Atmosphere of a young exoplanet - DS Tuc Ab

Vigneshwaran Krishnamurthy ( Université McGill )

Young planets are valuable test beds for studying atmospheric escape and evolution, particularly for sub-jovians. Young hot sub-jovians offer crucial insights into the origins of the Neptunian desert, i.e., runaway mass-loss due to photoevaporation vs high-e migration followed by tidal decay. In this study, we present high resolution spectroscopic observations of DS Tuc Ab, a 850 K Neptune-sized planet in a spin-aligned orbit around a G-dwarf star within the 45 Myr old Tucana-Horologium moving group and residing at the apex of the Neptunian desert. Observations were conducted utilizing the Near Infra-Red Planet Searcher (NIRPS) in conjunction with HARPS, both installed on ESO’s 3.6m telescope in Chile. With a high resolution of ~80,000 in both instruments, we could effectively resolve the helium I triplet lines and the hydrogen Paschen-beta line in the NIR spectrum using NIRPS, alongside hydrogen Balmer lines observed with HARPS. Our analysis reveals a positive detection of both hydrogen and helium in the upper atmosphere of DS Tuc Ab, marking it as the youngest planet with a confirmed detection of H and He. This study is pivotal, as close-in transiting Neptunes are rare, likely because they are not robust to atmospheric loss. Our findings reveal that DS Tuc Ab is actively undergoing evaporation, a process projected to persist for 10-100 Myr. By the time the host star’s XUV drops, the planet may have lost enough mass to be just below the Neptunian desert.