Stefan Pelletier (Observatoire de Geneve) -- Unveiling the Atmospheric Composition of Ultra-hot Giant Exoplanets

Measuring the atmospheric composition of exoplanets and relating this to planet formation is a long-standing goal of the planetary science community. However, this task requires inferring abundances for the major elements from which planets form - a notoriously difficult task. Even for Jupiter and Saturn, we only have a handful of measurements, mainly due to their freezing cold temperatures causing most elements to condense out of the atmosphere.

 

With temperatures exceeding 2000K, ultra-hot Jupiters offer a unique opportunity to directly measure the composition of giant planets. Specifically, rock-forming species that would otherwise be impossible to measure on colder planets are vaporized and accessible via remote sensing. This means that we can measure refractory-to-volatile abundance ratios on ultra-hot Jupiters which tell us the relative amounts of rocks and ices that are accreted when giant planets form - something that remains unknown even for the Jovian planets in our Solar System.

 

I will present my efforts in using high-resolution spectroscopy to measure abundances in ultra-hot Jupiters.  First using the MAROON-X spectrograph to measure the abundances of a plethora of refractory elements on the ultra-hot Jupiter WASP-76b.  Second, combining ESPRESSO and CRIRES+ to measure major volatile and refractory species to derive the ice-to-rock ratio on the ultra-hot Jupiter WASP-121b.  For this latter planet, we derive elemental abundance ratios such as Fe/H, Fe/C, and Fe/O, finding some of these to deviate from both stellar and solar compositions. I will then discuss the implications of how and where in the protoplanetary disc such a planet could have formed. Finally, I will discuss dayside observations of the even hotter giant planet WASP-189b using HARPS+NIRPS, finding that although present, titanium appears to be underabundant relative to iron, suggesting that some of it is still cold-trapped on the nightside.