Abstract

Within the past decade, we have discovered only a dozen young (< 300 Myr) short-period exoplanets, compared to ~5,600 mature exoplanets. The radii of these young planets are larger than older planets on similar orbital periods. The leading hypothesis is that these young planets have inflated atmospheres because they are still contracting. Inflated atmospheres are more susceptible to photoevaporation — atmospheric removal driven by high energy stellar irradiation. These effects are intensified in the earliest stages of planetary evolution, when young stars are more active and produce extreme levels of X-ray and Ultraviolet (UV) radiation on a variety of timescales. Even though it is challenging to study exoplanets around active stars, observational constraints of these targets provide crucial insights into our understanding of exoplanet formation and evolution. In this talk, I will present several benchmark studies of young stars and their planets spanning from the UV to the infrared (IR). I will present the results of several large statistical surveys of stellar flares with the Transiting Exoplanet Survey Satellite, and detailed characterization of stellar flares with the Hubble Space Telescope. I will present atmospheric follow-up characterization of young short-period exoplanets in the UV, optical, near-IR, and IR. Finally, I will present models of flare-driven atmospheric escape, discuss the contributions of stellar flares in removing gas-dominated planetary atmospheres, and highlight future steps in understanding these challenging young systems.