The Response of Planetary Atmospheres to the Impact of Icy Comets I: Tidally-Locked exo-Earths

TL;DR

This study models how icy comet impacts influence the atmosphere of tidally-locked Earth-like exoplanets, revealing changes in chemistry, climate, and potential habitability observable over years.

Contribution

It introduces a coupled impact and climate model to analyze the atmospheric effects of icy comet impacts on exoplanets, highlighting water's role in atmospheric changes.

Findings

Water impacts atmospheric opacity and temperature structure.

Ozone column density decreases by about 10%.

Impact effects are observable for 1-2 years post-impact.

Abstract

Impacts by rocky and icy bodies are thought to have played a key role in shaping the composition of solar system objects, including the Earth's habitability. Hence, it is likely that they play a similar role in exoplanetary systems. We investigate how an icy cometary impact affects the atmospheric chemistry, climate, and composition of an Earth-like, tidally-locked, terrestrial exoplanet, a prime target in the search for a habitable exoplanet beyond our solar system. We couple a cometary impact model which includes thermal ablation and pressure driven breakup with the 3D Earth System Model WACCM6/CESM2, and use this model to investigate the effects of the water and thermal energy delivery associated with an $R=2.5$ km pure water ice cometary impact on an Earth-like atmosphere. We find that water is the primary driver of longer timescale changes to the atmospheric chemistry and composition by acting as a source of opacity, cloud ice, and atmospheric hydrogen/oxygen. The water opacity drives heating at $\sim5\times10^{-4}$ bar, and cooling below, due to a decreased flux reaching the surface. The increase in atmospheric hydrogen and oxygen also drives an increase in the abundance of hydrogen/oxygen rich molecules, with the exception of ozone, whose column density decreases by $\sim10\%$. These atmospheric changes are potentially observable for $\sim$ 1-2 years post-impact, particularly those associated with cloud ice scattering. They also persist, albeit at a much reduced level, to our quasi-steady-state, suggesting that sustained bombardment or multiple large impacts have the potential to shape the composition and habitability of terrestrial exoplanets.