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

TL;DR

This study assesses the potential for detecting molecular hydrogen in ultra-hot Jupiter atmospheres using transmission spectroscopy, finding current instruments insufficient but future missions promising.

Contribution

It models H$_2$ detection feasibility in UHJ atmospheres across various temperatures and star types, providing a framework for future observational strategies.

Findings

Current HST capabilities are insufficient for H$_2$ detection.

Detection may be possible with future UV-capable space telescopes.

Simulated spectra help guide future observational efforts.

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.