For the first time, scientists have successfully created a detailed, three-dimensional map of an exoplanet’s atmosphere, offering unprecedented insights into distant worlds. This breakthrough, achieved using data from the James Webb Space Telescope (JWST) and a sophisticated technique called eclipse mapping, reveals distinct temperature zones within the atmosphere of WASP-18b, a gas giant located approximately 400 light-years from Earth. The new technique holds immense promise for charting temperature variations and cloud structures on other exoplanets in the future.
Understanding Eclipse Mapping: A Novel Approach
How it Works
Eclipse mapping allows astronomers to image exoplanets that are otherwise invisible due to the overwhelming brightness of their host stars. The technique capitalizes on the natural phenomenon where a planet passes behind its star, progressively obscuring the light it reflects. By meticulously measuring how the light from the exoplanet changes as it disappears and reappears, scientists can determine temperature variations at different altitudes and regions of the atmosphere. This is “extraordinarily challenging,” according to Ryan Challener, a researcher at Cornell University and co-author of the study published in Nature Astronomy.
Building on Previous Work: From 2D to 3D
Previously, scientists had created a two-dimensional temperature map of WASP-18b. The new study significantly expands upon this by leveraging JWST’s capabilities and utilizing different wavelengths of light to create a much more detailed 3D representation. By selectively observing wavelengths absorbed by substances like water, researchers could target specific atmospheric levels, effectively “peering” through the planet’s layers.
WASP-18b: A Unique Gas Giant
WASP-18b is a fascinating subject for study. This gas giant boasts approximately 10 times the mass of Jupiter, yet completes an orbit around its star in a remarkably short 23 hours. Due to tidal locking, one side of WASP-18b perpetually faces its star, experiencing constant sunlight, while the other side remains locked in darkness.
Key Discoveries About WASP-18b’s Atmosphere
The JWST observations revealed two distinct temperature zones on the day side of WASP-18b:
- A Central Hotspot: A circular region directly facing the star, receiving the most intense sunlight and displaying the highest temperatures.
- A Colder Ring: Extending outwards from the hotspot to the edge of the planet, indicating that atmospheric winds are not effectively redistributing heat across the entire surface.
Researchers also detected a lower concentration of water vapor within the hotspot compared to the planet’s overall atmospheric average. They theorize this could be due to temperatures so high that they are breaking down water molecules—a prediction previously supported by theory, now confirmed by observation.
“We think that’s evidence that the planet is so hot in this region that it’s starting to break down the water,” Challener said. “That had been predicted by theory, but it’s really exciting to actually see this with real observations.”
Looking Ahead: Future Research and Implications
The researchers acknowledge that further measurements with JWST can dramatically increase the resolution of WASP-18b’s atmospheric map. This would not only deepen our understanding of this particular exoplanet but also enable scientists to study the atmospheres of other gas giants, expanding our knowledge of planetary systems beyond our own. This breakthrough represents a significant leap forward in our ability to characterize exoplanets and search for potential signs of habitability on distant worlds.
