Atmospheric Mass Loss from Hot Jupiters Irradiated by Stellar Superflares

Because of their activity, late-type stars are known to host powerful flares producing intense high-energy radiation on short timescales that may significantly affect the atmosphere of nearby planets. We employ a one-dimensional aeronomic model to study the reaction of the upper atmosphere of the hot Jupiter HD 209458b to the additional high-energy irradiation caused by a stellar flare. Atmospheric absorption of the additional energy produced during a flare leads to local atmospheric heating, accompanied by the formation of two propagating shock waves. We present estimates of the additional atmospheric loss occurring in response to the flare. We find the mass-loss rate at the exobase level to significantly increase (3.8 × 10¹⁰, 8 × 10¹⁰, and 3.5 × 10¹¹ g s^-1 for 10, 100, and 1000 times the high-energy flux of the quiet star, respectively) in comparison to that found considering the inactive star (2 × 10¹⁰ g s^-1).