Persistence of Flare-Driven Atmospheric Chemistry on Rocky Habitable Zone Worlds

TL;DR

This study uses 3D models to show how stellar flares influence the atmospheric chemistry of rocky exoplanets, revealing potential biosignature signals that could be detected by future telescopes.

Contribution

It demonstrates the persistent chemical effects of stellar flares on exoplanet atmospheres across different star types using coupled climate-chemistry simulations.

Findings

Flares cause K- and M-dwarf atmospheres to deviate from equilibrium, G-dwarfs recover quickly.

Flares produce similar nitric oxide levels in O2-rich and O2-poor atmospheres.

Bio-indicating species' transmission features may be detectable after stellar flares.

Abstract

Low-mass stars show evidence of vigorous magnetic activity in the form of large flares and coronal mass ejections. Such space weather events may have important ramifications for the habitability and observational fingerprints of exoplanetary atmospheres. Here, using a suite of three-dimensional coupled chemistry-climate model (CCM) simulations, we explore effects of time-dependent stellar activity on rocky planet atmospheres orbiting G-, K-, and M-dwarf stars. We employ observed data from the MUSCLES campaign and Transiting Exoplanet Satellite Survey and test a range of rotation period, magnetic field strength, and flare frequency assumptions. We find that recurring flares drive K- and M-dwarf planet atmospheres into chemical equilibria that substantially deviate from their pre-flare regimes, whereas G-dwarf planet atmospheres quickly return to their baseline states. Interestingly, simulated O$_2$-poor and O$_2$-rich atmospheres experiencing flares produce similar mesospheric nitric oxide abundances, suggesting that stellar flares can highlight otherwise undetectable chemical species. Applying a radiative transfer model to our CCM results, we find that flare-driven transmission features of bio-indicating species, such as nitrogen dioxide, nitrous oxide, and nitric acid, show particular promise for detection by future instruments.