Collisional Stripping and Disruption of Super-Earths

TL;DR

This paper uses hydrodynamics simulations to study high-velocity collisions between super-Earths, revealing how such impacts can lead to planetary disruption, compositional changes, and different collision regimes during planet formation.

Contribution

It provides new criteria for catastrophic disruption, transition energy, and a scaling law for compositional changes in super-Earth collisions.

Findings

Disruption occurs at high velocities, small impact parameters, or small projectile mass.

Derived criteria for catastrophic disruption and transition energy.

Established a scaling law for compositional changes due to mantle stripping.

Abstract

The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to ~5 v_esc) collisions between 1 and 10 M_Earth planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.