Early evolution and habitability of rocky planets
Séminaires Planétologie et Sciences Spatiales
522, bât. Lamarck
At the end of the accretion phase a combination of heat sources such as the energy brought by giant impacts, radioactive decay of short-period elements, and metal-silicate differentiation, point to the occurrence of early molten stages on terrestrial planets. The cooling and solidification of this early so-called "magma ocean" strongly influences the earliest compositional differentiation and volatile distribution of the planet. Indeed, this common early evolution stage of rocky planets witnesses the degassing of the atmosphere and sets the initial conditions for the long-term evolution of the planets. It is thus of major importance in understanding the formation of the primitive water ocean, the onset of thermally driven mantle convection and the diversity of observed terrestrial planets. Using a coupled magma ocean-atmosphere thermal evolution model, we investigated the cooling of the planet and the surface conditions reached at the end of this early stage. Here, I present how the initial volatile content (namely CO2 and H2O contents), and the distance from the star influence the formation of a water ocean at the end of the cooling, for both cloud-free and cloudy atmospheres. The presence of a thick cloud cover extends clement surface conditions close to the star, potentially allowing for water ocean formation on early Venus. The effect of the host star temperature and of the planetary mass on the location of the habitable zone will also be discussed.