Terrestrial magma ocean evolution: Building an atmosphere under the young Sun.

The magma ocean is an early stage in the terrestrial planet evolution attributed to energy delivery by protoplanetary impacts and early radioactive elements’ decay. Its duration sets a period of particularly high temperatures at the surface (>1500 K), enough to melt the silicate mantle. Simultaneously, it enables massive volatile degassing from the interior. As such, the magma ocean thermal evolution controls the build up of the secondary atmosphere and the conditions at the surface. It is thus crucial to constrain its lifetime as it governs the mass and composition of the atmosphere which receives the early stellar XUV activity. We look at degassing of H2O and CO2, a volatile choice compatible with an oxidized mantle. A grey and a line-by-line atmosphere are alternatively used to resolve the coupled interior-atmosphere thermal evolution. In addition to other factors we find that the water vapour can decelerate substantially the magma ocean solidification. On the contrary, the lack of atmosphere or rapid escape thereof restricts its duration by two orders of magnitude. Since the degassing of H2O and CO2 from the interior does not occur simultaneously, qualitative switches of atmospheric composition from CO2 to H2O-dominated are expected, that could affect atmospheric escape processes