Predictions of the atmospheric composition of GJ 1132b

TL;DR

This study models GJ 1132b's atmospheric evolution, showing it likely has a water-derived, oxygen-rich atmosphere with a magma ocean, influenced by initial water content and hydrogen loss processes.

Contribution

It provides the first detailed modeling of GJ 1132b's atmospheric composition considering magma ocean interactions and hydrogen dissociation effects.

Findings

Most atmospheres are oxygen-dominated and tenuous.

Over 90% of produced O2 is lost to space.

High initial water content can lead to thick O2 atmospheres.

Abstract

GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly characterizable small exoplanets currently known. In this paper we study the interaction of a magma ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the magma ocean absorbs at most ~10% of the O2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our simulations is a tenuous atmosphere dominated by O2, although for very large initial water abundances atmospheres with several thousands of bars of O2 are possible. A substantial steam envelope would indicate either the existence of an earlier H2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further modeling is needed to study the evolution of CO2 or N2-rich atmospheres on GJ 1132 b.