Equilibrated crater: fragmentation and mixing

Abstract

The composition of the Earth's mantle, built by impacts of metallic core planetesimals, depends on the time offered to metal–silicate equilibration (concentration equalization by mixing) as the impactor fragments settle down. Smaller fragments equilibrate while bigger ones remain segregated and accumulate in the – therefore iron rich – Earth's core. To understand the primary instability setting the interpenetration depth and wavelength between the impactor and the mantle, Lherm et al. (J. Fluid Mech., vol. 937, 2022, A20) analyse the intermingled phenomena occurring when a drop impacts a substrate of a pool of another liquid, digging a crater. The density difference between the phases triggers a Rayleigh–Taylor instability when the drop is denser than the pool. The overall planet chemical composition relies on a tradeoff between fragmentation and mixing; this study provides elements to decipher their relative importance.