Population-Level Transiting Exoplanets Atmosphere Studies with Roman

The Nancy Grace Roman Space Telescope (Roman), launching no earlier than August 2026, promises to revolutionise our understanding of exoplanets. Among its key science initiatives is the Galactic Bulge Time Domain Survey (GBTDS), which is projected to detect around 100,000 transiting exoplanets. This wealth of data will be instrumental for demographic studies, but will also provide insights into exoplanet atmospheres across our Galaxy via multi-band observations of transits, secondary eclipses and phase curves. To prepare the community for this exciting — and imminent — new science opportunity, we use end-to-end simulations to model realistic exoplanet atmosphere signals and analyse their recovered yield from mock Roman GBTDS light curves. We find a predicted yield of over 1000 secondary eclipses and ~100 of chromatic transits over the survey’s 5-year duration. For secondary eclipses alone, this offers a tenfold increase to the total number of eclipses observed by Spitzer over its lifetime. Early population-level atmospheric studies on smaller samples, particularly with hot Jupiters, have hinted at potential trends (or a puzzling lack thereof), such as a dayside flux discontinuity at Teq~1700 K (Deming et al. 2023) or a diversity of clear-to-cloudy atmospheres (Sing et al. 2016). However, the ability to make robust statistical inferences has thus far been hampered by the lack of sufficient sample sizes. To this end, the sheer amount of secondary eclipse and chromatic transit data provided by Roman will open up the ability to test these trends — and probe new ones — across the Galactic exoplanet population. We present our analysis of the predicted atmosphere science yields for the GBTDS and discuss their implications for population-level exoplanet atmosphere studies in this new era of big data astronomy.