Title:
Primordial Evolution of Terrestrial Planets: From Magma Ocean to
Temperate Surface Conditions

Abstract:
How the volatile content influences the primordial surface
conditions of terrestrial planets, and thus, their future geodynamic
evolution, is an important question to answer. Characterising the cooling
and solidification of the early magma ocean phase (MO), which controls
atmosphere formation, might help in understanding the diversity of rocky
planets.
We simulate the secular convective cooling of a 1-D magma ocean in
interaction with its outgassed atmosphere. A first rapid cooling stage,
where efficient MO cooling and degassing take place, producing the
atmosphere, is followed by a second quasi steady-state regime where the
heat flux balance is dominated by the solar flux. The end of the rapid
cooling stage (ERCS) is reached when the mantle heat flux becomes
negligible compared to the absorbed solar flux.
Varying the initial CO2 and H2O contents and the solar distance, for both
clear-sky and cloudy atmospheres, we will see that the resulting surface
conditions at ERCS strongly depend on these parameters and that water ocean
formation obeys simple scaling laws. Interestingly, when considering a
thick cloud cover, a water ocean is likely to be formed on early Venus as
soon as the initial water content exceeds a 0.1 Earth ocean mass. Thus, the
Earth and Venus might not be so different at the end of the magma ocean
stage.
Extending this approach to exoplanets orbiting stars with temperatures and
radii different from our Sun allows us to examine different scenarios of
early water ocean formation out of the solar system and characterise their
habitability.
Far from the star and depending on the volatile content, possible rapid
solidification and cooling might induce large stresses to the lithosphere
due to thermal contraction. If those stresses exceed the lithospheric
strength, the lithosphere could break and subduct. Laboratory experiments
run in complex fluids show this very behaviour that might play a
significant role for the transition from magma ocean to a
subduction-dominated regime.