Origin and solar activity driven evolution of Mars' atmosphere

Abstract

The evolution of the martian atmosphere and its H 2 O inventory can be divided into early and late evolutionary epochs. Volatiles such as H 2 O and CO 2 could have built up a dense water vapour dominated H 2 O/CO 2 steam atmosphere during the early impact and magma ocean solidification period. Due to the high activity of the young Sun, Mars' atmosphere experienced soft X-ray and EUV-driven hydrodynamic blowoff during the early Noachian, which could have powered the loss of an outgassed initial steam atmosphere with a surface pressure of ≥ 100 bar. After this initial atmosphere was lost, impacts and mantle outgassing during later evolutionary epochs may have built up around ∼4±0.2 Gyr ago, a CO 2 atmosphere which could have been denser than the present ∼7 mbar. The CO 2 surface pressure of such a secondary atmosphere and its evolution followed a complex interplay of various nonthermal escape processes and carbonate precipitation. Finally we discuss how the discovery of transiting terrestrial exoplanets will open the possibility to test atmospheric evolution hypotheses as discussed in our study by observations and advanced numerical models.