The James Webb Space Telescope (JWST) has captured a breathtaking 3D view of a scorching planet's atmosphere, revealing a world of extreme temperatures and atmospheric mysteries. This groundbreaking achievement marks the first-ever 3D map of an exoplanet's atmosphere, showcasing distinct temperature regions, including one so intense that water vapor disintegrates. The findings were published in Nature Astronomy on October 28, 2025.
Led by researchers at the University of Maryland and Cornell University, the study focuses on WASP-18b, a massive gas giant classified as an 'ultra-hot Jupiter' located 400 light-years from Earth. The team utilized a cutting-edge technique called 3D eclipse mapping, or spectroscopic eclipse mapping, to create this detailed temperature map. This method builds upon their previous 2D eclipse map, which was released in 2023 and utilized highly sensitive observations from the JWST.
The technique, as explained by Megan Weiner Mansfield, an assistant professor of astronomy at UMD, is a powerful tool that can simultaneously probe latitude, longitude, and altitude. This level of detail allows scientists to study celestial bodies with unprecedented precision.
With this approach, scientists can now begin mapping atmospheric differences across various exoplanets observable by the JWST, similar to how ground-based telescopes have documented Jupiter's Great Red Spot. Eclipse mapping enables the observation of exoplanets that are otherwise too dim to see directly due to their host stars' brightness.
Ryan Challener, a postdoctoral associate in Cornell University's Department of Astronomy, highlights the challenge of spotting exoplanets, as they often contribute less than 1% of the total light. Eclipse mapping measures these tiny variations in light as the planet moves behind its star, revealing different regions. By analyzing these brightness changes in multiple colors, scientists can reconstruct temperature maps across the planet's surface.
WASP-18b's unique properties make it an ideal candidate for this test. With a mass equivalent to 10 Jupiters, a 23-hour orbit, and temperatures reaching 5,000 degrees Fahrenheit, it provides a strong signal for the new mapping method.
The 3D analysis revealed distinct zones on the planet's permanent dayside, which always faces the star due to tidal locking. A circular hot spot, where the star's light strikes most directly, is surrounded by a cooler ring near the planet's limb. Measurements also showed reduced water vapor within the hot spot compared to the planet's average.
This discovery challenges previous assumptions, as Megan Weiner Mansfield explains that it's the first time they've observed a planet with both cooler regions containing water and hotter regions where water vapor breaks apart. This finding aligns with theoretical predictions, but witnessing it in real observations is truly exciting.
The team's future plans include sharpening the spatial detail in 3D eclipse maps with additional JWST observations. Megan Weiner Mansfield emphasizes the potential for studying 'hot Jupiters' and expanding the technique to smaller, rocky worlds beyond gas giants. She also envisions using the method to map the temperature of a planet's surface, even if it lacks an atmosphere.
This research, supported by the James Webb Space Telescope's Transiting Exoplanet Community Early Release Science Program, opens up new possibilities for understanding exoplanets and their diverse atmospheric characteristics.
