On the elastic and inelastic collisions between precipitating energetic hydrogen atoms and Martian atmospheric neutrals

Abstract

Properties of elastic and inelastic processes in the Martian upper atmosphere caused by precipitating hydrogen atoms have been studied. The energetic (≲ 1 keV) neutral atoms, ENAs, are produced by the charge exchange process between the solar wind protons and the atoms in the Martian exosphere. The process gives a mechanism to deposit energy to the Martian atmosphere in addition to the well‐known EUV radiation. The energy deposition is studied by both a microscopic and a macroscopic model. The microscopic approach is based on Monte Carlo (MC) simulations which make it possible to study individual collisions and trajectories. The macroscopic approach utilizes the continuous slowing down approximation (CSDA). The CSDA equations are derived starting from the first principles in order to analyze the role of the backscattered particles. The MC and CSDA models are used to study how the energy deposition depends on the energy of precipitating ENAs and on the solar zenith angle. The role of the adopted scattering cross‐section models is analyzed, as well as differences between elastic and inelastic collisions. MC simulations suggest that the backscattered ENAs may play an important role in the energy deposition process. Comparisons between MC and CSDA models also illustrate that the CSDA model can give a relatively good approximation for the energy deposition profiles with a proper choice of the free parameters.