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

Abstract

Transiting exoplanet atmospheric characterization is currently in a golden age as dozens of exoplanet atmospheres are being studied by NASA’s Hubble and James Webb Space Telescopes. This trend is expected to continue with NASA’s Pandora Smallsat and Roman Space Telescope and ESA’s Ariel mission (all expected to launch within this decade) and NASA’s 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 transmission/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 150 emission spectroscopy targets, we quantify the potential time lost to stale transit and eclipse ephemerides and find that hundreds of hours of space-based observing could be wasted given current uncertainties in orbital periods, transit epochs, and orbital eccentricities. 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 10 m telescope time. Based upon these findings, we provide a list of recommendations that would make community efforts for the preparation and interpretation of atmospheric characterization endeavors more effective and efficient. The strategies we recommend here can be used to support both current (e.g., Hubble Space Telescope and JWST) and future exoplanet atmosphere characterization missions (e.g., Pandora, Ariel, Roman, and the Habitable Worlds Observatory).