2025-10-28 ミシガン大学
The exoplanet WASP-18b is so hot that water molecules are split apart on its “dayside” that always faces its nearby sun, according to new research using the JWST. Image credit: NASA/JPL-Caltech (K. Miller/IPAC)
＜関連情報＞
- https://news.umich.edu/now-in-3d-maps-begin-to-bring-exoplanets-into-focus/
- https://www.nature.com/articles/s41550-025-02666-9
JWST分光日食マップから得られた太陽系外惑星の水平および垂直の熱構造 Horizontal and vertical exoplanet thermal structure from a JWST spectroscopic eclipse map
Ryan C. Challener,Megan Weiner Mansfield,Patricio E. Cubillos,Anjali A. A. Piette,Louis-Philippe Coulombe,Hayley Beltz,Jasmina Blecic,Emily Rauscher,Jacob L. Bean,Björn Benneke,Eliza M.-R. Kempton,Joseph Harrington,Thaddeus D. Komacek,Vivien Parmentier,S. L. Casewell,Nicolas Iro,Luigi Mancini,Matthew C. Nixon,Michael Radica,Maria E. Steinrueck,Luis Welbanks,Natalie M. Batalha,Claudio Caceres,Ian J. M. Crossfield,… Xi Zhang
Nature Astronomy Published:DOI:https://doi.org/10.1038/s41550-025-02666-9
Abstract
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.
