Proton and hydrogen atom transport in the Martian upper atmosphere with an induced magnetic field

Abstract

We have applied the Direct Simulation Monte Carlo method to solve the kinetic equation for the H/H+ transport in the upper Martian atmosphere. We calculate the upward H and H+ fluxes, values that can be measured, and the altitude profile of the energy deposition to be used to understand the energy balance in the Martian atmosphere. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. We use an energy spectrum of the down moving protons in the altitude range 355-437 km adopted from the Mars Express Analyzer of Space Plasma and Energetic Atoms measurements in the range 700 eV-20 keV. The particle and energy fluxes of the downward moving protons were equal to 3.0 × 106 cm-2 s-1 and 1.4 × 10-2 erg cm-2 s -1. It was found that 22% of particle flux and 12% of the energy flux of the precipitating protons is backscattered by the Martian upper atmosphere, if no induced magnetic field is taken into account in the simulations. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85-500 km, we find that up to 40%-50% of the energy flux of the precipitating protons is backscattered depending on the velocity distribution of the precipitating protons. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.