Detection of atmospheric species and dynamics in the bloated hot Jupiter WASP-172 b with ESPRESSO

Context. The population of strongly irradiated Jupiter-sized planets has no equivalent in the Solar System. It is characterised by strongly bloated atmospheres and large atmospheric scale heights. Recent space-based observations of SO₂ photochemistry have demonstrated the knowledge that can be gained about Earth's uniqueness from detailed atmospheric studies of these unusual planets.
Aims: Here we explore the atmosphere of WASP-172 b, a planet similar in terms of temperature and bloating to the recently studied HD 149026 b. We characterise the atmospheric composition and subsequently the atmospheric dynamics of this prime target.
Methods: We observed a particular transit of WASP-172 b in front of its host star with ESO's ESPRESSO spectrograph and analysed the spectra obtained before, during, and after transit.
Results: We detect the absorption of starlight by WASP-172 b's atmosphere by sodium (5.6σ) and hydrogen (19.5σ) and obtained a tentative detection of iron (4.1σ). We detect strong - yet varying - blueshifts, relative to the planetary rest frame, of all of these absorption features. This allows for a preliminary study of the atmospheric dynamics of WASP-172 b.
Conclusions: With only one transit, we were able to detect a wide variety of species that clearly track different atmospheric layers with possible jets. WASP-172 b is a prime follow-up target for a more in-depth characterisation with both ground- and space-based observatories. If the detection of Fe is confirmed, this may suggest that radius inflation is an important determinant for the detectability of Fe in hot Jupiters, as several non-detections of Fe have been published for planets that are hotter but less inflated than WASP-172 b.