NONLINEAR MHD WAVES AND DISCONTINUITIES IN THE MARTIAN MAGNETOSHEATH - OBSERVATIONS AND 2D BI-ION MHD SIMULATIONS

The characteristic scale of the Martian magnetosheath is less than the pick-up gyroradius of oxygen ions. This leads to admissible different ial motion of protons and heavies and a strong coupling between both i on fluids. 2D bi-ion MHD simulations reveal many new interesting featu res in such Large Larmour Radius systems. The formation of an ion-comp osition boundary, which separates both plasmas, and structuring of the transition from proton dominated plasma of the solar wind origin to m assive planetary plasma are the main features of the interaction. A co mprehensive multi-instrument study of Martian plasma environment and t he comparison with theoretical modelling initiated in the framework of the Visiting Science Programme of the International Space Science Ins titute (ISSI) in Bern (Switzerland) gives confirmation that Mars inter acts with the solar wind like a comet which has a outgassing rate near to that of Grigg-Skjellerup. The results may also be relevant for sma ll bodies which are surrounded by a neutral gas atmosphere (icy moons, asteroids, Mercury).