The Need for a Comprehensive Time-domain UV Spectral Survey of Stars and UV-SCOPE’s Mission to Obtain It

With the JWST deployed, new discoveries on the nature of exoplanets, gaseous to rocky, hot to cold, are just around the corner. For these planets, a key input shaping their atmospheric composition, stability, habitability, and biosignatures is the stellar ultraviolet (UV) radiation incident upon them. This radiative input can be directly measured from space given a sufficiently capable observatory. In this talk, we review recent work revealing scenarios where interpretations of terrestrial atmospheric spectra are vulnerable to persistent unknowns in the time-variability of stellar UV radiation. To address this vulnerability, we make the case for conducting a next-generation survey of dominant sources of stellar UV variability: stochastic flares, rotation, activity cycles, and age-activity evolution. The mid-class explorer mission concept, UV-SCOPE (Ultraviolet Spectroscopic Characterization Of Planets and their Environments), proposed December of 2021, would carry out this survey as one of three primary science goals. Further, it will provide the critical UV capability, currently available only with the aging Hubble Space Telescope, to couple the transit observation of an exoplanet (e.g., by the JWST) with contemporaneous or even simultaneous measurements of the incident UV emission from the host star. This talk will touch on planetary atmospheric sensitivities to UV radiation, knowns and unknowns about stellar UV variability, and how UV-SCOPE would fulfill our community’s UV needs.