Stellar Winds Drive Strong Variations in Exoplanet Evaporative Outflows and Transit Absorption Signatures

TL;DR

This study uses 3D magnetohydrodynamic simulations to show how stellar wind interactions significantly influence exoplanet atmospheric outflows and their observable transit signatures, especially around M dwarf systems like TRAPPIST-1.

Contribution

It provides the first detailed modeling of stellar wind effects on exoplanet atmospheres and their Lyman-alpha transit signatures, highlighting the variability caused by wind conditions.

Findings

Stellar wind drags and accelerates planetary outflows.

Magnetosphere morphology varies with wind conditions.

Lyman-alpha transit signatures are highly variable on short timescales.

Abstract

Stellar wind and photon radiation interactions with a planet can cause atmospheric depletion, which may have a potentially catastrophic impact on a planet's habitability. While the implications of photoevaporation on atmospheric erosion have been researched to some degree, studies of the influence of the stellar wind on atmospheric loss are in their infancy. Here, we use three-dimensional magnetohydrodynamic simulations to model the effect of the stellar wind on the magnetosphere and outflow of a hypothetical planet, modeled to have an H-rich evaporating envelope with a pre-defined mass loss rate, orbiting in the habitable zone close to a low-mass M dwarf. We take the TRAPPIST-1 system as a prototype, with our simulated planet situated at the orbit of TRAPPIST-1e. We show that the atmospheric outflow is dragged and accelerated upon interaction with the wind, resulting in a diverse range of planetary magnetosphere morphologies and plasma distributions as local stellar wind conditions change. We consider the implications of the wind-outflow interaction on potential hydrogen Lyman-alpha (Lya) observations of the planetary atmosphere during transits. The Lya observational signatures depend strongly on the local wind conditions at the time of the observation and can be subject to considerable variation on timescales as short as an hour. Our results indicate that observed variations in exoplanet Lya transit signatures could be explained by wind-outflow interaction.