Retracing the condensation of the protolunar disk
from ab initio atomistic simulations 
Razvan Caracas
CNRS, ENS de Lyon, Laboratoire de Géologie de Lyon, Lyon, France razvan.caracas@ens-lyon.fr

We investigate the thermodynamics of the Giant impact and the evolution of the protolunar disk until the condensation of the Magma Ocean. For this, we employ first-principles molecular dynamics simulations to understand the physical and chemical behavior of the different parts of the disk, at the atomic level. We consider pyrolite (=bulk silicate Earth) and pure iron to differentiate and compare the behavior of the two major parts of the disk: the silicate mantle(s) and the iron core(s). We cover the 0.25 – 15 g/cm3 density range and 2000 – 15000 K temperature range. 
Based on the computed Hugoniot equations of state we predict that after the shock the thermodynamic conditions in the disk easily raise up to hundreds of GPa and more than 10000K. At these conditions both silicates and iron are supercritical, the fluids are highly diffusive, and short-lived small atomic clusters dominate the chemical speciation. 
We find that the critical points lie at relatively low density and high temperatures. Our results are lower than the extrapolations considered so far in impact simulations using the (M-)ANEOS database. They suggest that most of the condensation of the Earth into a magma ocean takes place in supercritical conditions. The pressures and temperatures are high enough to maintain a continuous interface between the magma ocean and the atmosphere. This would have prolonged the chemical exchange and equilibration between the different parts of the disk for a longer time.