A Collisional Origin to Earth's Non-chondritic Composition?

TL;DR

This study uses advanced collision modeling in N-body simulations to explore how Earth's non-chondritic composition could result from collisional erosion of differentiated planetesimals during planetary formation.

Contribution

It demonstrates that collisional mantle stripping can produce Earth-like Mg/Fe and Si/Fe ratios, highlighting the role of collisional differentiation in Earth's composition.

Findings

Mantle material can be stripped during planet formation.

Protoplanets can attain Earth's composition ratios.

Collisional erosion influences planetary core-mantle ratios.

Abstract

Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd/144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (> 100 km) up to isolation mass (> 0.16 M_Earth). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.