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

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.

Simultaneous Multiwavelength Flare Observations of EV Lacertae

“…High energy radiation may have adverse effects on the thermo-chemical equilibrium of the planets' atmospheres. This has many consequences including the loss of surface water, stripping of the planet's entire atmosphere or destruction of the ozone layer (Lammer et al 2007;Segura et al 2010;Bolmont et al 2017;Tilley et al 2019;Chen et al 2020). To fully account for the impact of M dwarf flares on exoplanet atmospheres, we must constrain the total energy emitted during the flares on M dwarfs at various wavelengths.…”