Impact of out-of-equilibrium degassing of magma oceans on volatile trapping, solidification time and habitability

Rocky planets such as the Earth or Venus likely experienced at least one magma ocean (MO) episode, during which the silicate mantle was molten in part or in full due to the heat generated by accretion and radioactive heating. During this MO stage, volatile elements present in the magma degassed to form the secondary atmosphere. Better understanding this degassing process can help us constrain the duration of the MO stage, the volatile enrichment of the subsequent mantle and the conditions for habitability. 

The degassing process is typically assumed to be efficient, in equilibrium with the atmosphere: instant degassing of oversaturated fluid parcels in a well-mixed magma ocean. However, MO parcels may experience considerable delay in reaching the shallow pressures where bubbles can form and degas into the atmosphere.

We take into account this out-of-equilibrium degassing in a 1D interior model coupled to a radiative-convective CO2/H2O atmosphere. The model is parameterized using scaling laws derived from joint laboratory and numerical experiments. We explore a broad range of planet sizes, stellar radiation and CO2 and H2O initial concentrations, and examine the impact of rapid rotation akin to that of the early Earth.

Using this coupled model, we explore the impact of out-of-equilibrium degassing on atmospheric composition and habitability, the cooling time of the MO, and the volatiles trapped in the mantle.