The Unique Ability Of The Hubble Space Telescope To Characterize Young Exoplanet Environments

Modified Pass et al. (2025) Figure 2 showing an updated Cosmic Shoreline for exoplanets orbiting full convective M dwarfs. The exoplanets shift significantly along the y-axis depending on their assumed XUV history (specifically showing Pass et al. 2025 and Zahnle & Catling 2017), which changes the location of the Cosmic Shoreline. — astro-ph.IM

The Unique Ability Of The Hubble Space Telescope To Characterize Young Exoplanet Environments. The chemical and mass evolution of exoplanet atmospheres is shaped by their specific X-ray through ultraviolet (5 – 3200 Angstroms) irradiance history. X-ray and EUV (5 – 911 Angstroms) radiation largely contributes to atmospheric heating via photoionization, while far- and near-UV emission (912 – 3200 Angstroms) drives photochemistry. The (uncharacterized) variance between young star spectra in this wavelength range for the same spectral type causes significant uncertainty in interpreting present-day transmission spectra of young exoplanets, directly impacting the science return of the James Webb Space Telescope and other programs. Additionally, the lack of direct X-ray through UV characterization for stars of all ages leads to large uncertaint...