Can metal-rich worlds form by giant impacts?

TL;DR

This paper investigates whether giant impacts can produce metal-rich exoplanets and finds that such impacts are unlikely to account for the observed high-density planets, suggesting alternative formation processes.

Contribution

It combines orbital dynamics and impact physics to evaluate the likelihood of mantle stripping in super-Earths, challenging previous assumptions about their origins.

Findings

Giant impacts are unlikely to strip mantles sufficiently in super-Earths.

Most high-density exoplanets are probably not remnants of giant impacts.

Mantle stripping efficiency decreases with increasing planetary size.

Abstract

Planets and stars are expected to be compositionally linked because they accrete from the same material reservoir. However, astronomical observations revealed the existence of exoplanets whose bulk density is far higher than what is expected from host-stars' composition. A commonly-invoked theory is that these high-density exoplanets are the metallic cores of super-Earth-sized planets whose rocky mantles were stripped by giant impacts. Here, by combining orbital dynamics and impact physics, we show that mantle-stripping giant impacts between super-Earths are unlikely to occur at rates sufficient to explain the observed size and currently estimated abundance of the high-density exoplanets. We explain this as the interplay of two main factors: the parent super-Earths being in most cases smaller than 2 Earth radii; and the efficiency of mantle stripping decreasing with increasing planetary size. We conclude that most of the observed high-density exoplanets are unlikely to be metal-rich giant-impact remnants.