Journal of Geophysical Research: Space Physics
Oxygen Ion Energization at Mars: Comparison
of MAVEN and Mars Express Observations
to Global Hybrid Simulation
, R. Modolo
, A. Fedorov
, and M. Holmström
Finnish Meteorological Institute, Helsinki, Finland,
Department of Electronics and Nanoengineering, School of Electrical
Engineering, Aalto University, Espoo, Finland,
Laboratory for Atmospheric and Space Physics, University of Colorado
Boulder, Boulder, CO, USA,
LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC University Paris CNRS, Guyancourt, France,
Université de Toulouse, UPS-OMP, IRAP, Toulouse, France,
Swedish Institute of Space Physics, Kiruna, Sweden
We study oxygen ion energization in the Mars-solar wind interaction by comparing particle
and magnetic ﬁeld observations on the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express
missions to a global hybrid simulation. We ﬁnd that large-scale structures of the Martian-induced
magnetosphere and plasma environment as well as the Mars heavy ion plume as seen by multispacecraft
observations are reproduced by the model. Using the simulation, we estimate the dynamics of escaping
oxygen ions by analyzing their distance and time of ﬂight as a function of the gained kinetic energy along
spacecraft trajectories. In the upstream region the heavy ion energization resembles single-particle solar
wind ion pickup acceleration as expected, while within the induced magnetosphere the energization
displays other features including the heavy ion plume from the ionosphere. Oxygen ions take up to 80 s and
travel the distance of 20,000 km after their emission from the ionosphere to the induced magnetosphere
or photoionization from the neutral exosphere before they have reached energies of 10 keV in the plume
along the analyzed spacecraft orbits. Lower oxygen ion energies of 100 eV are reached faster in 10–20 s
over the distance of 100–200 km in the plume. Our ﬁnding suggests that oxygen ions are typically observed
within the ﬁrst half of their gyrophase if the spacecraft periapsis is on the hemisphere where the solar wind
convection electric ﬁeld points away from Mars.
Mars is the second smallest object in the solar system with a signiﬁcant atmosphere. The planet has likely lost
a lot, even an oceanful, of water since its childhood. As 89% of the mass of the water molecule is in oxygen,
most of the energy and momentum required to remove constituents of water from a gravity well of a celestial
body goes to oxygen. It is debated how much oxygen and other heavy elements the solar wind has eroded
from Mars during the age of the solar system.
The solar wind drives the erosion of ionized volatiles from globally unmagnetized Mars and Venus through
their atmospheres via several channels (Lundin, 2011). The largest observed structure of the ion escape from
Mars was recently termed as the heavy ion plume (Brain et al., 2010). The plume forms when the solar wind
convection electric ﬁeld accelerates heavy ions of atmospheric origin from ionospheric altitudes to several
planetary radii distances. These planetary pickup ions follow cycloid trajectories with the Larmor radii large
or comparable to the size of an induced magnetosphere in the magnetized solar wind plasma ﬂow.
The Mars-induced magnetosphere and ion escape are hemispherically asymmetric as seen in situ observa-
tions, for example, on the Mars Express (MEX) mission (Barabash et al., 2007; Fedorov et al., 2006), and on
the Mars Atmosphere and Volatile EvolutioN (MAVEN or shortly MVN) mission (Dong et al., 2015; Jakosky
et al., 2015) as well as in global simulations of the Mars-solar wind interaction (Brecht, 1990; Kallio et al., 2010;
Ledvina et al., 2017; Ma et al., 2015; Modolo et al., 2016; Najib et al., 2011). Typically, the near space around Mars
is divided in fourquadrants or hemispheres toanalyze asymmetries of the ion escape (Brain et al., 2015; Nilsson
et al., 2011). The plume is located in the hemisphere where the solar wind convection electric ﬁeld points away
from the planet, termed the
hemisphere, which dominates the ion escape rate compared to the opposite
) hemisphere. The orientation of the plume perpendicular to the Mars-Sun axis is along the solar wind
• Mars heavy ion plume is measured by
• Ion time and distance of ﬂight are
estimated based on a global model
• Oxygen ions are observed near Mars
within the ﬁrst half of their gyrophase
Jarvinen, R., Brain, D. A., Modolo, R.,
Fedorov, A., & Holmström, M.
(2018). Oxygen ion energization
at Mars: Comparison of MAVEN
and Mars express observations
to global hybrid simulation.
Journal of Geophysical Research:
Space Physics, 123, 1678–1689.
Received 13 OCT 2017
Accepted 27 JAN 2018
Accepted article online 8 FEB 2018
Published online 27 FEB 2018
©2018. American Geophysical Union.
All Rights Reserved.
JARVINEN ET AL.