Atmospheric effects of precipitating energetic hydrogen atoms on the Martian atmosphere

The Martian atmosphere is under the influence of an intense flux of precipitating energetic (less than or similar to 1 keV) hydrogen atoms. In the solar wind and in the magnetosheath, fast hydrogen atoms are produced by charge 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 model is used to calculate the altitude profiles of the energy deposition rates, the ion production rates, and the photon emission rates at different solar zenith angles under low solar activity conditions. The peak loss and production rates under typical solar wind conditions caused by precipitating hydrogen atoms are estimated to be similar to1% of the corresponding peak values due to extreme ultraviolet radiation but comparable or larger than effects of H+ and O+ precipitation at low altitudes. The results indicate that a substantial part of the incoming particle and energy flux is scattered back from the Martian atmosphere.