JWST Produces First 3D Atmospheric Map of Exoplanet WASP-18b, Revealing Thermal Architecture

Astronomers have achieved a significant milestone in astrophysics by generating the first three-dimensional topographical map of an exoplanet's atmosphere, utilizing the advanced capabilities of the James Webb Space Telescope (JWST). The focus of this pioneering work was WASP-18b, an ultra-hot Jupiter located roughly 400 light-years away, which possesses a mass nearly ten times that of Jupiter. This breakthrough transitions the study of distant planetary atmospheres from two-dimensional observations to comprehensive spatial models.

The scientific team employed a sophisticated technique known as 3D eclipse mapping. This method involves meticulously analyzing the subtle shifts in light wavelengths as WASP-18b passes behind its host star. By precisely measuring these variations, researchers were able to chart the thermal landscape across the planet's entirety, including its longitudes, latitudes, and different altitudes. This level of analytical detail offers a much deeper understanding of the atmospheric dynamics than previously possible with simpler observational methods.

The resulting thermal structure displayed a clear pattern: a prominent central hotspot on the planet's day-side, which was surrounded by a cooler outer band. This distinct thermal gradient indicates that the atmospheric circulation, driven by immense winds, is not strong enough to uniformly distribute the intense heat absorbed from the star. Furthermore, the investigation detected a localized deficit of water vapor specifically within this extremely hot central region when compared to the planet's overall composition.

This finding supports theoretical predictions, as the extreme temperatures in the hotspot are believed to cause the chemical breakdown, or dissociation, of water molecules. The research, co-led by Megan Wiener Mansfield of the University of Maryland and Jake Turner of Cornell University, provides tangible confirmation of complex atmospheric chemistry operating under such harsh conditions. The full details of this discovery were published in the journal Nature Astronomy on October 28, 2025.

This advancement represents a fundamental shift in how scientists can assess the complexity of worlds outside our solar system. The capacity to map thermal and chemical variations spatially offers an essential framework for evaluating the true nature of these distant spheres. The data gathered through eclipse mapping now allows scientists to move beyond basic transit depth measurements to examine the actual spatial distribution of energy and elements, promising to unlock secrets about the thermal regulation and chemical inventories across diverse exoplanetary systems.