Horizontal and vertical exoplanet thermal structure from a JWST spectroscopic eclipse map
Highly irradiated giant exoplanets known 'ultrahot Jupiters' are anticipated to exhibit large variations of atmospheric temperature and chemistry as a function of longitude, latitude and altitude. Previous observations have hinted at these variations, but the existing data have been fundamentally restricted to probing hemisphere-integrated spectra, thereby providing only coarse information on atmospheric gradients. Here we present a spectroscopic eclipse map of an extrasolar planet, resolving the atmosphere in multiple dimensions simultaneously. We analyse a secondary eclipse of the ultrahot Jupiter WASP-18b observed with the Near Infrared Imager and Slitless Spectrograph instrument on the JWST. The mapping reveals weaker longitudinal temperature gradients than were predicted by theoretical models, indicating the importance of hydrogen dissociation and/or nightside clouds in shaping global thermal emission. In addition, we identify two thermally distinct regions of the planet's atmosphere: a 'hotspot' surrounding the substellar point and a 'ring' near the dayside limbs. The hotspot region shows a strongly inverted thermal structure due to the presence of optical absorbers and a water abundance marginally lower than the hemispheric average, in accordance with theoretical predictions. The ring region shows colder temperatures and poorly constrained chemical abundances. Similar future analyses will reveal the three-dimensional thermal, chemical and dynamical properties of a broad range of exoplanet atmospheres.
Authors
- Benjamin V. Rackham (ORCID: https://orcid.org/0000-0002-3627-1676)
- Louis-Philippe Coulombe (ORCID: https://orcid.org/0000-0002-2195-735X)
- Thaddeus D. Komacek (ORCID: https://orcid.org/0000-0002-9258-5311)
- Jasmina Blecic (ORCID: https://orcid.org/0000-0002-0769-9614)
- Ε. Πάλλη (ORCID: https://orcid.org/0000-0003-0987-1593)
- Kevin B. Stevenson (ORCID: https://orcid.org/0000-0002-7352-7941)
- S. L. Casewell
- Luis Welbanks (ORCID: https://orcid.org/0000-0003-0156-4564)
- Xianyu Tan (ORCID: https://orcid.org/0000-0003-2278-6932)
- Jean-Michel Désert (ORCID: https://orcid.org/0000-0002-0875-8401)
- C. Cáceres (ORCID: https://orcid.org/0000-0002-6617-3823)
- Michael Radica (ORCID: https://orcid.org/0000-0002-3328-1203)
- Jacob L. Bean (ORCID: https://orcid.org/0000-0003-4733-6532)
- Nikolay Nikolov (ORCID: https://orcid.org/0000-0002-6500-3574)
- Ryan C. Challener (ORCID: https://orcid.org/0000-0002-8211-6538)
- Maria E. Steinrueck (ORCID: https://orcid.org/0000-0001-8342-1895)
- Karan Molaverdikhani (ORCID: https://orcid.org/0000-0002-0502-0428)
- Jake D. Turner (ORCID: https://orcid.org/0000-0001-7836-1787)
- Eliza M.-R. Kempton (ORCID: https://orcid.org/0000-0002-1337-9051)
- Björn Benneke (ORCID: https://orcid.org/0000-0001-5578-1498)
- Matthew C. Nixon (ORCID: https://orcid.org/0000-0001-8236-5553)
- Patricio E. Cubillos (ORCID: https://orcid.org/0000-0002-1347-2600)
- Nicolas Iro (ORCID: https://orcid.org/0000-0003-2329-418X)
- Vivien Parmentier (ORCID: https://orcid.org/0000-0001-9521-6258)
- David K. Sing (ORCID: https://orcid.org/0000-0001-6050-7645)
- Natalie M. Batalha (ORCID: https://orcid.org/0000-0002-7030-9519)
- Megan Mansfield (ORCID: https://orcid.org/0000-0003-4241-7413)
- Anjali A. A. Piette (ORCID: https://orcid.org/0000-0002-4487-5533)
- Everett Schlawin (ORCID: https://orcid.org/0000-0001-8291-6490)
- Hayley Beltz (ORCID: https://orcid.org/0000-0002-6980-052X)
- Nicolas Crouzet (ORCID: https://orcid.org/0000-0001-7866-8738)
- Joseph Harrington (ORCID: https://orcid.org/0000-0002-8955-8531)
- Emily Rauscher (ORCID: https://orcid.org/0000-0003-3963-9672)
- Luigi Mancini (ORCID: https://orcid.org/0000-0002-9428-8732)
- Xi Zhang (ORCID: https://orcid.org/0000-0002-8706-6963)
- Ian J. M. Crossfield
Institutions
- University of Central Florida (US)
- University of Rome Tor Vergata (IT)
- New York University Abu Dhabi (AE)
- Centre National de la Recherche Scientifique (FR)
- Space Telescope Science Institute (US)
- Planetary Science Institute (US)
- University of Arizona (US)
- Austrian Academy of Sciences (AT)
- Johns Hopkins University (US)
- University of Kansas (US)
- University of Leicester (GB)
- University of California, Los Angeles (US)
- University of Groningen (NL)
- Shanghai Jiao Tong University (CN)
- University of California, Santa Cruz (US)
- Carnegie Institution for Science (US)
- Université Côte d'Azur (FR)
- Cornell University (US)
- University of Michigan (US)
- Johns Hopkins Medicine (US)
- Johns Hopkins University Applied Physics Laboratory (US)
- Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (DE)
- University of Chicago (US)
- Space Research Institute (AT)
- Excellence Cluster Origins (DE)
- Osservatorio Astrofisico di Torino (IT)
- Max Planck Institute for Astronomy (DE)
- Observatoire de la Côte d’Azur (FR)
- Instituto de Astrofísica de Canarias (ES)
- Institute of Natural Science (KP)
- Montreal Clinical Research Institute (CA)
- Arizona State University (US)
- Massachusetts Institute of Technology (US)
- University of Maryland, College Park (US)
- University of Chile (CL)
- Université de Montréal (CA)
- Ludwig-Maximilians-Universität München (DE)
- University of Amsterdam (NL)
Publication Details
- Journal
- Nature Astronomy
- Published
- 2025-10-28
- DOI
- https://doi.org/10.1038/s41550-025-02666-9
- Citations
- 1
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 1.15
Funders
- National Aeronautics and Space Administration
- Research Corporation for Science Advancement
- University of Michigan
- New York University Abu Dhabi
- Space Telescope Science Institute
- Austrian Science Fund