Earth formation in the lab: metal-silicate equilibration and core stratification after planetary impacts.

Earth formed by successive collisions between planetary embryos, most of them formed of a metallic core and a silicate mantle. I will present laboratory experiments on the fluid dynamics of these collisions. Our experiments replicate the cratering process observed in impact simulations and inferred at the surface of terrestrial planets. Unlike simulations, experiments produce small-scales and turbulent mixing. We obtain scaling laws for mixing as a function of the velocity, size and density of the impactor. Applied to Earth formation, these scalings predict full chemical equilibration between the impactor core and the mantle silicates for impactors much smaller than the Earth. In contrast, we predict partial equilibration for giant impacts. Our results also indicate that the stratification inferred from seismic data at the top of Earth's core could be a vestige of the giant impact that formed the Moon.