Impactor core breakup during impact into a magma ocean: A parameter study

Abstract

The present day concentrations of highly siderophile elements in Earth’s mantle cannot be sufficiently explained by planetary differentiation processes. Material from iron cores of large differentiated bodies, incorporated into a magma ocean due to impact during the late accretion phase, may offer an explanation for the increased abundance of highly siderophile elements, which are considered a measure of the late addition of material. For the chemical equilibration of metallic impactor core material with a silicate magma ocean it is important to know whether the core breaks up. It could shatter into fragments that mix with the magma ocean or penetrates the magma ocean as a coherent mass that does not equilibrate with the surrounding silicates. In order to quantify the fragmentation process between these two end-member cases we performed hydrocode simulations of differentiated impactors into magma oceans at different impactor sizes, impact velocities and magma ocean depths. For this, we developed and implemented a new disruption method into our simulation code, which allows for a more realistic and quantitative description than previously possible. We find that there is significant breakup of the impactor core, increasing with greater magma ocean depth, until the impactor core is completely fragmented at a depth of more than twice the impactor radius. If the magma ocean is shallower, large portions of the impactor core can reach the magma ocean bottom before fragmenting, hence avoiding chemical reequilibration with the surrounding silicates.