Stellar flares have been observed to produce a burst of radiation over a wide range of wavelengths, among which X-rays and EUV constitute the major ionizing stellar radiation for planetary atmospheres at low and high altitudes, respectively. 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. At the same time, there has been a growing awareness that coronal mass ejections (CMEs) — sometimes termed as stellar storms — associated with stellar flares pose severe threats to planetary atmospheric retention. It is evident that understanding atmospheric escape is vital from the standpoint of habitability since atmospheric evolution influences the climate and the fluxes of ionizing radiation reaching the surface, among other factors.Until now, there have been no systematic studies of the impact of stellar flares and associated storms on exoplanetary atmospheric losses despite their indubitable occurrence and pertinence. Here, we carry out sophisticated 3D MHD simulations (that includes important photochemistry) to assess how the atmospheric escape rates of the TRAPPIST-1 planets evolve during 1) a 1033 erg flare (based on observations) without a CME (where the CME may be suppressed or deviated from the planet) and, 2) a 1033 erg flare with a CME, where the CME is initialized and modeled according to the flare energy by using a stellar wind model. We found that the atmospheric escape rates are enhanced by 1-3 orders of magnitude compared to our previous study that used normal stellar wind conditions. For the outmost TRAPPIST-1h, if such flares occur at a frequency of 1 per day, a 1-bar atmosphere will be scavenged on the time scale of 100 million years. This time scale reduces to 1 million years for the innermost TRAPPIST-1b. This represents the first study where the roles of stellar flares and storms on exoplanetary atmospheric escape for the TRAPPIST-1 planets are clearly elucidated. The new results obtained herein would be of considerable interest to a wide audience and thus deserving an oral presentation.
AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019