Monte Carlo Simulations of the Interaction of Fast Proton and Hydrogen Atoms With the Martian Atmosphere and Comparison With In Situ Measurements

We present model results of the interaction of proton and hydrogen atom precipitation with the Martian atmosphere. We use a kinetic Monte Carlo model developed earlier for the analysis of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) Mars Express data. With the availability of MarsAtmosphere and Volatile Evolution Mission in situ measurements, not only the flux of protons incident on theatmosphere but also their degradation along the orbit may now be described. The comparison of thesimulations with data collected with the Solar Wind Ion Analyzer shows that the Monte Carlo modelreproduces some of the measured features. The results of comparison between simulations andmeasurements of the proton fluxes at low altitudes make it possible to infer the efficiency of chargeexchange between solar wind and the extended hydrogen corona if the value of the magnetic field ismeasured simultaneously. We also find that the induced magnetic field plays a very important role in theformation of the backscattered flux and strongly controls its magnitude. At the same time, discrepancies between the modeled and the measured energy spectra of the backscattered protons are pointed out. We suggest that some of the physical processes controlling the upward flux are not fully understood or that the data processing of the measured backscattered proton flux should be improve