The Early Evolution of Exoplanetary Systems
Adina Feinstein (Dept. of Physics & Astronomy, Michigan State University)

Within the past decade, we have discovered only a dozen young (< 300 Myr) short-period exoplanets, compared to the ~6,000 mature systems. 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 X-ray and ultraviolet (XUV) stellar irradiation. These effects are intensified in the earliest stages of planetary evolution, when young stars are more active and produce extreme XUV 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 early results of the characterization of eight young short-period exoplanets and observed with JWST. I will present trends we have uncovered in atmospheric composition as a function of age and highlight our search for ongoing atmospheric escape. Beyond the planets, I will present what we have been able to learn about the young host stars with these new high-precision observations. Understanding these properties is essential not only for correcting transmission spectra but for defining the environments that shape the fate of the exoplanet population we see today.