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

Monte Carte models are used to describe the interaction between the inciden t pick-up ions and the Mars neutral atmosphere. The sputtered population in side the corona and escaping particles are described using a modified 3D te st 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 1-25), when c orrected for coronal ejection. It is also shown that the exobase altitude c an depend on sputtering. Two epochs of Mars history are simulated. For an e poch suggested to be about 2.5 Gyr ago, sputtering is at least as important as dissociative-recombination for populating the corona and the heating du e to the pick-up ion flux is of the same order as the EUV and UV beating of the thermosphere. For this epoch and present solar minimum conditions we p resent the distribution in the density and the energy of the sputtered part icles 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 th e most energetic regions. (C) 2001 Elsevier Science Ltd. All rights reserve d.