Foreshock Electron Impact Ionization at Mars: Consequence on Neutral Exosphere
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. Though the absolute variation of the ionization rate is rather small compared to other processes and the relative reduction of neutral hydrogen density is negligible, some of these pickup ions may also impact the atmosphere at a much lower altitude and contribute to the atmospheric escape by the sputtering process.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P54C..02M
- Keywords:
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- 2437 Ionospheric dynamics;
- IONOSPHEREDE: 2459 Planetary ionospheres;
- IONOSPHEREDE: 5435 Ionospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5443 Magnetospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS