How Flares regulate Atmospheric Losses from the TRAPPIST-1 planets

Stellar flares are considered an impediment to habitability, especially in the case of close-in exoplanets around M-dwarfs since these stars are highly active. In recent times, there has been a growing awareness that coronal mass ejections (CMEs) - sometimes termed as stellar storms or superstorms, depending on the flare energy - associated with stellar flares pose severe threats to planetary habitability. Interplanetary CMEs (or ICMEs), corresponding to fast-moving magnetic clouds, act to impact the planets with significantly high dynamic pressure. Semi-analytical models imply that planets around active stars ( 1 flare/day) may experience escape rates that are 1-3 orders of magnitude higher than those arising from erosion by stellar winds alone. Understanding atmospheric escape is very important from the standpoint of habitability since atmospheric evolution influences the climate and the fluxes of ionizing radiation reaching the surface, among other factors. Here we carry out sophisticated 3D multi-species MHD simulations to assess how the atmospheric escape rates of the TRAPPIST-1 planets evolve during the passage of an ICME, where the ICME is initialized and modeled according to the flare observations.