after operations in the first year showed that access in the winter on forest tracks was somewhat limited. The equipment was checked and films collected once per week. Early results showed that the site was indeed relatively radio quiet with Band 1 TV signals from distant (Spanish TV) transmitters only being detected in anomalous ionospheric conditions. What was also clear was that there were several types of events, the majority not being the bandwidth-limited narrow pulses that we expected from cosmic-ray air showers. Interference levels, though much weaker than at the Jodrell Bank site, were nevertheless problematic (Porter et al. 1973). A comprehensive analysis was done by Chris Rapley for his MSc thesis (Rapley 1970). Based on an estimated collecting area for the array of ∼2 × 104 m2, and an estimated detection threshold of ∼1017 eV, the anticipated event rate was ∼15 air showers per week. This calculation was approximate, and did not take into account the sky-limited night-time variations of the automatic gain control, nor the reduction in gain and observing time lost through daytime TV transmissions and radio interference. The antenna polar diagrams with a half power point at approximately 35° and a zenith null also reduced the sensitivity to air showers from high elevation angles. Puzzling pulses In practice, analysis of five weeks of data collected in the autumn of 1969 showed rates ∼105 pulses per week, far more than expected. The events were found to fall into three general classes. The first dominated the records, with ∼8 × 104 counts per week. They were detected at high rates over long periods at night when the system sensitivity was highest, and more sporadically at other times. The pulses had characteristic shapes, with fixed but apparently impossible inter-channel delay times, except in one channel where the pulse delay was sporadic. This was puzzling, until it was realized that a source solution could be found within the array, coincident with the diesel generator to within a few metres. The sporadic pulses occurred in a channel with an antenna obscured from the generator by a ridge, modulating the system triggers by multipath or random detections. The interference commenced after a known problem with the generator, and could have been eliminated had the problem been picked up and understood during the deployment. The delay in the processing and analysis of the film records, plus the occurrence of the pulses at times when the system was unattended, militated against this. The second class of events occurred in large-amplitude bursts of ∼1 min duration during the working day. They occurred on average about 20 times a week, and contributed ∼2 × 104 counts to the total. Source directions were found to coincide within the uncertainties with local farms and tracks and a ploughed field lying between 1500–3000 m of the array, and were attributed to electrical interference from vehicles and machinery. Three bursts originated from the sky, one of which tracked from an elevation of 0 to 60° in ∼30 seconds; these were attributed to aircraft or helicopters. The third class of events contributed on average ∼400 pulses per week, most of them in low rate (<2 per minute) groups of between 2 and 150 low-amplitude pulses, with random relative delays, mostly during the working day. These also were attributed to weak electrical interference. We also considered the possibility of picking up electrical discharges (St Elmo's fire) from the pine needles of the forest, but a laboratory experiment gave a null result. No electrical storms were reported during the observing period. One single bandwidth-limited pulse was detected on 31 August 1969 at 02.12 UT and was attributed to an ∼1017 eV air shower at 30° elevation. Based on this experience of the difficulties of running a remote site without the benefit of online monitoring, and analysis of the results of the Hafren experiment, we decided to redeploy the array on site at Jodrell Bank. Improvements were made to the AGC and threshold discriminators, and the ability to operate with selectable three-fold rather than only four-fold coincidence introduced. We located one antenna in a small copse, and the others on open ground, allowing any effect of obscuration by trees to be investigated; none was found. However, the main innovation here was the development of a real-time display of source azimuth and elevation on the oscilloscope. We obtained mean daily pulse totals an order of magnitude greater than at Hafren. However, a direct numerical comparison is misleading given the saturating effect of the BBC1 television signal during the day. In reality, the Jodrell environment was very much noisier. Approximately one-third of each day's total pulses occurred between the hours of 3.30 and 7.30 UT, when the system was still sky- rather than television-limited. The preceding four hours could be relatively free of interference, containing only ∼25 pulses, although on some nights high levels of interference continued non-stop. For operational reasons and lack of time, it was not possible to develop and analyse the film records. But visual analysis of the oscilloscope display showed correlations of pulses with passing vehicles and as many as 90% of events at zero elevation. More interesting were signals observed during a series of heavy thunderstorms, in which pulse rates of 100s per second were observed in multiple bursts lasting several seconds with source directions associated with visible thunderheads. Most bursts terminated in a sudden rapid change of direction. On occasion, several sources were detected simultaneously and were seen to streak in different directions across the sky. One researcher's noise is another's signal, and it was concluded that while atmospheric electrical storms place a limit on air-shower observations, they provide an interesting source of information in their own right. We note that the atmospheric electric field strongly affects the radio emission from extensive air showers (Mandolesi et al. 1974, Buitink et al. 2007) – indeed air showers may even initiate lightning strikes (Dubinova et al. 2015). We did, however, notice that the electromagnetic pulse from nearby lightning strikes triggered the particle detector array at Jodrell Bank through pick-up on the cables, and produced detectable signals in the radio receivers, so the situation may be confused. The outcome of the Hafren experiment was to underscore the difficulties of achieving interference-free observations even at a remote site, but also to demonstrate that, even at a much noisier site such as Jodrell, some limited periods – a few hours per day – of viable operation could be achieved. The sources are as follows: aircraft, helicopters (and these days – drones); satellites; ionospheric reflections; atmospheric electrical activity; random noise pulse combinations, cosmic sources; cosmic-ray air showers. A renaissance Active work on the radio emission from cosmic rays diminished after 1975, with few papers published in the following 30 years (Weekes 2001, Huege 2016). But a November 2000 meeting in Los Angeles on the radio detection of high-energy particles (Salzberg & Gorham 2001) led to a revival of interest in the subject (see review by Huege 2016). The use of digital techniques made sophisticated experiments possible (Falcke & Gorham 2003) in which signals from many antennas could be processed. The new experiments include CODALEMA (Ardouin et al. 2005), LOPES (Falcke et al. 2005), the Auger Engineering Radio Array (AERA, Schulz 2015), LOFAR (Schellart et al. 2013) and Tunga-Rex (Bezyazeekov et al. 2015). There have also been major developments in the theory of the radio emission mechanism, with microscopic approaches following the tracks of individual particles. The geosynchrotron approach has been found to be incorrect because the particle tracks are relatively short as a result of interaction with air molecules. Modern codes such as CoREAS and ZHSAires use the results from Monte Carlo shower simulations (reviewed by Huege 2016) and show good agreement with experimental results. Over the past decade, the radio technique has become a mainstream addition to particle arrays for the study of cosmic rays with energies greater than 1017 eV. Since the radio emission depends on the longitudinal dependence of the shower, radio methods can be used to indicate the composition of the primary particles (e.g. Buitink et al. 2016). The fact that radio antennas and receivers are relatively inexpensive means that large areas can be covered even though the radio footprint of the showers is only a few hundred metres in diameter. Perhaps the most exciting prospect is the measurement of the composition of cosmic rays of energy 1017–1018 eV with high precision using the SKA Low Frequency Array to be built in a radio quiet zone in Western Australia (Huege et al. 2017). Development of a scintillator particle detector to trigger data collection from the many antennas in the array is currently taking place at Jodrell Bank. Conclusion Many of the basic characteristics of radio emission from extensive air showers were found by the early research, through sometimes heroic efforts. Now much has changed, mainly as a result of the use of digital technology, which has enabled automatic analysis from many antennas and realistic theoretical modelling. Recent experiments have tended to concentrate on showers with energies of >1017 eV, well above the threshold for the experiments in the 1960s. The radio signals are strong and easily detectable by single dipole antennas. Our early experiments therefore suffered from a lack of suitably strong events – which explains why so many triggers had to be detected before events with good signal-to-noise ratios were found. The accuracy of modern measurement is much superior to that in the 1970s and the use of radio has now become an essential addition to the armoury of techniques for the study of cosmic rays. ACKNOWLEDGMENTS The authors thank Sir Francis Graham-Smith and Justin Bray for valuable comments on the manuscript. REFERENCES Allan H R 1971 Progress in Elementary Particle and Cosmic Ray Physics X 171 Ardouin D et al. 2005 Nucl. Instr. Meth. A 555 148 CrossRef Search ADS Askaryan G A 1962 Sov. Phys. J. E. T. P. 14 441 Bezyazeekov P A et al. 2015 Nucl. Instr. Meth. A 802 89 CrossRef Search ADS Blackett P M S & Lovell A C B 1941 Proc. Roy. Soc. 177 183 CrossRef Search ADS Bray A 1969 Nature 223 723 CrossRef Search ADS Buitink S et al. 2007 Astron. & Astrophys. 467 385 CrossRef Search ADS Buitink S et al. 2016 Nature 531 70 CrossRef Search ADS PubMed Colgate S A 1967 J. Geophys. Res. 72 4869 CrossRef Search ADS Dubinova A et al. 2015 Phys. Rev. Lett. 115 015002 CrossRef Search ADS PubMed Falcke H & Gorham P W 2003 Astropart. Phys. 19 477 CrossRef Search ADS Falcke H et al. 2005 Nature 435 313 CrossRef Search ADS PubMed Fegan D 2012 Nucl. Instr. Meth. A 662 S2 Fujii M & Nishimura J 1969 Proc. IUAP Conf. Cos. Rays. Budapest 69 Gorham P 2001 in eds Salzberg D & Gorham P AIP Conf. Proc. 579 253 Hess V E 1911 Physik Z 12 998 Huege T C 2016 Phys. Rep. 620 1 CrossRef Search ADS Huege T C et al. 2017 EPJ Web. Conf. 135 02003 CrossRef Search ADS Jelley J V 1958 Cerenkov Radiation and Its Applications ( Pergamon Press ) Jelley J V et al. 1965 Nature 205 327 CrossRef Search ADS Jelley J V et al. 1966 Nuovo Cim. 46 649 CrossRef Search ADS Kahn F D & Lerche I 1966 Proc. Roy. Soc. A 289 206 CrossRef Search ADS Lovell B 1968 The Story of Jodrell Bank ( Oxford University Press ) Lovell B 1975 Biogr. Mems Fell. R. Soc. 21 1 CrossRef Search ADS Mandolesi N et al. 1974 J. Atmos. Terr. Phys. 36 1431 CrossRef Search ADS Patrignani C et al. (Particle Data Group) 2016 The Review of Particle Physics Chin. Phys. C 40 100001 chapter 29 Porter R A 1967 unpublished MSc thesis (University of Manchester) Porter R A et al. 1967 Nature 213 110 CrossRef Search ADS Porter R A et al. 1973 J. Atmos. Terr. Phys 35 1421 CrossRef Search ADS Rapley C 1970 unpublished MSc thesis (University of Manchester) Salzberg D & Gorham P W (eds) 2001 Radio Detection of Higher Energy Particles AIP Conf. Proc. 579 Schellart P et al. 2013 Astron. & Astrophys. 560 A98 CrossRef Search ADS Schulz J for the Pierre Auger Collaboration 2015 Proc. 34th ICRC The Hague, The Netherlands PoS(ICRC)615 Spencer R E 1969 Nature 222 460 CrossRef Search ADS Spencer R E 1970 unpublished PhD thesis (University of Manchester) Weekes T C 2001 in Radio Detection of Higher Energy Particles eds Salzberg D & Gorham P AIP Conf. Proc. 579 3 © 2018 Royal Astronomical Society

Sephton, Mark A;Waite, J Hunter;Brockwell, Tim G

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty146

Mark A Sephton, J Hunter Waite and Tim G Brockwell look at the capabilities of the Europa Clipper mission to explore one of Jupiter's icy moons. Liquid water is recognized as a prerequ-isite for life on Earth and elsewhere. Many of the biochemical components in living organisms are water-soluble and water provides a medium in which biochemical reactions can take place. Furthermore, the phase transition temperatures of water are in the range where those reactions take place at reasonable rates. Other requirements for life are the availability of raw materials and a source of energy. Wherever liquid water persists in the solar system, the possibility of life is raised. Recently, the presence of liquid water has been suggested in the outer reaches of the solar system, within the icy moons of the giant planets including, in particular, the subsurface of Jupiter's icy moon Europa. The evidence for liquid water at Europa comes in the form of an induced magnetic signature that is consistent with a hidden liquid-brine ocean (Khurana et al. 1998) and the smooth surface of the moon suggests relatively recent resurfacing by fluids (Smith et al. 1979). Europa has a tenuous atmosphere formed by the sputtering of surface ices by charged particles trapped in Jupiter's magnetosphere (Hall et al. 1995), which is an order of magnitude stronger than Earth's. There is growing evidence that the europan atmosphere is also supplied by plumes (Roth et al. 2014). If habitable conditions exist in the subsurface ocean of Europa then there may be evidence of it in the atmosphere. The NASA Europa Clipper mission (figure 1) will launch sometime in the first half of the 2020s and will orbit Jupiter 45 times, taking repeated measurements of Europa's atmosphere (Phillips & Pappalardo 2014). The mission will last three-and-a-half years and will pass as close as 25 km from the surface of the moon. 1 View largeDownload slide Artist's impression of Europa Clipper passing Jupiter's icy moon. (NASA/JPL-Caltech) 1 View largeDownload slide Artist's impression of Europa Clipper passing Jupiter's icy moon. (NASA/JPL-Caltech) Europa Clipper instruments On board the Europa Clipper will be an instrument suite that can assess the habitability of Europa. The MAss SPectrometer for Planetary EXploration/Europa, called MASPEX (figure 2), is a high-resolution, high-detection-sensitivity multibounce time-of-flight instrument (Brockwell et al. 2016) capable of measuring trace species (at levels of parts per billion for organic compounds). Any gases, ices or organic molecules in Europa's atmosphere can be analysed by MASPEX either by direct analysis or by concentration of analytes in a cryotrap, which achieves greater sensitivities. 2 View largeDownload slide The MASPEX high-resolution mass spectrometry system. (SwRI) 2 View largeDownload slide The MASPEX high-resolution mass spectrometry system. (SwRI) MASPEX targets All known life is based on carbon-rich organic matter. Carbon can form chemical bonds with many other atoms, exhibits a great deal of chemical versatility and forms compounds that readily dissolve in water. The organic compounds to be detected by MASPEX can be intact molecules or parts of larger parent structures with fragmentation caused by radiolytic fracturing on the surface of Europa or by impact dissociation on the MASPEX antechamber walls. While the fragmentation process makes interpretation more complex, it also makes larger molecular structures more amenable to analysis. Fragmentation is, therefore, analogous to analytical pyrolysis, where organic networks such as those in biomolecules are unzipped by rapid heating. The rapid fragmentation of large organic networks is important because in living organisms, fossil remains of life, and non-biological macromolecules in meteorites it is the large organic networks that are quantitatively most important. Recognizing life with mass spectrometry Mass spectrometry is a common and effective method for the detection of organic compounds. When organic compounds are ionized, they dissociate and the fragments produced are characteristic of the starting molecular architecture. Mass spectrometry is most powerful when used at high resolution to discriminate between organic compounds of the same integer mass, but with different ratios of elements. For example, an integer mass of 178 can represent anthracene (C14H10), a common abiotic organic partial combustion product, which has an exact mass of 178.2292. But it can also indicate coniferyl aldehyde (C10H10O3), a biotic organic compound which has an exact mass of 178.1846. MASPEX operates in high-resolution mode and has the potential to distinguish between abiotic and biotic organic matter. Organic materials used by biology are designed to perform biochemical roles and their detailed structures are produced by enzymes. In the absence of biology, by contrast, organic synthesis processes lead to a relatively random assemblage of products. These characteristics can be recognized in mass spectra and have been used to discriminate between indigenous abiotic organic matter and terrestrial biological contamination in carbon-rich meteorites for decades. During random synthesis, more carbon atoms mean more potential isomers and the number of isomers increases in an exponential fashion with carbon number. For example, 10 carbon atom alkanes can have over 70 isomers, while 20 carbon atom alkanes could have over 350 000 isomers (figure 3). Biological enzyme-directed synthesis can result in all carbon atoms being used to produce a single organic isomer. 3 View largeDownload slide The rapid increase in potential isomers with increasing carbon number. Random non-biological synthesis will spread carbon among the various possible isomers. Biological synthesis is controlled by enzymes and will generate a limited number of specific organic structures with its carbon. 3 View largeDownload slide The rapid increase in potential isomers with increasing carbon number. Random non-biological synthesis will spread carbon among the various possible isomers. Biological synthesis is controlled by enzymes and will generate a limited number of specific organic structures with its carbon. Looking deeper If molecular architectures associated with habitable or inhabited conditions are detected, further and more sophisticated interpretations are possible through this technique. Although the type of life that may be encountered in the outer solar system is uncertain, it may be possible to identify whole ecosystems in operation. On Earth, the three domains of life can be recognized in mass spectra by characteristic ions. Isoprenoids (m/z 183), hopanoids (m/z 191) and steroids (m/z 217) represent the membrane molecules of Archaea, Bacteria and Eukarya respectively. A range of biomolecule types could potentially be detected on Europa as well. Although MASPEX is destined for Europa, it could also be used for similar missions to other icy moons. Ganymede (Kivelson et al. 2002) and Callisto (Kivelson et al. 2000) at Jupiter, and Enceladus and Titan (Spencer & Nimmo 2013) at Saturn also present evidence of subsurface liquid water. The cratering record of Enceladus also indicates recent resurfacing (Porco et al. 2006) and plumes can be observed erupting from it into space (Hansen et al. 2006, Waite et al. 2006). The icy moons of Jupiter and Saturn are providing new opportunities for scientists seeking to understand the origin and distribution of life in our solar system – and analytical instruments such as MASPEX offer the means to exploit those opportunities. REFERENCES Brockwell T G et al. 2016 The mass spectrometer for planetary exploration (MASPEX) 2016 IEEE Aerospace Conference (IEEE Computer Society) https://doi.org/10.1109/AERO.2016.7500777 Hall D T et al. 1995 Nature 373 677 CrossRef Search ADS PubMed Hansen C J et al. 2006 Science 311 1422 CrossRef Search ADS PubMed Khurana K K et al. 1998 Nature 395 777 CrossRef Search ADS PubMed Kivelson M G et al. 2000 Science 289 1340 CrossRef Search ADS PubMed Kivelson M G et al. 2002 Icarus 157 507 CrossRef Search ADS Phillips C B & Pappalardo R T 2014 Eos Transactions American Geophysical Union 95 165 CrossRef Search ADS Porco C C et al. 2006 Science 311 1393 CrossRef Search ADS PubMed Roth L et al. 2014 Science 343 171 CrossRef Search ADS PubMed Smith B A et al. 1979 Science 206 927 CrossRef Search ADS PubMed Spencer J R & Nimmo F 2013 Ann. Rev. Earth Planet. Sci. 41 693 CrossRef Search ADS Waite J H Jr et al. 2006 Science 311 1419 CrossRef Search ADS PubMed © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty130

ECOLOGY A project using astronomical tools and thermal imaging is helping to detect rare and endangered animals. A team of astronomers and ecologists from Liverpool John Moores University has combined machine-learning algorithms and tools for astronomical detection with thermal infrared cameras on drones (figure 1). The goal is an automated system that can find and track animals – and poachers. “We held a field trial in South Africa last September to detect riverine rabbits, one of the most endangered mammals in the world,” said Claire Burke (LJMU). “They are very small, but we managed five sightings. Given that there have only been about 1000 sightings ever, it was a real success.” The team has now modelled the effects of vegetation, so that they can detect animals hidden by trees or plants. Further field tests will look for orangutans, spider monkeys and river dolphins. 1 View largeDownload slide Large rhinos might be relatively easy to identify in infrared, but the project has had success with rare rabbits too. (Endangered Wildlife Trust/LJMU) 1 View largeDownload slide Large rhinos might be relatively easy to identify in infrared, but the project has had success with rare rabbits too. (Endangered Wildlife Trust/LJMU) http://bit.ly/2joh8zP © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty115

COPERNICUS With the launch of the Sentinel 3B Earth-observation satellite, Europe's Sentinel constellation of seven, part of Europe's Copernicus environmental monitoring network, is now complete. Sentinel 3 is directed at measuring the sea and ice surface. The data return is huge. “We get 14 Tb from the Sentinels alone,” said Joel Aschbacher (ESA) at the European Union of Geosciences meeting in Vienna in April. “That's more data from the Sentinels than is uploaded to Facebook per day.” http://bit.ly/1nPfa8T © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty123

View largeDownload slide View largeDownload slide AWARDS The winners of a new RAS competition came to the 9 March RAS Ordinary Meeting to present their posters and receive their prizes. The competition, sponsored by Winton Capital, was open to the 12 students who had taken the Edexcel Astronomy GCSE and achieved the highest marks nationally. They were invited to produce an A3 poster on an astronomical topic. The winner was Zachary Place (pictured middle, Marlborough College) who received £100 of book tokens, with runners-up Meg Savage (left, Farlington School, £50) and Daniel Leboff (right, JFS School, £25). All three were present to discuss their posters with those attending the RAS meetings and to chat; all demonstrated excellent command of their subjects. Zachary addressed the solar dynamo and the origin of active regions of the Sun, Meg tackled cosmic topology and WMAP results, and Daniel covered the hot topic of transit photometry. © 2018 Royal Astronomical Society

Bowler, Sue

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty098

View largeDownload slide View largeDownload slide EDITORIAL I am, of course, pleased that people read A&G, but I'm especially grateful to those 500-odd of you who responded to our Readers' Survey at the turn of the year. I asked for your impressions, opinions and criticisms of A&G – and you gave me plenty of food for thought. The comments alone ran to 63 pages! The headline news is that RAS Fellows value A&G: 75% of respondents considered it an important benefit of Fellowship and a further 10% as the most important benefit. That's 85% who value A&G highly. I also found out that most people read the print issue of A&G, and prefer to do so. Some of those who commented were unaware that they can read A&G online, for free. Just to be clear: all Fellows have online access to the Society's publications, including Monthly Notices and Geophysical Journal International; for A&G there is even a full-issue pdf file that you can download. I'm grateful for your suggestions for topics and areas to cover – these are always welcome. I also liked to read about likes and dislikes. I was pleased that there were more of the former than the latter, but one person's favourite often popped up as someone else's pet hate! But there were excellent ideas that we hope to follow up in the coming months. Thank you once again for all the comments, criticisms and compliments. If any more occur, don't hesitate to get in touch. A&G is designed as a benefit to Fellows, but we benefit hugely from the work of Fellows too! © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty135

BLACK HOLES Gravitational wave detections carry information that can reveal how some binary black holes systems form. Joseph Fernandez (Liverpool John Moores University) presented simulations of close encounters between binaries and black holes like that at the centre of our galaxy. Most of the time the tidal effects simply disrupted the binary systems. But some encounters gave them radically different orbits, that would lead them to merge much sooner than otherwise. The simulations produce negative effective spins, in which the black holes are orbiting in the opposite direction to their initial configuration. “Negative effective spins are smoking-gun signs that the binary in question originated from a dynamical formation channel, like the one we have described,” said Fernandez. “If you can characterize what distribution of effective spins a mechanism would generate, and the rate at which your mechanism can produce mergers, you can obtain an expected effective spin distribution and compare it with observations.” http://bit.ly/2rbQmPe © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty116

ALMA/APEX Teams using detailed data from the Atacama Large Millimetre/submillimetre Array (ALMA) and APEX, the ALMA Pathfinder Experiment, have each resolved a clump of galaxies in the process of forming a galaxy cluster. The protoclusters SPT 2349-56 and DRC (14 and 10 galaxies) are much older than expected; the galaxies are surprisingly large and forming stars. The data come from 1.5 billion years after the Big Bang, before models suggest such large galaxies could assemble, challenging cosmological models. Miller et al. published in Nature, Oteo et al. in The Astrophysical Journal. http://bit.ly/2jnKYnG © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty110

ALMA The proportions of more massive to less massive stars have been considered fixed at birth – the initial mass function – because young stars and star-forming cores in molecular clouds close to the solar system share the pattern. Now observations with the Atacama Large Millimetre/submillimetre Array of a more distant and perhaps more typical star-forming region, W43-MM1, suggest that this is not the case: more massive star-forming cores there were much more abundant than the accepted model would suggest, and less massive ones less common. http://www2.cnrs.fr/en/22.htm © 2018 Royal Astronomical Society

Macdonald, Sofie;Stevens, Adam

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty145

What could autonomous aircraft do for planetary exploration? Sofie Macdonald and Adam Stevens set out the potential and pitfalls of extraterrestrial drones. The technology used to explore planetary surfaces has progressed rapidly from wire-guided squat rovers the size of a toy – the Mars 3 Prop-M rover, landed by the Soviet Union in 1971 but not deployed – to nuclear-powered rovers the size of cars, armed with an array of cutting-edge instruments – NASA's Mars Science Laboratory, currently exploring Gale Crater. Now, research is being carried out to design aerial vehicles able to function in the alien environments of our solar system. The Mars 2020 Rover may carry a scout helicopter (figure 4), while Dragonfly, a vertical-takeoff and landing (VTOL) vehicle designed to explore Saturn's moon Titan (Lorenz 2017), is one of two proposals in the final round of selection for NASA's New Frontiers programme (figure 1). 1 View largeDownload slide The Dragonfly rotorcraft arrives on the surface of Titan then takes off for the first time. In December 2017, Dragonfly was one of two mission proposals chosen by NASA to receive investment as part of its New Frontiers selection programme. The dense, calm atmosphere and low gravity make flying an ideal means to travel on Titan. In a single flight of up to an hour, Dragonfly could fly a few tens of km, further than any planetary rover has traveled, and could explore sites several hundred km away within the planned two-year mission duration. However, Dragonfly would spend most of the time on the surface making science measurements. Unable to use solar power under Titan's hazy atmosphere, Dragonfly would use a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) like the Curiosity rover on Mars. Flight, data transmission and most science operations would be planned during Titan's day (8 Earth days), with plenty of time during the Titan night to recharge. http://dragonfly.jhuapl.edu (Johns Hopkins APL/Steve Gribben) 1 View largeDownload slide The Dragonfly rotorcraft arrives on the surface of Titan then takes off for the first time. In December 2017, Dragonfly was one of two mission proposals chosen by NASA to receive investment as part of its New Frontiers selection programme. The dense, calm atmosphere and low gravity make flying an ideal means to travel on Titan. In a single flight of up to an hour, Dragonfly could fly a few tens of km, further than any planetary rover has traveled, and could explore sites several hundred km away within the planned two-year mission duration. However, Dragonfly would spend most of the time on the surface making science measurements. Unable to use solar power under Titan's hazy atmosphere, Dragonfly would use a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) like the Curiosity rover on Mars. Flight, data transmission and most science operations would be planned during Titan's day (8 Earth days), with plenty of time during the Titan night to recharge. http://dragonfly.jhuapl.edu (Johns Hopkins APL/Steve Gribben) But why are drones so attractive for planetary exploration? To date, reconnaissance of planetary exploration sites has been achieved by orbital survey. An orbital platform can use cameras, altimeters and spectrometers to map the terrain and features of wide regions of a planet. Some say that we have a better understanding of the surface of Mars than the Earth's ocean due to the incredible work of orbiters such as Viking, Mars Global Survey, Mars Express, Mars Odyssey and MRO and their suites of instruments looking across the electromagnetic spectrum. Cutting-edge technology has driven resolution to the point where the Hi-Rise instrument on the Mars Reconnaissance Orbiter can image features as small as 25 cm (McEwen et al. 2007). On the other hand, Mars rovers now carry incredibly high-resolution instruments that can produce highly detailed surveys of the area around them and use advanced autonomous navigation systems to avoid obstacles without intervention from Earth. Yet a rock 24 cm across and invisible to an orbiter can cause a problem for a rover. Alternatively, it might be an ideal science target. The rover team won't know which until the rover travels close enough to find out, but rovers travel so slowly that it took Opportunity rover 14 years to cover 45 km. So much of planet Mars remains unexplored. This is where drones or, more formally, unmanned aerial vehicles (UAVs), come in. UAVs can cover large areas relatively quickly and can collect samples from wider areas that would be impossible to reach with the limited mobility of rovers. Drone-based imaging systems would have greater resolution than orbiters and cover more ground than rovers, taking close-up images over wide distances. Their access to both the air and the ground makes it possible to sample a planet's atmosphere for analysis, while also scanning the surface composition, and do both at different places separated by greater distances than reachable by rover. UAVs are ideal to plug the gap between orbiters and rovers in our knowledge of other planets and could act in concert with another mission, as a scout for a rover in the Mars 2020 mission, for example, or as a standalone platform, as in the Dragonfly proposal. The first, and so far only successful, planetary UAV mission was the Venus Vega balloons (figure 2). These two Soviet probes each carried a small balloon that was discharged into the atmosphere of Venus in 1985. Both balloons lasted only about two Earth days (Preston et al. 1986), providing data on wind speeds and the nature of atmospheric circulation at Venus. Since then, a wide range of aircraft have been proposed for incorporation into planetary missions. Proposals for Mars alone have included one-shot, disposable, drop from orbit, fixed-wing aircraft; trios of formation-flying gliders; lighter-than-air balloons or airships (Vargas et al. 1997); and several different VTOL rotorcraft (helicopters; Young et al. 2002). Similarly, a wide range of proposals have been made for missions to Venus and Titan, and even for missions to the gas giants, but none has made it beyond the concept stage. 2 View largeDownload slide The Russian Vega balloon mission to Venus, on display at the Udvar-Hazy museum. (G A Landis) 2 View largeDownload slide The Russian Vega balloon mission to Venus, on display at the Udvar-Hazy museum. (G A Landis) Design While the utility of aerial vehicles for planetary exploration might go without saying, designing such an aircraft to work on a different planet poses significant challenges. The most obvious factor that must be considered is the atmosphere. Here at the surface of Earth our atmosphere has a density of around 1.2 kg m−3 (varying with the weather), which imposes a pressure of roughly 101 kPa and is defined as 1 atmosphere (atm). This places a particular set of requirements on aircraft, which use wings, rotors or balloons to generate lift that can overcome gravity (see box “Aerofoils and balloons”). Many aircraft also use aerofoils for steering and propulsion. However, 1 atm is not a constant across the solar system, or even in our own atmosphere, which becomes less dense with altitude. To operate under different atmospheric conditions, aircraft must be designed with the appropriate conditions in mind. The amount of lift, L, generated by an aerofoil can be calculated by L=0.5ρν2SCL (1) where ρ is the atmospheric density, v is the airspeed, S is the wing area and CL is the lift coefficient, which varies depending on the angle of the aerofoil, the Mach number (a measure of the airspeed relative to the speed of sound) and the Reynolds number (a measure of turbulence) (Anderson 2007). Equation 1 provides a good rule of thumb for designing aircraft, though of course it doesn't incorporate all the subtleties of aeronautical engineering. If we keep all things the same, but reduce the atmospheric density by half, then an aerofoil generates roughly half as much lift. Double the airspeed – quadruple the lift (though drag must also be taken into account). Double the wing area – double the lift (though structural rigidity becomes a concern). Aerofoils are designed with a particular set of conditions in mind. When an aeroplane is taking off or landing, it is moving significantly slower and through atmosphere at higher density than it experiences at its cruising altitude, which is why you can see the wing changing shape if you peer out of the window at the beginning or end of your flight. On other planets, the environment is even more different from on Earth than the change between the Earth's surface and airline cruising altitude. At the surfaces of the three planetary bodies in the solar system with a substantial atmosphere, the atmosphere of Mars is approximately 100 times less dense (Leovy 2001), that of Titan approximately the same density as Earth (Mitchell & Lora 2016), and at Venus approximately 100 times more dense (Bullock & Grinspoon 1996). However, atmospheric density is not the only thing that changes – we must also take into account the gravitational attraction of the different bodies and balance this against any change in lift. Roughly speaking, Mars has a third of the gravity of Earth, Venus the same and Titan 10 times less. If we take this into account, an aircraft of similar design can carry around 30 times less mass on Mars, or would need to be 30 times more efficient or have a 30 times larger wingspan to carry the same mass; that design would carry 10 times more mass on Titan and 100 times more on Venus. These factors provide a foundation for designing aircraft for use on other planetary bodies, but there are many others that must be considered. For example, given that there are currently no extraterrestrial runways, aircraft for all extraterrestrial bodies would need the ability to take off and land vertically, or to stay aloft permanently. Fixed-wing aircraft are not good at vertical take-off and landing, which means that proposals tend to be rotorcraft or hybrid vehicles with some fixed-wing and some vertical rotor elements. Using rotors for lift has the benefit of reducing the size of the vehicle, which cuts the need to “fold” any wings into a rocket aeroshell for transport from Earth; a possible disadvantage is that rotorcraft can carry less mass than a fixed-wing aircraft of the same size and require more power to stay aloft. Generally this means that potential aircraft for Mars would have severely limited payloads, but the high atmospheric density of Venus and low-gravity environment of Titan make them attractive targets for aerial vehicles. Control The intricacies of flight and the fast reaction times required to adapt to changing atmospheric conditions mean that aerial vehicles on other planets will need their own autonomous control systems. The vehicles will need to take off, navigate, take measurements and land with potentially pinpoint precision, all without direct control from Earth; communication delays make this impossible. While autonomous control systems are becoming commonplace here on Earth – you can buy drones boasting complex autonomous control on the high street – and rovers are incorporating more and more autonomous navigation (Bajracharya et al. 2008), flying around other planets presents a significantly bigger challenge. In particular, Mars, Venus and Titan all experience extensive storms that are considerably more unpredictable than those on Earth (Delitsky & Baines 2015, Schaller et al. 2009, Wang & Richardson 2015). Avoiding such storms would be imperative for any aerial vehicle. Aerofoils and balloons A wing-shaped body (aerofoil) moving through a fluid generates an aerodynamic force perpendicular to its motion. In the case of a wing, this force acts as lift, allowing a vehicle to fly. The lift produced by an aerofoil is almost “free”, requiring only that the aerofoil is moving fast enough to generate more lift than the weight of the vehicle. Helicopter rotors work in the same principle, with a number of “wings” rotating around a central point to lift the vehicle or, when tilted or rotated in particular ways, to thrust the vehicle forwards or steer it in a particular direction. Aircraft propellers work in the same way, but are generally devoted to providing thrust. Wings and rotors are both energy-efficient methods of flight compared to a rocket engine or similar, but rely on the atmosphere being dense enough to provide lift. Balloons, on the other hand, provide lift using a compartment of gas that has a lower density than the atmosphere around it, making the entire vehicle buoyant. This can be achieved either by using a sealed container of gas with lower density than the atmosphere, such as hydrogen or helium, or by heating the ambient atmosphere inside a semi-closed container, such as in hot-air balloons. Montgolfière balloons, named for the inventor of the hot-air balloon, use passive solar heating, making them incredibly simple. 3 View largeDownload slide Examples of aerofoil profiles in Nature and in various vehicles. 3 View largeDownload slide Examples of aerofoil profiles in Nature and in various vehicles. Materials Both Venus and Titan would also bring their own environmental challenges to the design of aircraft. Venus has a surface temperature of around 460 °C, high-speed winds, lightning and rain of concentrated sulphuric acid. Move away from the surface, where the temperature is lower, and you would end up flying through those same sulphuric acid clouds that were raining on you lower down. Titan is almost the opposite in some ways and similar in others, with a frigid surface at −180 °C, but also high-speed winds and potentially hazardous substances raining from a cloud layer. In this case though, the clouds and rain are formed of liquid hydrocarbons. Extremes of temperature are a problem for electronics, especially when tied to mass limits for launch from Earth. In a hot environment, the electronics must be cooled, adding mass to your system. In a cold environment, the electronics must be warmed, adding mass to your system. Aircraft designed for Venus or Titan will need dedicated and powerful temperature control systems, but must also be built from materials that are capable of withstanding super-high or super-low temperatures (Landis 2006). Temperature-resistant materials are no mystery to spacecraft engineers, but normally these materials are required to withstand rapid changes in temperature, such as experienced during launch. Both Venus and Titan have effective heat distribution in their atmospheres, so that they maintain a fairly even temperature everywhere, but the stresses and strains associated with wings and rotors are unlike those faced by spacecraft outside an atmosphere: the materials must not be too brittle in the cold of Titan or too flexible in the heat of Venus, or the aerodynamic properties of the aircraft structure would be affected. Aluminium and titanium are standard materials in the aerospace industry; they might not be the best choices for the extremes of Venus or Titan. Other alloys often employed for high-temperature uses in aerospace are based on nickel and iron, but these may one day be replaced by molybdenum or tungsten. Molybdenum is often used as a coating on the outer parts of spacecraft to shield less heat-tolerant materials against the extremely high temperatures generated during re-entry through the atmosphere. It has one of the highest melting points of all elements while being significantly lower density than other high-melting point metals. In addition, its very low coefficient of thermal expansion, as well as its high thermal conductivity, make it well suited for use in very-high-temperature environments. Beryllium copper and similar alloys are of interest to the aerospace industry because they possess high strength and hardness, excellent wear and fatigue resistance, and good corrosion resistance, as well as good thermal and electrical conductivities. Carbon fibre materials are used in aerospace because of their low density but high strength and stiffness. However, some of their properties make them unsuitable for aircraft to fly on Venus or Titan. In particular, the standard resins used to fix carbon fibre materials are not resistant to heat, acid or hydrocarbon solvents and can simply melt or dissolve, losing structural support for the fibres. In addition, carbon fibres can be extremely brittle at the low temperatures encountered on Titan. The high concentration of sulphuric acid present throughout the atmosphere of Venus is a problem for several materials; even pure aluminium, which is typically resistant to corrosion, undergoes fairly extreme chemical reactions after long periods in concentrated sulphuric acid. All of this suggests that when designing aircraft for extraterrestrial exploration, we can't just fall back on standard aerospace techniques and materials but should instead design with care for the specific environment that we aim to explore. Venus and Titan present extreme environments that will be a challenge for any engineer to design for, whereas Mars is slightly more benign, although the low atmospheric density means aircraft designs will need to be very efficient in order to carry any kind of useful payload. Power Power is a major issue for aerial vehicles. Solar power is not an option for aircraft under the thick haze of Venus or Titan; they would have to rely on radioisotope thermal generators (RTGs, described by O'Brien et al. 2008). These are relatively heavy, reducing the mass available for the payload. They also give off a lot of waste heat. On Titan this waste heat could be used effectively to keep the rest of the aircraft warm, as is intended in the design for Dragonfly, but on Venus it would be a serious liability. On Mars, an aircraft could use solar power, as a number of rovers have done, but to do so would require a reasonable surface area for solar panels. On a helicopter, there would be limits on space for solar panels but on a fixed-wing aircraft, the wings could feasibly be covered in solar panels. An aircraft for Mars could also use an RTG, but the martian atmosphere imposes strict limitations on aircraft mass – carrying an RTG would probably use up a majority of any available payload mass. Another limitation of solar power would be that, unless the power was managed exceptionally well, the aircraft would need to land at night. As the highest power requirements for any aircraft would be during take-off and landing, our Mars aircraft would need to charge for part of the morning, before taking off and using stored power to travel, leaving enough power to land safely. Such a schedule limits the amount of exploration possible. There aren't many other power sources available for aerial exploration vehicles; one option would be to operate solely on batteries charged before arriving at the planet itself. This would limit the lifetime of the vehicle, perhaps only allowing it one flight – and such a mission would not really be exploiting the benefits of using an aerial vehicle in the first place. However, missions have been proposed with “fire-and-forget” aircraft, perhaps even launched from the upper atmosphere to allow them to glide long distances. There is also the option to use charging stations that stay in place on the surface of the planet (or are attached to a rover), but this would severely limit the range of an aircraft. Other vehicles So far, we have only considered traditional aircraft that use rotors or fixed-wings. These make most effective use of an atmosphere for lift, but are not the only options. Science fiction has inpsired suggestions that the thick atmosphere and low gravity of Titan would allow humans to use wingsuits and flap like birds, providing enough power to stay aloft. This concept could be extended to unmanned vehicles (ornithopters) as well. Although technically feasible, it's not obvious what benefits such a design would have over fixed-wing or rotor vehicles. 4 View largeDownload slide Artist's impression of the Mars Helicopter Scout. At the time of writing, trials were still being conducted and NASA had not decided whether the MHS will fly with the Mars 2020 mission. If it does, it will explore the terrain ahead of the rover, enabling it to drive up to three times futher each martian day. The helicopter would fly no more than three minutes per day and cover a distance of about 600 m. (NASA/JPL-Caltech) 4 View largeDownload slide Artist's impression of the Mars Helicopter Scout. At the time of writing, trials were still being conducted and NASA had not decided whether the MHS will fly with the Mars 2020 mission. If it does, it will explore the terrain ahead of the rover, enabling it to drive up to three times futher each martian day. The helicopter would fly no more than three minutes per day and cover a distance of about 600 m. (NASA/JPL-Caltech) Another technology that could be exploited is gas thrusters. These are used in aerial vehicles such as the Harrier Jump Jet and more modern F-35, where engine exhausts can be pointed downwards to provide lift. Similar techniques could be used in other planetary atmospheres, although this technique would be less efficient in the thin atmosphere of Mars. An extension of this technology would be to carry fuel for reaction mass, typically some kind of inert gas. This would allow thrusters to work more efficiently on Mars and even on airless bodies such as Europa, where aerial vehicles would otherwise be useful. However, the need to carry fuel would limit the lifetime of the vehicle and, as thrusters are not efficient, this would not be very long; this is why aircraft such as the Harrier rely on fixed-wing flight for long-distance travel. We could also look back to earlier aerial exploration and exploit the relatively simple engineering of balloons. These avoid many of the drawbacks of fixed-wing and rotorcraft, although they would depend on reliable mechanisms for unfurling the balloon material after long periods of spaceflight. Balloons could carry compressed low-density gases such as hydrogen or helium to use in their envelopes, or use Montgolfière principles with heaters or passive solar heating. Propulsion could come from relatively small propellers, which would require little energy because there would be no requirement to move the vehicles as fast as a fixed-wing equivalent in order to stay aloft. Alternatively, balloons could be allowed to drift freely, measuring weather systems passively. A simple system would be a passively heated Montgolfière balloon with a small instrument package and no propulsion. Such a vehicle could easily collect data over large distances. Finally, there is no reason to restrict ourselves to only one design for aerial vehicles. Aeronautical innovation on Earth has brought about any number of hybrid vehicles that exploit the benefits and reduce the drawbacks of any one type of design. The environments of other planetary bodies might lend themselves even more to hybrid aerial vehicles, so we might see any combination of fixed-wing, rotors, balloons and ornithopters in future. Nor do we need to restrict ourselves to a single vehicle. Just as there have been proposals for missions including multiple smaller components, a fleet of small aerial vehicles would offer advantages over a single larger one, though with the obvious restriction on the size of instruments. However, with on-going miniaturization across all types of instrumentation, this is becoming less of a problem. Summary With the prospect of two potentially interplanetary aerial vehicles in the near future, the world of extraterrestrial aerial design is an exciting one. The JPL-designed Mars Scout Helicopter could soon be acting as an autonomous pathfinder for the Mars 2020 rover, and we may see more detail of the surface of Titan than ever before via the Dragonfly rotorcraft if it continues through NASA mission selection. The fate of both vehicles will be decided over the coming weeks and years but, even if unsuccessful, advancements in aeronautical engineering on Earth make the prospects of aerial vehicles on other worlds that can map wider areas than rovers and in more detail than orbiters an obvious feature of the exploration of our solar system. REFERENCES Anderson J D 2007 Fundamentals of Aerodynamics ( McGraw-Hill ) Bajracharya M et al. 2008 Computer 41 ( 12 ) 44 CrossRef Search ADS Bullock M A & Grinspoon D H 1996 J. Geophys. Res. 101 ( E3 ) 7521 CrossRef Search ADS Delitsky M L & Baines K H 2015 Planet. and Space Sci. 113 184 CrossRef Search ADS Landis G A 2006 Acta Astronautica 59 570 CrossRef Search ADS Leovy C 2001 Nature 412 245 CrossRef Search ADS PubMed Lorentz R D 2017 Johns Hopkins APL Technical Digest http://dragonfly.jhuapl.edu McEwen A S et al. 2007 J. Geophys. Res. 112 E05S02 CrossRef Search ADS Mitchell J L & Lora J M 2016 Ann. Rev. Earth Planet. Sci. 44 : 1 353 CrossRef Search ADS O'Brien R C et al. 2008 J. Nuclear Materials 377 ( 3 ) 506 CrossRef Search ADS Preston R A et al. 1986 Science 231 ( 4744 ) 1414 CrossRef Search ADS PubMed Schaller E L et al. 2009 Nature 460 ( 7257 ) 873 CrossRef Search ADS PubMed Vargas A et al. 1997 Mars 96 Aerostat — an overview of technology development and testing, in AIAA International Balloon Technology Conference Wang H & Richardson M I 2015 Icarus 251 112 CrossRef Search ADS Young L A et al. 2002 Rotorcraft as Mars Scouts, in IEEE Aerospace Conference: Big Sky, Montana © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty114

YOUTUBE An immersive journey to six exoplanets has proved a huge outreach hit for the University of Exeter, with a million viewers since its launch on YouTube in late 2017. The virtual planet tour was made by a science team led by Nathan Mayne (University of Exeter), together with educational charity We The Curious and visual-effects artists from Engine House. As well as watching on-screen, the tour can be taken in virtual reality, if you have the headset. The tour includes Wasp-121b, with stellar winds blowing away its atmosphere, possible water world Kepler-62e and 55 Cancri e, so hot that its surface could be molten. http://bit.ly/2w8k10G © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty117

COSMIC VISION Ariel, the Atmospheric Remotesensing Infrared Exoplanet Largesurvey mission, was selected by ESA on 20 March as the next medium-class science mission, part of the Cosmic Vision programme. The mission has a strong UK presence, reflecting the strength of this field nationally. “ARIEL will study a statistically large sample of exoplanets to give us a truly representative picture of what these planets are like,” said principal investigator Giovanna Tinetti (University College London). STFC RAL Space will manage the overall European consortium building the payload, which will be assembled and tested in Harwell, Oxfordshire. Other UK involvement will come from Cardiff University, Oxford University and the UK Astronomy Technology Centre. http://bit.ly/2FA4kPs © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty122

View largeDownload slide Aerial image showing how the main active traces of the Hayward Fault (red lines) cut through part of the San Francisco Bay area. The main football stadium at the University of California, Berkeley (oval, centre), is nearly bisected by the fault and has been extensively retrofitted to withstand fault offset and shaking. (HayWired) View largeDownload slide Aerial image showing how the main active traces of the Hayward Fault (red lines) cut through part of the San Francisco Bay area. The main football stadium at the University of California, Berkeley (oval, centre), is nearly bisected by the fault and has been extensively retrofitted to withstand fault offset and shaking. (HayWired) DISASTER RECOVERY The US Geological Survey and the Seismic Safety Commission have published the results of a study simulating the effects of a major earthquake in California. As well as the direct seismic effects, the exercise included organizations responsible for managing the diverse secondary effects, such as public utility companies, emergency services, communications and community support. The outcomes reinforce the importance of collaboration and communication. The HayWired Earthquake Scenario was named because it simulated a M7.0 quake on the Hayward fault. The name also reflects the significance of the effects of a quake on communications, notably electrical and telecoms wires and optical fibres. The scenario used data from recent Californian quakes to assess aftershocks and soil liquefaction and from damaging quakes elsewhere such as that in Nepal in 2015. The goals were to build resilience among the communities and businesses – including many Silicon Valley technology giants – likely to be affected by such a quake. http://on.doi.gov/2rdc0me © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty124

MAGNETIC FIELD The European Geosciences Union annual meeting in Vienna saw a major data release from Swarm, ESA's trio of magnetic field satellites. Not only has the Swarm team produced the best map yet of the magnetic field in the Earth's lithosphere, it has also mapped the magnetic field coming from the oceans, tracked lightning and traced atmospheric electric currents. “This is the highest resolution model of the lithospheric magnetic field ever produced,” said Erwan Thebault (University of Nantes, France). Swarm has also produced a much bigger and better map of the rapidly changing field at the Earth's core surface. Ocean water is salty and so a conductor; Swarm picked up the tiny magnetic signal as it moves. “We can integrate the motion of all the water in the oceans, not just the tides,” said Nils Olsen (Technical University of Denmark). “This is new.” View largeDownload slide Details of Earth's lithospheric magnetic field. (ESA/Planetary Visions) View largeDownload slide Details of Earth's lithospheric magnetic field. (ESA/Planetary Visions) The data also stretched off Earth, to the polar cap, mapped in 3D. The Swarm team found that the vertical electrical current links to horizontal flow in the ionosphere. Swarm also tracked space weather, watching the evolution of geomagnetic storms, and the coupling between the weather on the ground and space weather, through lightning. https://bit.ly/2ES7HFZ © 2018 Royal Astronomical Society

Sachs, Ben

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty151

What happens when an astro-biologist, a theologian, a political theorist and a philosopher discuss the ethics of human–alien encounters? Ben Sachs reports. 1 View largeDownload slide From left to right: Ben Sachs, Sarah Rugheimer, David Wilkinson, Alasdair Cochrane, Mark Coeckelbergh. (Ash Watkins) 1 View largeDownload slide From left to right: Ben Sachs, Sarah Rugheimer, David Wilkinson, Alasdair Cochrane, Mark Coeckelbergh. (Ash Watkins) The 2018 Edinburgh International Science Festival featured an event called “Get Your Hands Off Me You Damned Dirty Alien!” While the title was a bit of a joke – alluding to the sci-fi classic The Planet of the Apes – the topic was not. I put together this panel to learn about the ethics of human–alien encounters from an astrobiologist, a theologian, a political theorist, a philosopher and an audience of the scientifically curious. It did not disappoint. The premise of the session was that we could be on the cusp of a revolution in thought to rival the Copernican revolution. Copernicus forced humanity to grapple with the theological implications of the fact that we are not at the centre of the physical universe; the discovery of intelligent life off Earth would force us to face not being at the centre of the ethical universe. In other words, what happens when we discover that humanity does not sit at the top of the ethical hierarchy? This would surely shake us out of our complacent, centuries-long tendency, in the west at least, to develop our ethical concepts and theories against a backdrop of presumed ethical, and technological, intellectual and cultural, superiority. But what new ethical model would take its place? What new ethical model should take its place? What would we owe to the aliens, and what would they owe to us? The intelligibility of this premise rests on two assumptions. First, there has to be intelligent life on other planets. Fortunately, there is a broad consensus among scientists in this field that this is indeed likely. I began the event by screening a video montage, edited by Ella Edgington, of scientists explaining why it would be surprising if there were no intelligent life outside Earth, including Neil DeGrasse Tyson telling Larry King that “it would be inexcusably egocentric to suggest that we were alone in the universe”. The montage also featured iconic movies and TV programmes presenting models – funny, inspiring, terrifying – of how those future human–alien encounters will go. Secondly, we have to assume that we might discover the existence of such life – or it might discover us. This is where the first panelist, astrobiologist Sarah Rugheimer (University of St Andrews) came in. She played the essential role of distilling how astrobiologists go about determining which exoplanets (planets orbiting stars other than our Sun) could host life. She explained, for instance, the idea that we are looking for a rocky planet in the Goldilocks zone relative to its star – not too close, not too far away. In addition, she explained how we detect heat signatures from a distant planet, which reveal key information about which chemicals are abundant in the planet's atmosphere and, by extension, whether the organic chemical reactions that are life's calling card are taking place on its surface. Rugheimer also injected a dose of reality, clarifying that we are much likelier, at least in the short-run, to detect microbial as opposed to intelligent life. Rugheimer was followed on stage by theologian David Wilkinson (Durham University) who, conveniently, also has a PhD in theoretical astrophysics. Although western religions, especially Christianity, are well known for periodically repressing scientific inquiry and undermining the public's access to the scientific facts (e.g. the prosecution of Galileo), Wilkinson reminded the audience that that is only half of the story. There is also the strand of Christianity that teaches that the way to understand God is to understand Nature, and on that basis enthusiastically champions scientific research. The question of whether there is life on other planets is of immense interest to Christian theologians, Wilkinson explained, as it would open up questions about the centrality of humanity to God's plan and whether the religious path to salvation could be the only one. Next up was Alasdair Cochrane (Sheffield University), a political theorist who began with the proposition that human–alien encounters are already happening. Non-human animals, he claimed, are aliens in our midst, with minds almost as unknowable to us as would be the minds of intelligent beings from other planets. This led into a discussion about what we can learn about potential human–alien interactions from how we humans interact with sentient animals – and what we can learn about our treatment of sentient animals from how we would want aliens to treat us. Cochrane proposed that if we want to be dealt with justly by a race of technologically and intellectually superior aliens, we had better begin reconfiguring our relations with sentient animals. We would do well to cease dealing with them on the basis of power – treating them in whatever manner our superior intellect and technology will allow us to get away with – and begin instead treating them as beings with a stake in their own lives, which they surely are. Finally, philosopher Mark Coeckelbergh (University of Vienna and DeMontfort University) spoke about the problem of incorporating aliens into our ethical thinking. Broadly speaking, he explained, we can take a more objective or more subjective approach, each of which presents its own perils. The objective approach is more common. Applied to aliens, it would involve identifying their relevant properties, such as consciousness, and reasoning about the implications of those properties for their ethical agency (what do they owe us?) and ethical patienthood (what do we owe them?). The problem with this is that we would need to know more about aliens than we might be able to learn, and it requires keeping a sterile intellectual distance from them. The subjective approach involves taking seriously the experience of imagining, perceiving and engaging with aliens, then thinking about the ethical contours such a relationship would establish. But this approach threatens to render the aliens too familiar to us, such that we lose sight of their alien-ness. Coeckelbergh proposed an ethical methodology combining the best of both. After the individual talks, the panelists took part in the question-and-answer session. At first I acted as moderator, peppering the panelists with questions of my own devising and indicating which panelist(s) I wanted to answer which question(s). I then gave the floor to the audience. Ask the audience The audience was given the following background information and asked to answer the question below before and after the discussion. Background: The first sentence of the Universal Declaration of Human Rights proclaims the “inherent dignity and equal and inalienable rights of all members of the human family”. In other words, it proclaims that all humans have dignity and rights that they cannot lose. Question: Could the existence of a superior form of life elsewhere in the universe make this proclamation untrue? choice of answers before after yes 16% 29% no 72% 68% I'm unsure 12% 3% choice of answers before after yes 16% 29% no 72% 68% I'm unsure 12% 3% What did we learn? Now the important question: What did we learn from the event? Although each of the panelists is a scholar and an independent thinker, certain themes developed during the question-and-answer period. First, and most importantly to my mind, there was a conviction that these ethical questions should be taken seriously. There was no hint of scepticism and no suggestion that our ethical concepts are irrelevant to extraterrestrial affairs. Rather, the collective presumption seemed to be that these questions have answers, though those answers will be hard to find. Of course, it is possible that the panelists were simply being courteous, but I am inclined to take at face value their willingness to engage, not to mention their willingness to travel, for this panel discussion. Second, there was broad agreement that we cannot make progress thinking through the ethical contours of possible human–alien encounters until we begin to reflect more critically on the idea of superiority. On the one hand, we have to acknowledge that superiority is always relevant to a dimension – some feature, function or activity. As humans, we are susceptible to chauvinism in choosing which dimensions to emphasize. On the other hand, we need to think clearly about the ethical relevance of superiority, where it exists, not least because the most plausible scenario for an encounter between humans and intelligent alien life involves the alien life form being superior in a variety of ways to humans. Third, and finally, there was a sense that we should push back against the predominantly gloomy tenor of most speculation about future human–alien encounters. Literature, film and television shower us with apocalyptic visions of alien attacks, which surely reflects collective anxiety about our tenuous position at the top of Nature's hierarchy. What is less emphasized is the potential upside to discovering intelligent alien life – it might be our deliverance! Maybe the aliens will give us a pain-free shortcut to solving our global warming problem. Perhaps they will even show us how to achieve peace and harmony. And there is the less quantifiable, but no less important, benefit of satisfying our cosmological curiosity. The majority opinion on the panel seemed to be that we should continue to search for alien life. And what did the audience make of all this? At the start of the event, and again at the end, we polled the audience using the Edivote system, kindly provided by the festival organizers. We gave our audience information about the United Nations Universal Declaration of Human Rights and asked how they thought the discovery of superior alien life would change it. The responses before and after the debate are shown in the box, “Ask the audience”. One lesson is that most members of this audience believe that the possible existence of a superior alien race poses no threat to human rights and dignity. But the more interesting lesson, for me, is in the difference between the first and second polls: people's ethical beliefs – even about bedrock ethical principles – are not fixed and can be influenced by dialogue. It also suggests that the revolution in ethical thinking might indeed be in the offing, as the overwhelming movement between the first and second polls was in the direction of increasing scepticism about the fixed place of humanity in the moral universe. This is an exciting result. It indicates that just as we are surely headed for scientifically interesting times as astrobiological research gathers pace, we are also headed for philosophically interesting times. There are more questions than answers – this, if anything, is an undeniable take-home message of the event. The good news is that, if this experience is any indication, there is a strong appetite among the public to engage with these questions. We had about 70 people in attendance and they seemed energized by the experience of spending 90 minutes thinking and learning about the topics addressed. Of course, I was lucky. The Edinburgh Science Festival presented the perfect opportunity to attract an audience of interested people, and I was able to assemble precisely the panel that I wanted. Be this as it may, I encourage readers to find ways to bring people together to think collaboratively about these issues. I certainly intend to continue to do so. ACKNOWLEDGMENTS I gratefully acknowledge the financial support of the Royal Society of Edinburgh (RSE). The event discussed here was funded under an RSE grant, provided to Katherine Hawley as primary investigator and me as co-investigator, that will make possible several additional events over the next 10 months on the theme of planetary exploration and ethics. For information on those events, or to comment on this article, please contact me at bas7@st-andrews.ac.uk. © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty153

This content is only available as a PDF. © 2018 Royal Astronomical Society

Edmunds, Michael

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty142

This well-connected businessman, Turner's stockbroker, was a diligent collector of art, fossils, minerals and curios, writes Mike Edmunds, and possibly served as Treasurer of the Astronomical Society. Charles Stokes (1784–1853) was a successful stockbroker. There is evidence that he travelled to Paris in 1815 with fellow RAS founder, also a stockbroker, Francis Baily (Edmunds 2017). His clients included Charles Darwin – who regarded him as a businessman of repute and a friend – and the artist J W M Turner. Stokes was an art collector and acquired a considerable number of Turner's works; he was probably the last person Turner wrote to (on his financial matters, which Stokes seems to have overseen) just before the artist's death in 1851. Turner may also have benefited from Stokes's scientific interests, which were mainly in geology, mineralogy and fossils. Stokes was an early member of the Geological Society (founded 1809) and saw service on its council, including as secretary and vice-president. Although he obviously must have had an interest in astronomy, there is little indication of active involvement. Petrified wood was a speciality, as were trilobites and zoophytes. He was involved in publications on such subjects as lead ores in Derbyshire, Mediterranean limestones with corals, and the delightfully entitled “Some fossilised vegetables of the Tilgate forest in Sussex”. He was elected to the Royal Society in 1821. An echinoderm (a marine animal related to sea urchins) was named after him: Hemicidaris stokesii. 1 View largeDownload slide Charles Stokes, 1821 etching by Mary Dawson Turner, after Sir Francis Leggatt Chantrey. (National Portrait Gallery, London) 1 View largeDownload slide Charles Stokes, 1821 etching by Mary Dawson Turner, after Sir Francis Leggatt Chantrey. (National Portrait Gallery, London) Correspondents He had a wide range of correspondents, including the great and the good of the geological world, often buying specimens himself and then making them available for study. His obituary records that no expedition started for foreign parts but that “he was in at the commencement to advise and direct the natural history arrangements”. In 1826, the explorer Captain John Franklin named Stokes Point in the Yukon after him – it is near Herschel Island. Of Stokes's origins we seem to know nothing until he appears as a member of the Geological Society in 1811. For at least the last 30 years of his life he resided in Gray's Inn, London. Verulam Buildings, a mixture of residential dwellings and professional chambers, had been erected in 1803–11. It still exists, and Stokes lived at number four. Charles Dickens wrote in 1860 of “the scowling iron-barred prison-like passage into Verulam Buildings”, but it was probably a prestigious address in Stokes's time. Of his family life, again nothing much is known. The following description by a visitor in 1845 hints at a bachelor existence: “His rooms exhibit a most picturesque confusion of learned wealth, literary, scientific and artistical – books, portfolios, fossils, dried plants, stuffed birds, animals preserved in spirits, pictures, busts, casts, coins, grotesque figures from India or Japan, snuff-boxes, and nearly everything that can be conceived.” Music and antiquarian studies were also interests, and he was a member of the Royal Asiatic Society. He was not above enjoying “high jinx” at dining clubs, or of betting bottles of champagne with his Geological Society colleague Mr Taylor on how many years toads would survive when isolated in rock cavities. He was an initial trustee of the Astronomical Society, and RAS officers' lists for the decade after 1820 suggest that he may have acted as a temporary Treasurer. He remained a Fellow until his death at the end of December 1853, having reached his 70th year. It was not a happy end. In a letter, Darwin records that “poor old Mr Stokes has lately had a very suffering ending to his life”. His friends missed his “pleasant and wise presence”. THE RAS BICENTENARY In 2020, the RAS celebrates 200 years since its founding as “the Astronomical Society of London”. It began at a meeting on 20 January 1820, with 14 men aged 24 to 65. Who were they? What was their astronomical world like? Why start a society then? This series of short articles running up to 2020 aims to sketch both the men and their times. FURTHER READING Burn C R 2013 Arctic 66 4 : 459 . A brief account of John Franklin's naming of topographical features after worthies including Stokes, Charles Babbage and the three Herschels – William, John and Caroline CrossRef Search ADS Edmunds M 2017 Astron. & Geophys. 58 1.11 CrossRef Search ADS Obituary 1854 Quarterly Journal of the Geological Society of London 10 xxvi Woodward H B 1908 The History of the Geological Society of London ( Longmans , London ). A useful volume which contains much of the sparse information on Stokes © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty133

View largeDownload slide (Left) A tightly wound-up magnetic field used as initial state in the simulation. (Right) The magnetic field structure after it has become unstable leading to the formation of knots and magnetic spots. View largeDownload slide (Left) A tightly wound-up magnetic field used as initial state in the simulation. (Right) The magnetic field structure after it has become unstable leading to the formation of knots and magnetic spots. NEUTRON STARS Magnetic hotspots on neutron stars that persist for millions of years can arise from “knots” in magnetic field lines that develop early in the lifetime of the stars. Simulations indicate that the spots – which could be just a few km across – can have field strengths of more than 10 billion Tesla. Konstantinos Gourgouliatos (Durham University) and Rainer Hollerbach (University of Leeds) used numerical simulations on the ARC supercomputer at Leeds to model the evolution of the field. They found that the 3D nature of the neutron star's overall magnetic field mattered. If most of the energy was in the dipole component of the field initially, the star ended up with a relatively simple symmetrical field. But if the toroidal field carried more than half the energy, variable spin speeds within the star would wind up and entangle the magnetic field, making it unstable. The knots that resulted emerge from the star's surface, forming spots of intensely strong magnetic field, sometimes 200 times stronger than the poloidal field. The simulations shed light on some unusual pulsar behaviour, notably in magnetars that have dipole magnetic fields that are too weak to produce their observed radio outbursts. The research is published in The Astrophysical Journal. http://arxiv.org/pdf/1710.01338.pdf © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty137

EXOPLANETS Many of the exoplanets discovered in the habitable zone of their star orbit red dwarfs, small cool stars with habitable zones at much smaller radii than our Sun. This could be a problem for their habitability, according to a study led by Eike Guenther (Thüringian Observatory, Germany), because red dwarfs can produce X-ray emissions and coronal mass ejections (CMEs). Guenther and collaborators are monitoring low-mass stars such as AD Leo, which has a giant planet in an orbit of radius of 0.02 au. In February 2018, they observed a giant flare from the star; initial results suggest the giant planet was unaffected, and that unlike similar events on the Sun, the radiation flare was not accompanied by a CME. “With sporadic outbursts of hard X-rays,” said Guenther, “our work suggests planets around the commonest low-mass stars are not great places for life.” https://bit.ly/2rfECKL © 2018 Royal Astronomical Society

Sutherland, Paul

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty148

Paul Sutherland explains how the Society for Popular Astronomy has helped students to hone their outreach skills – and you could benefit too. If you are an astronomy student wishing to develop skills in communicating science to the public, then getting involved with the Society for Popular Astronomy could help. The legendary broadcaster Sir Patrick Moore was one of the founders of this national organization when it was set up 65 years ago to help beginners to learn about astronomy and the night sky. The society produces a magazine, podcasts and videos of meetings and events as part of its role to promote space science to the general public. There are many ways in which you could help to produce these, honing some technical or creative skills that will boost your CV as well as helping a worthy cause. The SPA has published a journal, originally called Hermes, since its beginning as the Junior Astronomical Society in 1953. Renamed Popular Astronomy in 1981, the magazine is a friendly, accessible publication that blends topics to help beginners observe for themselves with updates on developments in astronomical research and space science. View largeDownload slide View largeDownload slide The SPA aims to help beginners of all ages, but one section of the magazine is squarely aimed at the “Young Stargazers” – children and members in their early teens, some of whom might become interested enough to pursue their own careers in astronomy. If you think you could contribute simply written but informative articles about particular areas of astronomy, the SPA would be delighted to hear from you. Meetings and podcasts Another way to polish up your popular science skills could be to present your work at some of the SPA's meetings, bearing in mind that you would be presenting to a lay audience that is interested but has limited scientific knowledge. There are regular meetings in London, plus occasional events at Jodrell Bank, Cambridge and elsewhere. The SPA's relaunched podcasts – first issued in 1966, on magnetic tape – could be another vehicle to help tell the world about your fascinating field. Or perhaps you are adept at using social media? If so, the SPA could help you polish your tweets. Careers Over the years, several people who started out by helping the society have gone on to successful careers in various fields of communication. Ian Ridpath was an early editor of the journal who is now a well known broadcaster and author of numerous books from popular guides to dictionaries and encyclopaedias. Robin Scagell, the current president, benefited from his hard work with the society newsletter and magazine by gaining an editing role with a major publisher of magazine partworks, and has subsequently written many authoritative guides to amateur astronomy, telescopes and binoculars. Paul Sutherland was already a news journalist but, after lengthy spells editing the society publications, he carved out a niche as a space reporter for newspapers and magazines and runs his own website, https://Skymania.com. In more recent times, some scientists have gone on to fabulous jobs communicating space science after achieving their PhDs. Emily Baldwin is now a space science editor at the European Space Agency (figure 1), having been website editor and deputy editor at Astronomy Now magazine. One of her first forays into science communication was with the SPA, where she contributed to the youth section, then called Prime Space. This later evolved into Young Stargazers; she was Chief Stargazer for several years. 1 View largeDownload slide Emily Baldwin (seated left) at work at ESA in January 2014 when the first signal was acquired from Rosetta before its encounter with comet 67P Churyumov–Gerasimenko. (ESA/J Mai) 1 View largeDownload slide Emily Baldwin (seated left) at work at ESA in January 2014 when the first signal was acquired from Rosetta before its encounter with comet 67P Churyumov–Gerasimenko. (ESA/J Mai) 2 View largeDownload slide Attendees at the SPA's Cambridge Convention in 2017 observed Mercury in daylight using the historic Northumberland Telescope. (P Sutherland) 2 View largeDownload slide Attendees at the SPA's Cambridge Convention in 2017 observed Mercury in daylight using the historic Northumberland Telescope. (P Sutherland) Emily says: “Writing for the SPA and other societies while I completed my PhD, and receiving guidance from the editors of the time, was a valuable experience that allowed me to widen my range of writing skills, paving the way for the dream jobs I would have later.” Elizabeth Pearson joined one of the UK's major astronomy magazines following her stint with the SPA. She says: “I took over as Chief Stargazer after Emily, along with a colleague of mine, George Ford, also while doing my PhD. I now work as news editor for BBC Sky at Night Magazine. In the last five years I have done nearly 100 interviews on national and regional radio talking on all matters space, as well as a handful of TV interviews (including one on my knees in the middle of a rattlesnake-infested field in Nebraska … that was interesting) and even a Channel 4 documentary on the Chel-yabinsk meteor. “With my work for SPA, I not only honed my writing but learned loads of other skills along the way – from how to work with another writer to create the best copy, to wrangling unruly contributors. I don't think I would be where I am today if I hadn't had the SPA to help me take those first steps.” Science writer Amanda Doyle was recently editor of Popular Astronomy and is now a staff reporter for The Chemical Engineer, the magazine for the Institution of Chemical Engineers. Amanda wrote freelance astronomy articles throughout her PhD and postdoc; this, combined with her experience as assistant editor and then editor of Popular Astronomy, helped her to move into a full-time science-writing job. Stephen Serjeant of the Open University is the current vice-president of the SPA and will take over as president next year. “It's always a pleasure to see a new copy of Popular Astronomy. There have been so many talented voices in public engagement that have honed their craft in this magazine,” he says. “I think it plays an important role as a springboard for people with a flair for science communication. Picking up the magazine, I often wonder if I might be seeing the astronomy outreach equivalent of The Beatles at the Cavern Club.” If you can help in any way, please email the current president Robin Scagell (president@popastro.com). And don't forget that the SPA is also seeking another kind of support: the professional community can help the SPA to promote astronomy to the public simply by joining. Membership in the UK costs £22 a year, with discounts for those who pay by direct debit. To find out more, visit the SPA's website at https://www.popastro.com. © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty132

EXOCHEMISTRY Olivia Venot (Laboratoire Interuniversitaire des Systèmes Atmosphérique in Paris) and Eric Hébrard (University of Exeter) have turned to chemical models designed for car engines to track chemical pathways in hot Jupiters and warm Neptunes. “Chemical networks developed for car engines are very robust as a result of years of intense R&D, lab studies and validation,” said Venot. “Car models are valid for temperatures up to over 2000 °C and a wide range of pressures, so are relevant to the study of a large diversity of warm and hot exoplanet atmospheres.” http://bit.ly/2rcFzEm © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty139

EARLY UNIVERSE A team led by David Sobral (University of Lancaster) has mapped galaxies in the early universe, between 11 and 13 billion years ago. The team used data from the Subaru Telescope in Hawaii and the Isaac Newton Telescope in the Canary Islands and found almost 4000 early galaxies, mostly small, typically one-thirtieth of the size of the Milky Way. “These early galaxies seem to have gone through many more ‘bursts’ when they formed stars, instead of forming them at a relatively steady rate like our own galaxy,” said Sobral. “Additionally, they seem to have a population of young stars that is hotter, bluer and more metal-poor than those we see today.” The team published its data in two papers in Monthly Notices of the Royal Astronomical Society. https://bit.ly/2HH2Sk7 https://bit.ly/2HJDZUP © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty106

COMPUTING Machine learning is becoming a useful tool for astronomical data selection, as two projects show. “Deep learning”, developed for such applications as facial recognition, has been used for galaxy classification. An international team trained its software on simulations of three stages of galaxy evolution, as they would appear if observed by the Hubble Space Telescope. It tested the process on actual HST images and found success. The work is published in The Astrophysical Journal by Huertas-Company et al. A different approach has helped to refine estimates of which exoplanets in binary star systems have a chance of being not just habitable, but survivable. Such planets need a stable orbit for life to have any chance, but the standard approach to calculating the stability of orbits has not proved useful. Instead, Chris Lam (Columbia University, USA) and colleagues used a large training set of stable orbits for binary systems, and their network was able to out-perform the accuracy of the standard approach after just a few hours. GALAXIEShttp://bit.ly/2waEdiG EXOPLANETShttp://bit.ly/2JLquk6 © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty113

STAR PROPERTIES The first detection of gravitational waves from a neutron star merger has set some limits on the extreme matter of neutron stars. The gravitational wave data limit the tidal deformabilities of the stars involved, in turn limiting the families of equations of state for neutron star matter. Specifically, the data rule out large neuton stars, putting the radius of a 1.4-solar-mass neutron star at up to 13.6 km only. Annala et al. and Fattoyev et al. published independent studies in Physical Review Letters. http://journals.aps.org/prl © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty111

NIFS A longstanding question about the ice giant Uranus has been resolved with the Gemini North telescope on Maunakea, Hawaii. Patrick Irwin (University of Oxford) led an international team using Gemini's Near-Infrared Integral Field Spectrometer (NIFS) to sample the region above the main visible cloud layer in Uranus's atmosphere. Clouds made of hydrogen sulphide or ammonia would leave traces of these species there. “We were able to detect them unambiguously thanks to the sensitivity of NIFS on Gemini,” said Irwin. These data are valuable for understanding the origin of planets; the proportions of N and S depend on temperature and location in the Sun's dusty disc. http://www.gemini.edu/node/21050 © 2018 Royal Astronomical Society

Daniels, Paul A

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty141

Paul A Daniels reports on the rennaissance of the Federation of Astronomical Societies. View largeDownload slide View largeDownload slide The Federation of Astronomical Societies (FAS) is a society of societies, formed in the UK in 1974 with the goal of helping its members practise astronomy and collaborate on matters of common interest. Now it has a membership of 219 societies representing more than 12 000 (mostly) amateur astronomers. Almost all members are on the UK mainland with the rest in Northern Ireland, the Isle of Man, the Channel Islands, Gibraltar and Spain. The FAS encourages the teaching of astronomy, offers advice on practical problems that societies encounter and helps them find speakers for meetings. It also produces a newsletter three times year, a handbook, booklets with helpful advice and, crucially, has negotiated a group public liability insurance (PLI) policy with lower premiums – indeed, some smaller societies can hold public outreach events only because of this. The annual handbook is a valuable resource with listings of local societies, equipment suppliers, speakers and places to visit, as well as articles on topics such as buying a second-hand telescope, fundraising and drafting a constitution. Each autumn, the FAS holds a convention combined with its AGM. This has been held at the Institute of Astronomy, Cambridge and, for the past four years, at the University of Birmingham. The convention offers eminent astronomy speakers, displays and exhibitors. The society plans to increase delegate numbers by opening the day to the public (apart from the AGM). Problems – and a solution Unfortunately, the society ran into difficulties last year, in particular when several long-standing members of the Council chose to stand down, feeling with good reason that they had “done their bit”. It was difficult to find candidates for election to Council, suggesting that the relevance of the FAS to members was declining – and raised the question of whether the FAS had a future. The Council appealed to the members, warning that the FAS may cease to exist without enough candidates for election at the AGM. The troops rallied and the FAS started 2018 with a full complement on Council – but also with a desire to change the society and make membership mean something. An FAS Council brainstorming meeting in October generated several possible changes to address the burdens of bureaucracy that astronomy societies face. Some of the changes are to the FAS itself and others to its relationship with members and the services offered. A great frustration for volunteers managing astronomical societies is the need to keep up with legislation and best practice, especially in a wider society where people have become more litigious and more prone to take offence – not to mention the magnifying effect of social media. In the event of a problem, it is often those on the managing committee of a society who are exposed directly to the risk and financial implications of any legal challenge. The FAS has proposed changes to focus on helping societies with this administrative burden by supplying the necessary advice on legislation in a plain English form, tailored to amateur astronomical societies, for example by offering templates for best practice. Organizers will be freed to do more astronomy and develop their societies and what they offer to their members. This is what the FAS hopes to provide: advice on the pros and cons of becoming a charity or other legal entity advice on tax and the relationship with HMRC advice on (and options for) creating an effective constitution guidance on a code of conduct and ways to promote diversity health and safety advice, including on the use of laser pointers and the protection of vulnerable children and adults advice on data protection regulations advice on fundraising templates for assessment of risk for outreach events. The broad goal of these changes is to help member societies work in a safe and legal manner. The FAS Council has discussed whether adopting some of these templates should be a mandatory condition of membership or whether there should be a two-tier membership: Premium for those that adopt them and Standard for those that don't. About 10% of our members responded to a request for comments and there has been fairly broad agreement, but with variable support for making some of the proposals mandatory. Members of the FAS Council are now busy researching and writing the advice documents. The society hopes to decide on the details of implementation after more consultation with members. Again, this comes back to the issue of how to make membership of the FAS mean something – we could become a standards body for the amateur astronomical community. But, above all, this promising new role for the Federation offers a meaningful way to support its member societies – with less time ticking boxes and more time seeing stars. MORE INFORMATION http://fedastro.org.uk © 2018 Royal Astronomical Society

Serjeant, Stephen

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty140

View largeDownload slide View largeDownload slide Stephen Serjeant applauds the creativity on show at the premiere of The Planets 360, one of the RAS 200 anniversary outreach projects. Have you been to a planetarium in the last 10 years? If not, then stop reading, put down A&G and arrange a trip. Trust me. Do it now. It is glorious. At the planetarium at the National Space Centre in Leicester you feel genuinely immersed in the action – and it beats any cinema hands down. I was delighted to be invited to the National Space Centre to the premiere of ThePlanets 360, a new planetarium show made by NSC Creative and funded by the RAS 200 Sky & Earth anniversary project. The production team has avoided the well-trodden route of making a didactic educational experience, instead concentrating on triggering emotional reactions with engaging visuals. The first half uses captivating and intriguing recent planetary images accompanied by Holst's The Planets orchestral suite. The second is a radical – possibly controversial – reimagining of a planetarium show with modern electronic music and more impressionistic visuals. This is genuinely different, and I hope it finds new audiences. 1 View largeDownload slide An astronaut spirals into Jupiter's Red Spot. (NSC Creative) 1 View largeDownload slide An astronaut spirals into Jupiter's Red Spot. (NSC Creative) The classical section, performed by the Philharmonic Orchestra, opens with Mars with its dramatic 5/4 time signature. The topography of the Red Planet is beautifully rendered and there is a lovely engineering layout of a Mars mission and its launch. The rocket does not launch in the serene, slow-motion way shown in movies, but more like a missile – and the link with warfare is no accident. In science we try to do great things for human understanding, but the wider activity that makes it possible can be part of darker human motivations. The sections on Venus and Mercury showcase geological mapping of their surfaces, but my favourites were the gas and ice giants. There's a certain incongruity between Holst's rendering of these planets and the mysteries we are uncovering about their clouds and poles, as well as the diversity of their moons. Holst might have written differently if he had seen Jupiter's filigree detail. The rendering of Saturn is particularly impressive, with the rings passing overhead and Saturn looming closer directly behind you, as you fall backwards into the planet. Creative freedom In the second half of the show, the production team allowed themselves much more creative freedom and the result is very different. The music is “ambient trance” and, as a classical musician remarked to me afterwards, the show would work well in a dome at Glastonbury Festival. Again, it opens dramatically with Mars, this time with an explicit theme of war. Images of spacesuits are interspersed with skulls and crumbling bodies, using bright lights against the devastation of the barren martian desert. These dark human instincts find some antidote in Jupiter, in which a person in a spacesuit falls into the Red Spot, through fluid dynamical swirls and ultimately, 2001-style, into a hidden civilization, reminding us that humans are capable of greater things than war. If you care about the physics of whether this is possible, you are right, but you're also missing the point. Venus had the most positive reactions from astronomers afterwards. Geometric tessellations are everywhere, partly surrounding Venus (a nod to its powerful greenhouse atmosphere?) and in small clumps emitted from the surface, reminding me of how I imagine small, volatile molecules. The landscape rendering is simplified, using geometric blocks like an old video game, reminding me of how physicists make mental approximations. The production team also had an imaginative take on Mercury, portraying its eventual destruction by the Sun. The ice giants are impressionistic. Uranus, Holst's “magician”, with its mysterious banded cloud structure, is articulated as mysterious poised human characters made with horizontal striations. Neptune “the mystic” is quite cryptic, with a trio of swimming machines or creatures. The piece ends emotively with Saturn, “bringer of old age”, which imagines life on one of the moons. Old life sends out spores to create the new, and the circular imagery reminds me of both Saturn's rings and of the circle of life. The electronica section is bound to be controversial among academics, but all creative fields need to take risks, and I maintain that these are risks worth taking and that these pieces succeed. We humans are not simply rational beings, and science needs to engage on more than just an intellectual level. © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty102

View largeDownload slide View largeDownload slide OUTREACH The European Southern Observatory has opened a new centre for the public to find out about its activities and the wonders of the universe. Supernova is a science centre and planetarium, based at ESO Headquarters in Garching, Germany. Its architecture is inspired by a binary star system and the décor, such as the striking ceiling shown above, reflects the southern skies. (ESO/P Horálek) http://eso.org/public/news/eso1813 © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty101

View largeDownload slide View largeDownload slide SKA The SKA Pathfinder telescope MeerKAT (one antenna shown above) has produced its first science paper, albeit with only a fraction of its full 64 antenna array. The first published MeerKAT data combined with X-ray data from a range of observatories to explore an unusual variable magnetar. Being built in the Northern Cape province of South Africa, MeerKAT continued an observing sequence begun at the Parkes 64 m radio telescope. The new data were collected using 14 of the 16 available antennas. The target was one of only four magnetars to have displayed radio emission, PSR J1622-4950. It stopped emitting X-rays in 2010 and radio emission stopped in 2014, but in late 2016 it became active. The data, published in The Astrophysical Journal by Camilo et al., suggest that the new radio emission comes from a different place on the star. http://bit.ly/2reYGgi © 2018 Royal Astronomical Society

Cruise, Mike

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty152

The new RAS President discusses painting, gravitational waves and losing his voice. View largeDownload slide View largeDownload slide What do you hope to achieve as RAS President? The President must support the RAS staff in maintaining the Society and its activities, but just as important is to prepare the RAS for change – to meet new challenges and to be more relevant for its members. As Brexit takes hold it is not easy to foresee all the complications that may result from our withdrawal from the EU. The RAS must be active in the public debates about funding, especially for astronomy and geophysics which sometimes have links to economic growth that are complex and long term. When and why did you join the RAS? As a student at school I was fortunate to go to several lectures at the Royal Institution and so I had a vague idea what learned societies provided for their members and for the public. I joined the RAS in 1974 and was able to benefit from the RAS Ordinary Meetings, especially from talks on subjects outside my own. What drew you to astronomy? Like many growing up after the second world war, I was fascinated by radio technology. The excitement of soldering a handful of components together and then hearing radio stations from across the globe is difficult to explain to generations used to easy internet access. But it was a magical experience. One day I found a book, Radio Astronomy for Amateurs, which led to an interest in astronomy and physics. How did you come to work on gravitational waves? After obtaining my PhD in X-ray Astronomy, I was asked to contribute to the HIPPARCOS mission that ESA was starting. I realized that the angular precision of the stellar position measurements from HIPPARCOS would be comparable to the accuracy of the tests of the bending of light by the gravitational field of the Sun. To understand this possibility better, I needed to study general relativity. I set myself a problem which I believed had not been solved in the literature: to calculate the effect of a passing gravitational wave on the polarization of an electromagnetic wave – and my interest in gravitational waves and the problem of detecting them was launched. What does the discovery of gravitational waves mean? It is a remarkable turning point in astronomy. Up until September 2015, more or less everything we knew about the universe was derived from electromagnetic observations. Since the last quarter of the 20th century, though, many of the problems in understanding the universe have been to do with its gravitational content, not its heat content. So opening the gravitational sector for observations is vital. Who has been the biggest influence on your career? I have worked under some impressive scientific leaders and with high-quality engineers. But without my father's example I would not have chosen the career I have had. He grew up poor and had little education beyond school, and yet he developed an interest in leather and mammalian skin which led to more than 30 refereed publications. There was always a microscope on our dining table and for years I supposed every family had one. His perseverance, energy and interest in everything around him shaped my view of the world. What is your greatest achievement so far? In 1995, I moved to the University of Birmingham and was given the opportunity to set up research activities in a subject area of my choice. I chose to start a gravitational wave group and hired some excellent scientists who now lead it. I was very proud when the Birmingham Group played a significant role in the discovery of gravitational waves. What is your biggest mistake? In the early 1980s, I was asked to give a public talk but developed a sore throat the day before. Rather than let the organizers down, I struggled through, my voice becoming weaker and weaker. That was a mistake for the organizers and a bigger mistake for me: I couldn't speak for two years and needed three operations and intensive speech therapy to recover. What do you do for fun? I paint portraits. The human face is incredibly important in terms of culture, communication and our evolution. I find it fantastically challenging and, in the 5 to 10 hours needed to complete a portrait, my mind is completely engaged on a different set of issues from my normal duties. It is amazingly therapeutic. © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty138

EXOBIOLOGY A potential problem for the emergence of life on other planets may lie in the supply of phosphorus – one of the CHNOPS elements essential for life on Earth. Jane Greaves and Phil Cigan (University of Cardiff) have been looking for phosphorus, P, using the William Herschel Telescope on La Palma in the Canary Islands, comparing abundances of phosphorus and iron in infrared spectra in order to compare their abundances in supernova remnants. So far the Cardiff team has data from two supernova remnants: Cassiopeia A and the Crab Nebula. The Crab data so far show much less P than Cas A, although difficult observing conditions limited the data that they have been able to collect on the nebula; they plan to go back and check. The nature of the supernova and its precursor star may affect the elements produced and ejected in the explosion; Cas A resulted from the explosion of a rare super-massive star. http://bit.ly/2rd4mbA © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty134

View largeDownload slide View largeDownload slide OUTREACH Everybody knows the links between The Beatles and Liverpool – but what about their links with astronomy? Viviana Ambrosi knows all about them and spoke at the meeting about using the connections for outreach. Her book, La Scienza dei Beatles, documents both astronomical discoveries inspired by the band and research that their success funded. There are asteroids named after the group, a diamond star called Lucy – what else – and NASA's Lucy mission. The lads from Liverpool also contributed to a Nobel Prize: their record company, EMI, used the profits from their White Album to fund research, including Godfrey Hounsfield's work on X-rays, which led to the invention of the CT scanner. http://bit.ly/2FvRHVA © 2018 Royal Astronomical Society

2018 Astronomy & Geophysics

doi: 10.1093/astrogeo/aty126

View largeDownload slide View largeDownload slide SDO 2D images of structures on the Sun such as prominences and solar tornadoes give a misleading impression of the movement involved, according to Nicolas Labrosse (University of Glasgow) and an international team from Glasgow, Paris Observatory, the University of Toulouse and the Czech Academy of Sciences. Data from the multiwavelength Atmospheric Imaging Assembly (AIA) instrument on NASA's Solar Dynamics Observatory appear to show tall, twisting structures in the Sun's plasma, described as tornadoes based on the similarity of their appearance to tornado funnels on Earth. But Lebrosse and the team have added velocities derived using the Doppler effect and shown that the 3D pattern is different. “Despite how prominences and tornadoes appear in images, the magnetic field is not vertical, and the plasma mostly moves horizontally along magnetic field lines,” said Labrosse. “However, we see tornado-like shapes in the images because of projection effects, where the line-of-sight information is compressed onto the plane of the sky.” The picture shows an erupting solar prominence observed by SDO on 31 August 2012. (NASA/SDO/GSFC) http://bit.ly/2HGWvgI © 2018 Royal Astronomical Society