Detection Feasibility of H${}_2$ in Ultra-hot Jupiter Atmospheres

Abstract

Ultra-hot Jupiters (UHJs) have recently been the focus of several atmospheric studies due to their extreme properties. While molecular hydrogen (H${}_2$) plays a key role in UHJ atmospheres, it has not been directly detected on an exoplanet. To determine the feasibility of H${}_2$ detection via transmission spectroscopy of the Lyman and Werner bands, we modeled UHJ atmospheres with H${}_2$ rotational temperatures varying from 2000 K to 4000 K orbiting A-type stars ranging from $T_{eff}$ = 8,500 K to $T_{eff}$ = 10,300 K. We present simulated transmission spectra for each planet-star temperature combination while adding Poisson noise varying in magnitude from 0.5% to 2.0%. Finally, we cross-correlated the spectra with expected atmospheric H${}_2$ absorption templates for each temperature combination. Our results suggest that H${}_2$ detection with current facilities, namely the Hubble Space Telescope, is not possible. However, direct atmospheric transmission spectroscopy of H${}_2$ may be viable with future UV-capable flagship missions.