A New Approach to Compiling Exoatmospheric Target Lists And Quantifying the Ground-Based Resources Needed to Vet Them

Transiting exoplanet atmospheric characterization is currently in a golden age as dozens of transit- ing exoplanet atmospheres are being studied by NASA’s Hubble and James Webb Space Telescopes. This trend is likely to continue for the foreseeable future with the 2025 launch of NASA’s Pandora smallsat, the 2029 launch of ESA’s Ariel mission, which includes a contribution from NASA’s CASE project, and eventually the Habitable Worlds Observatory, expected to launch in the early 2040s, all of which are centered around studying the atmospheres of exoplanets. Here we explore a new approach to constructing large scale exoatmospheric survey lists, which combines the use of traditional trans- mission/emission spectroscopy figures of merit with a focus on more-evenly sampling planets across a range of radii and equilibrium temperatures. After assembling a sample target list comprised of 750 transmission spectroscopy targets and 75 emission spectroscopy targets, we quantify the potential time lost to stale transit and eclipse ephemerides finding that hundreds of hours of space-based observing could be wasted given current uncertainties in orbital periods, transit epochs, and orbital eccentric- ity. We further estimate the amount of ground-based telescope time necessary to obtain sufficiently precise exoplanet masses and find that it exceeds 100 nights of 10m telescope time. Based upon these findings, we provide a list of recommendations that would make community efforts for preparation and interpretation of atmospheric characterization endeavors more effective and efficient. The strategies we recommend here, including the target lists we develop, can be used to support both current (e.g., HST and JWST) and future atmospheric spectroscopy missions (e.g., Pandora, Ariel, and the Habitable Worlds Observatory).