The terrestrial late veneer from core disruption of a lunar-sized impactor

TL;DR

This paper investigates how a massive, differentiated impactor could have delivered highly siderophile elements to Earth's mantle through core disruption and fragmentation during a late, oblique impact in the early Hadean era.

Contribution

It provides a detailed analysis of the mechanical and chemical processes that allow a lunar-sized impactor's core to deliver HSEs to Earth's mantle, highlighting the role of impact angle and fragmentation.

Findings

A single oblique impact can supply sufficient HSEs to Earth's mantle.

Impact core disintegrates into small metallic particles that oxidize and pollute the mantle.

Most impactor fragments re-accrete as secondary impactors with further fragmentation.

Abstract

Overabundances in highly siderophile elements (HSEs) of Earth's mantle can be explained by conveyance from a singular, immense (3000 km in a diameter) "Late Veneer" impactor of chondritic composition, subsequent to lunar formation and terrestrial core-closure. Such rocky objects of approximately lunar mass (about 0.01 M_E) ought to be differentiated, such that nearly all of their HSE payload is sequestered into iron cores. Here, we analyze the mechanical and chemical fate of the core of such a Late Veneer impactor, and trace how its HSEs are suspended - and thus pollute - the mantle. For the statistically most-likely oblique collision (about 45degree), the impactor's core elongates and thereafter disintegrates into a metallic hail of small particles (about 10 m). Some strike the orbiting Moon as sesquinary impactors, but most re-accrete to Earth as secondaries with further fragmentation. We show that a single oblique impactor provides an adequate amount of HSEs to the primordial terrestrial silicate reservoirs via oxidation of (<m-sized) metal particles with a hydrous, pre-impact, early Hadean Earth.