Investigation of hydrogen exosphere from foreshock electron impact ionization at Mars
Abstract
The electron spectrometer SWEA on board the MAVEN spacecraft orbiting Mars often measures backstreaming electrons emanating from the bow shock when located inside the foreshock. They display a systematic flux fall off with the distance from the shock along the magnetic field direction which was unexpected, since not observed at other planetary foreshocks so far including the terrestrial one. It has been shown recently that this can be explained by impact ionization of exospheric neutral hydrogen atoms and that the flux decay is consistent with the electron-atomic hydrogen impact cross-section for a large range of energy. The relative variation of the electron flux gives an insight into the far exosphere compared to other methods to investigate the neutral environment. It basically reproduces as expected the seasonality for the hydrogen though other variations are often superimposed. Moreover, there is a sharp variation of the pickup protons - generated ULF waves amplitude when crossing the electron foreshock boundary as well as a decrease of this amplitude correlated with the increasing distance from the shock along the magnetic field. This shows that foreshock electrons play an important role in locally increasing the number of pickup ions which contribute to the atmospheric escape.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..2110434M