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Characteristics of Energetic Oxygen Ions Escaping From Mars: MAVEN Observations

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.