SiO and a super-stellar C/O ratio in the atmosphere of the giant exoplanet WASP-121 b
Abstract Refractory elements such as iron, magnesium and silicon can be detected in the atmospheres of ultrahot giant planets. 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 proved challenging, as the most prominent spectral features of associated atoms and molecules span a broad wavelength range. Here, using a single JWST observation of the ultrahot giant planet WASP-121 b, we report detections of H 2 O (5.5–13.5 σ ), CO (10.8–12.8 σ ) and SiO (5.7–6.2 σ ) in the planet’s dayside atmosphere and CH 4 (3.1–5.1 σ ) 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 CH 4 -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.
Authors
- Soichiro Hattori (ORCID: https://orcid.org/0000-0002-0842-863X)
- Jayesh Goyal (ORCID: https://orcid.org/0000-0002-8515-7204)
- Henrique Reggiani (ORCID: https://orcid.org/0000-0001-6533-6179)
- Eva-Maria Ahrer (ORCID: https://orcid.org/0000-0003-0973-8426)
- Duncan Christie (ORCID: https://orcid.org/0000-0002-4997-0847)
- Jiayin Dong (ORCID: https://orcid.org/0000-0002-3610-6953)
- Jake Taylor (ORCID: https://orcid.org/0000-0003-4844-9838)
- Daniel Foreman-Mackey (ORCID: https://orcid.org/0000-0002-9328-5652)
- T. M. Evans (ORCID: https://orcid.org/0000-0001-5442-1300)
- Joshua D. Lothringer (ORCID: https://orcid.org/0000-0003-3667-8633)
- Zafar Rustamkulov (ORCID: https://orcid.org/0000-0003-4408-0463)
- J. K. Barstow (ORCID: https://orcid.org/0000-0003-3726-5419)
- Nathan J. Mayne (ORCID: https://orcid.org/0000-0001-6707-4563)
- Tiffany Kataria (ORCID: https://orcid.org/0000-0003-3759-9080)
- Mark S. Marley (ORCID: https://orcid.org/0000-0002-5251-2943)
- David K. Sing (ORCID: https://orcid.org/0000-0001-6050-7645)
- Anjali A. A. Piette (ORCID: https://orcid.org/0000-0002-4487-5533)
- Cyril Gapp (ORCID: https://orcid.org/0009-0007-9356-8576)
Institutions
- Space Telescope Science Institute (US)
- Planetary Science Institute (US)
- Jet Propulsion Laboratory (US)
- American Museum of Natural History (US)
- Johns Hopkins University (US)
- University of Illinois Urbana-Champaign (US)
- National Institute of Science Education and Research (IN)
- Carnegie Institution for Science (US)
- The Open University (GB)
- University of Exeter (GB)
- University of Oxford (GB)
- Max Planck Institute for Astronomy (DE)
- Gemini South Observatory (CL)
- Flatiron Health (United States) (US)
- Flatiron Institute (US)
- Columbia University (US)
- University of Newcastle Australia (AU)
- University of Birmingham (GB)
Publication Details
- Journal
- Nature Astronomy
- Published
- 2025-06-02
- DOI
- https://doi.org/10.1038/s41550-025-02513-x
- Citations
- 10
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 11.55
Funders
- National Aeronautics and Space Administration
- Space Telescope Science Institute
- UK Research and Innovation
- Max-Planck-Gesellschaft
- Science and Technology Facilities Council