Sputtering of the Martian atmosphere by solar wind pick-up ions

Abstract

Monte Carlo models are used to describe the interaction between the incident pick-up ions and the Mars neutral atmosphere. The sputtered population inside the corona and escaping particles are described using a modified 3D test particle model, whereas, the heating effect due to the incident flux is described using a 2D Direct Simulation Monte Carlo. These results show that the standard 1D models overestimate the sputtering yield (by 15–25%), when corrected for coronal ejection. It is also shown that the exobase altitude can depend on sputtering. Two epochs of Mars history are simulated. For an epoch suggested to be about 2.5 Gyr ago, sputtering is at least as important as dissociative-recombination for populating the corona and the heating due to the pick-up ion flux is of the same order as the EUV and UV heating of the thermosphere. For this epoch and present solar minimum conditions we present the distribution in the density and the energy of the sputtered particles in Mars corona. In particular we show that the polar and dusk regions are the most dense regions and the shadow of the dawn and polar regions the most energetic regions.