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One possible ion escape channel at Mars is a polar wind-like outflow driven by parallel electric fields and/or other acceleration mechanisms. With independent potential estimates from ionospheric photoelectron measurements by the Solar Wind Electron Analyzer (SWEA) and ion measurements by the SupraThermal And Thermal Ion Composition (STATIC) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, magnetic field-aligned potentials are calculated as the difference of the two. The calculated field-aligned potentials have average values that range from 0 to -1.5 V, relative to the ionospheric source region. These field-aligned potentials likely result from ambipolar electric fields and are found on both closed and open field lines. On the dayside, these potentials range from 0 to -0.7 V, corresponding to an electric field magnitude < 3 mV/km, which peaks near the ion exobase and can effectively accelerate ions and enhance ion outflow.

Plain Language Summary The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission is dedicated to studying atmospheric loss from Mars at the current epoch and estimating the total loss to space over Martian history. Atmospheric escape can be in the form of neutral particles and charged particles (i.e., ions and electrons). Charged particles subject to electromagnetic forces at Mars. Ions, more gravitationally bounded than electrons, can be accelerated to escape velocities by these forces. One of the accelerating forces for ions at Mars is in the form of ambipolar electric field, produced by electron-ion separation. This study provides the first statistical analysis of amiboplar electric field at Mars with MAVEN data. Integrating this force over a spatial distance, the resulting potential, determined from MAVEN's measurements, ranges from 0 to -1.5 eV. These potentials can accelerate more ions to escape velocity and enhance ion escape. This study is cruel to characterize low-energy ion escape, an important atmospheric loss channel.