Astronomers have created the first three-dimensional map of an exoplanet's atmosphere using NASA's James Webb Space Telescope. The map reveals temperature variations on WASP-18b, an ultra-hot Jupiter 400 light-years away. This breakthrough technique could extend to studying smaller, rocky planets.
Researchers from the University of Maryland and Cornell University led the study, published in Nature Astronomy on October 28, 2025. They applied 3D eclipse mapping, or spectroscopic eclipse mapping, to WASP-18b, a gas giant with the mass of 10 Jupiters. Orbiting its star every 23 hours, the planet reaches temperatures near 5,000 degrees Fahrenheit and is tidally locked, always showing one side to its star.
The technique builds on a 2D map from 2023, using data from JWST's Near-Infrared Imager and Slitless Spectrograph (NIRISS). By analyzing light variations across multiple wavelengths as the planet eclipses its star, the team reconstructed temperatures in latitude, longitude, and altitude. "This technique is really the only one that can probe all three dimensions at once: latitude, longitude and altitude," said co-lead author Megan Weiner Mansfield, an assistant professor of astronomy at the University of Maryland. "This gives us a higher level of detail than we've ever had to study these celestial bodies."
The 3D map shows a circular hot spot where starlight hits directly, surrounded by a cooler ring. Winds are too weak to distribute heat evenly, and the hot spot has reduced water vapor, where molecules break apart due to extreme heat. "We've seen this happen on a population level, where you can see a cooler planet that has water and then a hotter planet that doesn't have water," Weiner Mansfield explained. "But this is the first time we've seen this be broken across one planet instead. It's one atmosphere, but we see cooler regions that have water and hotter regions where the water's being broken apart."
Co-lead author Ryan Challener, a postdoctoral associate at Cornell University, noted, "Eclipse mapping allows us to image exoplanets that we can't see directly, because their host stars are too bright." The method measures light dips less than 1% as the planet transits, tying them to specific atmospheric layers. Supported by JWST's Transiting Exoplanet Community Early Release Science Program, future observations could refine maps for hundreds of hot Jupiters and potentially rocky worlds. Mansfield added that the tool could map surfaces without atmospheres to infer composition.