Global Ambipolar Potentials and Electric Fields at Mars Inferred From MAVEN Observations

The motion of charged particles is governed by electromagnetic forces at high altitudes at Mars and thus the characterization of electrostatic potential and electric fields is important for understanding ion escape at Mars. In this study, we utilize measurements from the Mars Atmosphere and Volatile EvolutioN mission to derive electrostatic potentials above the collisional atmosphere at Mars. We find averaged potentials to be up to similar to 100 V in the magnetosheath and down to similar to-70 V in the tail, with respect to the upstream. We then derive electric fields based on averaged potential maps, ranging similar to 0.01-0.1 $\sim 0.01-0.1$ V/km. These data-derived electric fields are in good agreement with ambipolar electric fields from a multi-fluid magnetohydrodynamic (MHD) model. MHD results also reveal that these large electric fields mainly originate from the electron pressure gradient in the magnetosheath and in the transition region from the hot solar wind flow to the cold ionospheric flow. This work provides the first data-based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere).

Automated summary

This study utilizes data from the Mars Atmosphere and Volatile EvolutioN mission to derive electrostatic potentials and electric fields above Mars' collisional atmosphere. The results show significant variations in averaged potentials and electric fields in different regions, with good agreement between data-derived electric fields and the multi-fluid magnetohydrodynamic (MHD) model. The work provides the first data-based characterization of global ambipolar electric fields at Mars.