Minimum Radii of Super-Earths: Constraints from Giant Impacts

TL;DR

This paper uses giant impact simulations to establish a conservative lower radius boundary for super-Earths, aiding interpretation of their composition and formation history.

Contribution

It introduces a novel application of impact simulations to constrain the minimum radii of super-Earths based on collisional mantle stripping.

Findings

Provides a conservative minimum radius boundary for super-Earths.

Offers a testable prediction for Kepler planet observations.

Highlights the degeneracy in interior structure models.

Abstract

The detailed interior structure models of super-Earth planets show that there is degeneracy in the possible bulk compositions of a super-Earth at a given mass and radius, determined via radial velocity and transit measurements, respectively. In addition, the upper and lower envelopes in the mass--radius relationship, corresponding to pure ice planets and pure iron planets, respectively, are not astrophysically well motivated with regard to the physical processes involved in planet formation. Here we apply the results of numerical simulations of giant impacts to constrain the lower bound in the mass--radius diagram that could arise from collisional mantle stripping of differentiated rocky/iron planets. We provide a very conservative estimate for the minimum radius boundary for the entire mass range of large terrestrial planets. This envelope is a readily testable prediction for the population of planets to be discovered by the Kepler mission.