Refractory elements such as iron, magnesium, and silicon can be detected in ultrahot
giant planet atmospheres. This provides an opportunity to quantify the amount of
refractory material accreted during formation, along with volatile gases and ices.
However, simultaneous detections of refractories and volatiles have proven challenging,
due ...
Refractory elements such as iron, magnesium, and silicon can be detected in ultrahot
giant planet atmospheres. This provides an opportunity to quantify the amount of
refractory material accreted during formation, along with volatile gases and ices.
However, simultaneous detections of refractories and volatiles have proven challenging,
due to the most prominent spectral features of associated atoms and molecules
spanning a broad wavelength range. Here, using a single JWST observation of the
ultrahot giant planet WASP-121b, we report detections of H2O (5.5-13.5σ), CO (10.8-
12.8σ), and SiO (5.7-6.2σ) in the planet’s dayside atmosphere, and CH4 (3.1-5.1σ) in the
nightside atmosphere. We measure super-stellar values for the atmospheric C/H, O/H,
Si/H, and C/O ratios, which point to the joint importance of pebbles and planetesimals in
giant planet formation. The CH4-rich nightside composition is also indicative of
dynamical processes, such as strong vertical mixing, having a profound influence on the
chemistry of ultrahot giant planets.
