Oxygen Pickup Ions Measured by MAVEN: A Link to the Extended Exosphere of Mars

Abstract:

The exosphere of Mars is very extensive and the hot oxygen corona, produced photochemically in the ionosphere, extends tens of Martian radii from the planet. This exosphere is a source of oxygen ions, picked up by the solar wind electric and magnetic fields, and accelerated toward Mars. The pickup ion energies depend on solar wind conditions and during high speed solar winds (> 500 km/s) with large angles between the solar wind bulk flow velocity and the interplanetary magnetic field (> 50 degrees), oxygen pickup ions can reach energies high enough (> 60 keV) to be detected by SEP. The SEP (Solar Energetic Particle) instrument is an energetic particle detector on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft, scheduled to reach Mars in September 2014. In this study, the instrumental geometry and response function of SEP are included in a modeling analysis of the effect that different solar wind conditions and SEP look directions will have on O+ pickup ion energy spectra. We describe a method that provides constraints on neutral oxygen escape models by linking the SEP energy spectra to the photochemical source of hot oxygen. Additionally, we present model results for pick-up ion distributions, and their possible detection by the SEP, STATIC (SupraThermal And Thermal Ion Composition) and SWIA (Solar Wind Ion Analyzer) instruments on board MAVEN, during the close passage of Comet Siding Spring to Mars on October 19, 2014. Large ion flux enhancements near Mars originating from the comet’s neutral coma are predicted.