A colossal impact enriched Mars' mantle with noble metals

TL;DR

This paper suggests that a colossal impact event significantly enriched Mars' mantle with noble metals, explaining its hemispheric dichotomy and linking it to early planetary differentiation and satellite formation.

Contribution

It introduces the hypothesis that a giant impact contributed to Mars' noble metal enrichment and hemispheric dichotomy, providing estimates of impactor size and timing.

Findings

Mars' mantle contains 0.8 wt.% HSEs from late accretion.

A 1200 km diameter impactor is needed before 4430 Ma.

The impact may explain Mars' hemispheric dichotomy and satellite origin.

Abstract

Once the terrestrial planets had mostly completed their assembly, bombardment continued by planetesimals left-over from accretion. Highly siderophile element (HSE) abundances in Mars' mantle imply its late accretion supplement was 0.8 wt.%; Earth and the Moon obtained an additional 0.7 wt.% and 0.02 wt.%, respectively. The disproportionately high Earth/Moon accretion ratio is explicable by stochastic addition of a few remaining Ceres-sized bodies that preferentially targeted Earth. Here we show that Mars' late accretion budget also requires a colossal impact, a plausible visible remnant of which is the hemispheric dichotomy. The addition of sufficient HSEs to the martian mantle entails an impactor of at least 1200 km in diameter to have struck Mars before ca. 4430 Ma, by which time crust formation was well underway. Thus, the dichotomy could be one of the oldest geophysical features of the martian crust. Ejected debris could be the source material for its satellites.