Atmospheric effects of precipitating energetic hydrogen atoms on the Martian atmosphere

The Martian atmosphere is under the influence of an intense flux of precipi tating energetic (less than or similar to 1 keV) hydrogen atoms. In the sol ar wind and in the magnetosheath, fast hydrogen atoms are produced by charg e exchange between solar wind protons and the hydrogen corona. Atmospheric effects of the precipitating hydrogen atoms are thus manifestations of the direct interaction between solar wind protons and the planetary neutrals. A three-dimensional Monte Carlo simulation model has been developed to study different atmospheric effects of the precipitating hydrogen atoms. The mod el is used to calculate the altitude profiles of the energy deposition rate s, the ion production rates, and the photon emission rates at different sol ar zenith angles under low solar activity conditions. The peak loss and pro duction rates under typical solar wind conditions caused by precipitating h ydrogen atoms are estimated to be similar to1% of the corresponding peak va lues due to extreme ultraviolet radiation but comparable or larger than eff ects of H+ and O+ precipitation at low altitudes. The results indicate that a substantial part of the incoming particle and energy flux is scattered b ack from the Martian atmosphere.