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- Title
Characteristics of Energetic Oxygen Ions Escaping From Mars: MAVEN Observations.
- Authors
Lin, R. T.; Huang, S. Y.; Yuan, Z. G.; Jiang, K.; Xu, S. B.; Wei, Y. Y.; Xiong, Q. Y.; Zhang, J.; Zhang, Z. H.; Yu, L.; McFadden, J.
- Abstract
We used nearly 4 years of data from the Mars Atmosphere and Volatile EvolutioN orbiter to map the distribution and motion of energetic O+ ions (2.3–30 keV) in the Martian environment. Our analysis reveals two typical features: a strong plume of energetic O+ ions in the +E hemisphere at dayside, driven by the convective electric field, and a less strong tailward gathering flow of energetic O+ ions in the –E hemisphere at nightside. Based on previous studies, this study reveals more details on energetic O+ ion escape: (a) velocities for energetic O+ ions between bow shock and induced magnetic boundary have much larger Y‐axis component, indicating that energetic O+ ions may not only escape along +Z‐axis but also slip away on the Y‐axis in MSE coordinates; (b) energetic O+ ions at low altitude in the –E hemisphere have little component along Y‐axis, and energetic O+ ions at nightside in the –E hemisphere "gather" along the tail and finally escape from the planet, driven by the convective electric field and the Martian current system. Comparing the fluxes and escape rates of energetic O+ at different distances away from the Sun and under different solar activities, we found that the heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level. Plain Language Summary: The answer to how does the water escape from unmagnetized planets like Mars is debated. Due to lack of an intrinsic global magnetic field, the Martian upper atmosphere can be easily eroded by the solar wind, which is an effective way for the water to escape after being ionized to H+ and O+. The motion of energetic O+ ions can be used as a probe of the escape of heavy ions. In present study, we report a global map of energetic O+ ions outflows for the first time using nearly 4 years of data from the Mars Atmosphere and Volatile EvolutioN orbiter. Our analysis reveals two typical features: a strong radial plume of energetic O+ ions in the northward dayside, driven by the convective electric field, and a less strong tailward gathering flow of energetic O+ ions in the southward nightside. In addition, we found that the heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level. These results are helpful to understand where and how the water escape from the unmagnetized planets to the space. Key Points: A global map of energetic O+ ions (from 2.3 to 30 keV) outflows is built using 4 years data from Mars Atmosphere and Volatile EvolutioNEnergetic O+ ions are able to slip away along Y‐MSE direction in the plume and "gather" along the tail in the −E hemisphereThe heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level
- Subjects
MARS Atmosphere &; Volatile Evolution (Artificial satellite); SOLAR energetic particles; ELECTRIC fields; HELIOCENTRIC model (Astronomy); MARS (Planet)
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 8, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2021JA029507