Mars' atmospheric evolution: 40Ar as a tracer

The noble gas 40Ar is one of the clues of Mars’ past history. It is thought to be an excellent tracer of sources and migration of volatiles in Mars’ crust, mantle and atmosphere (Breuer, European Mars Science and Exploration conference, November 2007). Its evolution depends on the degassing and volcanic histories as well as on the atmospheric escape to space. Degassing and volcanic histories will depend on the crust evolution whereas atmospheric escape is related to Mars’ interaction with the solar wind. In this paper, we will reconsider the different atmospheric escape mechanism efficiency, in particular by recalculating atmospheric loss induced by sputtering. We will then couple such mechanism to various scenarios of 40Ar degassing from the crust in particular taking into account the potential role of hydrothermalism of the crust as suggested by the recent discovery of Mars’ methane (Chassefière and Leblanc Planetary Science 2010). Such a calculation will allow us to derive what could have been the fate of Mars’ 40Ar.