Giant Impact Events for Protoplanets: Energetics of Atmospheric Erosion by Head-on Collision

TL;DR

This study uses hydrodynamic simulations to analyze how head-on giant impacts during planet formation can cause atmospheric erosion, providing insights into the atmospheric diversity of super-Earths and rocky planets.

Contribution

It introduces a relationship between impact energy and atmospheric loss, highlighting the role of giant impacts in shaping planetary atmospheres during formation.

Findings

Atmospheric escape energy is proportional to impact and gravitational energies.

Head-on impacts with similar-mass planets significantly erode atmospheres.

Impacts constrain formation scenarios for planets with substantial atmospheres.

Abstract

Numerous exoplanets with masses ranging from Earth to Neptune and radii larger than Earth have been found through observations. These planets possess atmospheres that range in mass fractions from 1% to 30%, reflecting the diversity of atmospheric mass fractions. Such diversities are supposed to be caused by differences in the formation processes or evolution. Here we consider head-on giant impacts onto planets causing atmosphere losses in the later stage of their formation. We perform smoothed particle hydrodynamic simulations to study the impact-induced atmosphere loss of young super-Earths with 10%-30% initial atmospheric mass fractions. We find that the kinetic energy of the escaping atmosphere is almost proportional to the sum of the kinetic impact energy and self-gravitational energy released from the merged core. We derive the relationship between the kinetic impact energy and the escaping atmosphere mass. The giant impact events for planets of comparable masses are required in the final stage of the popular scenario of rocky planet formation. We show it results in a significant loss of the atmosphere, if the impact is a head-on collision with comparable masses. This latter fact provides a constraint on the formation scenario of rocky planets with substantial atmospheres.