Astronomers have achieved a groundbreaking feat by creating the first three-dimensional map of an exoplanet’s atmosphere, revealing distinct temperature zones, including areas so hot that water vapor disintegrates. This pioneering study, published in Nature Astronomy on October 28, 2025, was led by researchers from the University of Maryland and Cornell University.
The team focused on WASP-18b, a colossal gas giant located 400 light-years from Earth, classified as an “ultra-hot Jupiter.” By employing a novel technique known as 3D eclipse mapping, or spectroscopic eclipse mapping, they charted temperatures across the planet for the first time in three dimensions. This innovative approach builds upon a previous 2D map released in 2023, utilizing data from NASA’s James Webb Space Telescope (JWST).
Revolutionary Mapping Technique
“This technique is really the only one that can probe all three dimensions at once: latitude, longitude, and altitude,” said Megan Weiner Mansfield, the study’s co-lead author and 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.”
With this method, scientists can now explore atmospheric variations across numerous exoplanets observable by JWST, similar to how ground-based telescopes have documented Jupiter’s Great Red Spot and its banded clouds. Ryan Challener, a postdoctoral associate at Cornell University and co-lead author, explained, “Eclipse mapping allows us to image exoplanets that we can’t see directly, because their host stars are too bright.”
Challenges in Exoplanet Observation
Spotting exoplanets poses a significant challenge due to their dimness compared to their host stars, often contributing less than 1% of the total light. Eclipse mapping measures tiny variations in light as the planet moves behind its star, alternately hiding and revealing different regions. By analyzing these small brightness changes in multiple colors, scientists can reconstruct temperatures across various dimensions.
WASP-18b was an ideal candidate for this test, given its mass—about 10 times that of Jupiter—and its rapid 23-hour orbit, which results in temperatures nearing 5,000 degrees Fahrenheit. These characteristics provide a strong signal for the new mapping method.
Building the 3D Temperature Map
The team’s earlier 2D map utilized a single color of light, but the 3D version required reanalyzing JWST data from the Near-Infrared Imager and Slitless Spectrograph (NIRISS) across multiple wavelengths. Each color probes different layers of WASP-18b’s atmosphere, correlating to specific temperatures and altitudes. By combining these layers, researchers created a comprehensive three-dimensional temperature structure.
“If you build a map at a wavelength that water absorbs, you’ll see the water deck in the atmosphere, whereas a wavelength that water does not absorb will probe deeper,” Challener explained. “If you put those together, you can get a 3D map of the temperatures in this atmosphere.”
Discoveries on WASP-18b
The 3D analysis revealed spectroscopically distinct zones on the planet’s permanent dayside, which always faces the star due to tidal locking. A circular hot spot marks where the star’s light strikes most directly, with winds appearing too weak to distribute the heat effectively. A cooler ring surrounds this hot center near the planet’s limb, and measurements indicate reduced water vapor within the hot spot compared to the planet’s average.
“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 noted. “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.”
Future Implications and Research
Additional JWST observations could enhance the spatial detail of future 3D eclipse maps. Weiner Mansfield highlighted that this method opens new avenues for studying many “hot Jupiters,” which number in the hundreds among the more than 6,000 confirmed exoplanets. She also plans to apply 3D eclipse mapping to smaller, rocky worlds beyond gas giants like WASP-18b.
“It’s very exciting to finally have the tools to see and map out the temperatures of a different planet in this much detail. It’s set us up to possibly use the technique on other types of exoplanets,” Mansfield said. “For example, if a planet doesn’t have an atmosphere, we can still use the technique to map the temperature of the surface itself to possibly understand its composition.”
This research was supported by the James Webb Space Telescope’s Transiting Exoplanet Community Early Release Science Program, marking a significant advancement in the field of exoplanetary studies.
