Characteristics of Energetic Oxygen Ions Escaping From Mars: MAVEN Observations

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.

Acceleration of Pick‐Up Ions in the Martian Magnetosheath: A Tianwen‐1 Case Study

“…Various studies have touched upon the escape of PUIs driven by this electric field, focusing particularly on the energy variations and trajectories of low‐energy downtail O + populations and high‐energy polar O + populations (Curry et al., 2014; Lin et al., 2021). Maybe the thickness of the magnetosheath is negligible compared with the gyroradius of the PUI, it seems no special attention has been paid to the acceleration inside the magnetosheath.…”

Heavy Ion Escape From Martian Wake Enhanced by Magnetic Reconnection

“…Ion escape, in particular, through magnetotail or plasma wake, is a significant part of Martian atmospheric escape in the present time (Barabash et al., 2007; Dubinin et al., 1993). The main ion escape channels for Mars involve pickup ion plume, loss through tail plasma sheet, and loss due to pickup of exospheric oxygen upstream from the planet (Brain et al., 2015; Dong et al., 2015, 2017; Dubinin et al., 2011, 2017; Lillis et al., 2015; Lin et al., 2021). Ion escape through the tail or the wake region, however, should be inefficient because of Mars' obstruction.…”