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Disentangling photoelectrons and penetrating solar wind electrons in the dayside Martian upper atmosphere

Presentation #215.06 in the session Planetary Space Physics Talks (Oral Presentation)

Published onOct 23, 2023
Disentangling photoelectrons and penetrating solar wind electrons in the dayside Martian upper atmosphere

In-situ produced photoelectrons and precipitating solar wind electrons are two distinct hot electron populations in the dayside Martian upper atmosphere. While each population has been known for decades, its relative contribution to the measured hot electron flux has not been adequately characterized up to now. In this study, we implement a two-stream kinetic model to compute the hot electron flux for the typical draped magnetic field configuration. By comparing model results to realistic data acquired by the Mars Atmosphere and Volatile Evolution mission, we show that the electron fluxes predicted by the pure photoelectron model are enormously underestimated, especially in the direction towards Mars, but the measurements can be adequately reproduced once solar wind electron precipitation is taken into account. Such a precipitation plays a crucial role above 200 km, not only for hot electrons at all energies that move towards Mars but also for electrons above 1000 eV that move away from Mars due to the backscattering of precipitating electrons. In contrast, the hot electron population is predicted to be mostly composed of photoelectrons below 200 km. The significance of precipitating solar wind electrons is also evaluated, revealing an appreciable impact on the structure of the dayside Martian upper atmosphere at high altitudes, where electron impact ionization is enhanced by a factor of 3 and cold electron heating enhanced by 50%.

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