Journal article
Mars' O+ and O2+ Ion Escape During Disappearing Solar Wind Events
Journal of geophysical research : Space physics (2013 - Present), Vol.131(8), e2025JA034801
08/2026
DOI: 10.1029/2025JA034801
Abstract
Disappearing solar wind events (DSWEs), intervals when the solar wind proton density <1 , represent one extreme of the Mars solar wind interaction. Using data from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission from February 2016 to May 2024, 154 orbits across 90 unique days were identified. During these events, the solar wind kinetic energy flux had a median value of ∼0.08 and never exceeded 0.37 , whereas normal times have a median value twice as large (∼0.16 ) and maximum values exceeding 8 . In contrast, electromagnetic energy fluxes and solar ionizing irradiance remained near normal levels. Observations of and density and fluxes from MAVEN's SupraThermal and Thermal Ion Composition (STATIC) instrument were analyzed. During DSWEs, ion density and ion flux distributions are significantly restructured, consistent with expansion of Mars' ionosphere and induced magnetosphere. Ion escape rates are significantly reduced during DSWEs compared to normal solar wind conditions, with falling to ∼75% and to ∼88% of normal values (9.45 and 1.30 ions/s). DSWE ion fluxes binned by solar wind kinetic and solar ionizing irradiance followed the same empirical relations as under normal conditions, whereas DSWE ion fluxes were depleted relative to the background trend for solar wind electromagnetic energy. Thus, the observed decrease in ion escape is likely attributable to the reduced solar wind kinetic energy flux. These results suggest that even under extreme solar wind density reductions, Mars' ion escape remains mostly governed by the same background drivers as during normal times. Mars once had a thick atmosphere, but today most of it has been lost to space. One important way this happens is through the escape of charged oxygen ions, which are carried away by the solar wind. This study looks at what happens during “disappearing solar wind events,” rare times when the solar wind becomes extremely thin. Using more than eight years of data from NASA's MAVEN spacecraft, we identified 154 MAVEN orbits across 90 days with such events between 2016 and 2024. During these times, the outer boundary of Mars' atmosphere expanded to much higher altitudes, and the pattern of escaping ions became more spatially complex and variable. The rate at which oxygen ions escaped to space appeared slightly reduced, though not dramatically so. The relationship between the motion of solar wind particles and ion escape stayed the same, while the relationship between solar wind electromagnetic energy and ion escape was weaker than under normal conditions. These events represent one extreme of how the solar wind affects Mars' atmosphere. 154 spacecraft orbits with solar wind proton density under 1 were identified at Mars between February 2016 and May 2024 During Disappearing solar wind events (DSWEs), escape is 75% and is 88% of normal values ( and ions/s) During DSWEs, reduced ion escape likely reflects less incoming solar wind kinetic energy
Details
- Title: Subtitle
- Mars' O+ and O2+ Ion Escape During Disappearing Solar Wind Events
- Creators
- N. R. Schnepf - University of Colorado BoulderY. Dong - University of Colorado BoulderH.‐W. Shen - University of Iowa, Physics and AstronomyJ. S. Halekas - University of IowaW. K. Peterson - Laboratory for Atmospheric and Space PhysicsK. G. Hanley - University of California, BerkeleyS. Shaver - University of Colorado BoulderA. Azari - University of AlbertaN. Jones - University of Colorado BoulderD. Brain - University of Colorado BoulderE. M. B. Thiemann - University of Colorado BoulderJ. R. Espley - Goddard Space Flight CenterJ. P. McFadden - University of California, Berkeley
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research : Space physics (2013 - Present), Vol.131(8), e2025JA034801
- DOI
- 10.1029/2025JA034801
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Wiley
- Grant note
- National Aeronautics and Space Administration
This work was supported by the NASA MAVEN project through the Mars Exploration Program. A. R. Azari acknowledges the University of Alberta and Canada CIFAR AI Chairs program via the Alberta Machine Intelligence. The authors also sincerely thank the anonymous reviewers for their thoughtful feedback that strengthened this work. Open access publishing facilitated by Adelaide University, as part of the Wiley - Adelaide University agreement via the Council of Australasian University Librarians.
- Language
- English
- Date published
- 08/2026
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9985219915602771
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