A special giant impact model: implications on core-mantle chemical differentiation

Abstract

The Earths core formation process has decisive effect in the chemical differentiation between the Earths core and its mantle. Here, we propose a new core formation model which is caused by a special giant impact. This model suggests that the impactors core can be kept intact by its own sticky mantle under appropriate impacting conditions and let it merge into the targets core without contact with the targets mantle. We call this special giant impact that caused the new core formation mode as glue ball impact model (GBI). By simulating hundreds of giant impacts with the sizes from planetesimals to planets, the conditions that can lead to GBI have been found out. If with small impact angle (i.e., less than 20 degree), small impact velocity and small impactors mass but larger than 0.07 Mearth, there is a good chance to produce a GBI at the final stage of the Earths accretion. We find that it will be much easier to have GBIs at the late stage of the Earths accretion rather than at the early stage of it. The GBI model will pose a great challenge to many problems between the equilibrium of Earths core and mantle. It provides an additional source for the excess of highly siderophile elements in the Earths mantle and also brings excessive lithophile elements to the Earths core. The GBI model may shed light on the study of Moon-formation and chemical differentiations of the pro-Earth.