Cross-Shock Electrostatic Potentials at Mars Inferred From MAVEN Measurements.

A bow shock is generated by the interaction of the solar wind with the planetary global dipole field (e.g., Earth), or with (mainly) the planetary ionosphere (e.g., Mars). The cross-shock potential has been well studied at Earth but not yet for Mars. We infer and approximate the peak in the frame invariant de Hoffmann-Teller shock potential profile at Mars (ϕ) with data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. We find that ϕ and its ratio to the solar wind ram ion energy (E_ram) vary similarly against solar zenith angle (SZA, a proxy for the angle between the solar wind flow and the shock normal) and magnetic latitudes. Our results also reveal no significant dependence of the shock potential on parameters such as the angle between the upstream interplanetary magnetic field (IMF) and the shock normal and plasma beta of upstream solar wind. There is a somewhat positive correlation with the magnetosonic Mach number and the magnetic amplification ratio across the shock. We also find a solar cycle effect on the shock location, closer to the planet near the solar minimum, as expected. Lastly, similarities and differences of cross-shock potentials at Mars and Earth are discussed. Characterizing electron energization and high-altitude ion loss at Mars is influenced by the bow shock and thereby the work here. [ABSTRACT FROM AUTHOR]