A colossal impact enriched Mars' mantle with noble metals

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.

Accepted for publication in Geophysical Research Letters

References in corpus (2)

• Formation of Phobos and Deimos via a Giant Impact
• Late veneer and late accretion to the terrestrial planets

Cited by in corpus (5)

• The terrestrial late veneer from core disruption of a lunar-sized impactor
• Impact bombardment chronology of the terrestrial planets from 4.5 Ga to 3.5 Ga
• Did Mars possess a dense atmosphere during the first ~400 million years?
• Mars in the aftermath of a colossal impact
• A new estimate for the age of highly-siderophile element retention in the lunar mantle from late accretion