Astronomers have achieved an unprecedented breakthrough in the study of exoplanetary atmospheres by generating the first-ever three-dimensional thermal map of a planet outside our solar system. This groundbreaking research, recently published in Nature Astronomy on October 28, 2025, unveils a detailed, volumetric temperature profile of WASP-18b—a monstrous “ultra-hot Jupiter” situated approximately 400 light-years from Earth. This new 3D map elucidates distinct atmospheric temperature zones, including an intensely heated region where water vapor undergoes thermal dissociation, fundamentally altering our comprehension of exoplanet climates.
The revolutionary technique employed by the research team, co-led by experts from the University of Maryland and Cornell University, is known as 3D eclipse mapping or spectroscopic eclipse mapping. This method capitalizes on precise measurements of the planet’s light at different wavelengths as it is periodically eclipsed by its host star. Unlike previous two-dimensional mappings that offered surface brightness distributions in latitude and longitude, this approach integrates altitude as a third dimension by exploiting spectroscopic data, thereby rendering a comprehensive three-dimensional thermal and chemical portrait of the exoplanet’s atmosphere.
WASP-18b serves as an ideal subject for this investigative method due to its extreme physical properties. With a mass about ten times that of Jupiter and an orbital period of only 23 hours, the planet endures relentless stellar irradiation resulting in atmospheric temperatures soaring to nearly 5,000 degrees Fahrenheit (around 2,760 degrees Celsius). Such intense conditions generate a robust infrared emission signal, enabling the James Webb Space Telescope (JWST), specifically its Near-Infrared Imager and Slitless Spectrograph (NIRISS), to capture detailed spectral data across multiple wavelengths essential for constructing the 3D thermal map.
The essence of the technique lies in its spectral sensitivity to different atmospheric layers and constituents. For instance, wavelengths strongly absorbed by water vapor reveal regions where water molecules dominate, effectively tracing higher atmospheric altitudes. Conversely, wavelengths at which water absorption is minimal provide insight into deeper layers. By analyzing this spectral variance, scientists can interpolate thermal gradients vertically and horizontally across the atmosphere, creating an intricate three-dimensional representation. This enables the differentiation of temperature and chemical composition not only across the planetary surface but also throughout its gaseous envelope.
The data reveals a fascinating thermal dichotomy on WASP-18b’s dayside hemisphere, which is perpetually exposed to its star due to tidal locking. A conspicuous circular hotspot emerges where direct stellar irradiation is maximal, characterized by scorching temperatures and a notable depletion of water vapor. This suggests that the thermal energy in this hotspot is sufficient to dissociate water molecules, fundamentally changing local atmospheric chemistry. Surrounding this blistering core is a cooler ring, marking the atmospheric periphery visible from Earth, where water vapor remains more abundant and temperatures drop significantly.
This spatial heterogeneity provides compelling observational validation for theoretical models previously posited but never confirmed at such granular scales. The presence of water vapor depletion exclusively within the hotspot, contrasted with continuing water absorption in adjacent cooler regions, offers insights into the complex interplay between stellar radiation, atmospheric dynamics, and molecular chemistry under extreme conditions. These findings underscore the nuanced and dynamic nature of ultra-hot Jupiter atmospheres, revealing previously inaccessible details about their physical and chemical processes.
The implications of this study extend far beyond WASP-18b. By opening the door to 3D eclipse maps, this research equips astronomers with a powerful new tool to decipher atmospheric structures of numerous exoplanets observable by JWST. This leap in observational capability parallels historical advancements in Earth-based telescope studies of our own solar system’s giants, such as Jupiter’s Great Red Spot and banded cloud formations. Now, scientists can apply similar analytical frameworks to worlds light-years away, enriching our understanding of planetary atmospheres in diverse cosmic environments.
Detection of exoplanets suffers from the intrinsic challenge that these objects are generally billions of times fainter than their luminous host stars, which greatly complicates direct imaging endeavors. Eclipse mapping circumvents this limitation by meticulously monitoring the subtle flux variations as planets transit or pass behind their stars, effectively isolating the planet’s emitted or reflected light. The capacity to decode these faint signals into spatially resolved thermal maps marks a paradigm shift, as it enables not just detection but atmospheric characterization across multiple dimensions on distant worlds.
Beyond ultra-hot Jupiters, researchers are optimistic about extending 3D eclipse mapping to smaller, rocky exoplanets, including those lacking thick atmospheres. For these bodies, mapping techniques could elucidate surface temperature distributions, potentially informing us about their composition, geological activity, and habitability potential. WASP-18b’s relatively straightforward, tidally locked configuration laid a predictable foundation for method validation, but future JWST observations promise to reveal surprises among more complex planetary atmospheres, challenging existing models and expanding planetary science horizons.
The study’s success owes much to the exquisite sensitivity and spectral range of JWST’s NIRISS instrument. By reanalyzing data initially acquired for 2D mapping purposes but now interpreted across multiple wavelengths, the team achieved vertical atmospheric profiling enabling altitude differentiation. This methodological innovation demonstrates the enormous scientific return afforded by repurposing and enhancing existing observational datasets with cutting-edge computational models and atmospheric retrieval techniques. Such synergistic use of instrumentation and theory exemplifies the collaborative advances defining modern astrophysical research.
Ultimately, this pioneering 3D eclipse map represents a watershed moment in exoplanetary science, as it provides an unprecedented window into the atmospheric physics and chemistry of distant worlds. It not only confirms fundamental theoretical predictions—such as water vapor dissociation under extreme irradiation—but also helps refine atmospheric circulation models by clarifying the spatial extent and intensity of thermal hotspots and cooler peripheral zones. These refined models will be crucial for interpreting observations of exoplanets with an ever-increasing level of detail as future space missions and ground-based facilities enhance observational capabilities.
In the words of lead researchers Megan Weiner Mansfield and Ryan Challener, this breakthrough ushers in a transformative era wherein exoplanets, once mere points of data, become richly characterized worlds with complex thermal landscapes. This observational feat brings us closer than ever to understanding the physical nature of planets beyond our solar system on par with the detailed knowledge we possess about our own planetary neighbors. As JWST continues to deliver more high-precision data, we can anticipate a flood of discoveries that will fundamentally reshape exoplanetary atmospheres research for years to come.
The success of this research reflects the growing synergy between advanced space telescopes, innovative observational techniques, and sophisticated data analysis. As astronomers continue pushing the frontiers of exoplanet characterization, methods like 3D eclipse mapping offer unparalleled prospects to explore the diversity and complexity of planetary atmospheres, paving the way towards answering profound questions about planetary formation, evolution, and potential habitability in the cosmos.
Subject of Research: Exoplanet atmospheric characterization; 3D thermal mapping of ultra-hot Jupiter WASP-18b.
Article Title: Horizontal and Vertical Exoplanet Thermal Structure from a JWST Spectroscopic Eclipse Map.
News Publication Date: October 28, 2025.
Web References:
References:
- Mansfield, M.W., Challener, R., et al. (2025). Horizontal and Vertical Exoplanet Thermal Structure from a JWST Spectroscopic Eclipse Map. Nature Astronomy.
Image Credits: NASA/GSFC
Keywords: Exoplanetary science, Exoplanets, Ultra-hot Jupiters, Spectroscopic eclipse mapping, Atmospheric chemistry, Atmospheric temperature mapping, James Webb Space Telescope, WASP-18b, Atmospheric dissociation, Infrared spectroscopy, Planetary atmospheres, Space exploration.
