For the first time, scientists have mapped a planet outside our solar system in three dimensions, revealing extreme temperature zones and shattered water vapour. The findings, published on October 28, 2025, in Nature Astronomy, show a new way to study alien worlds.
What did scientists discover about WASP-18b?
A team from the University of Maryland and Cornell University developed the first three-dimensional temperature map of WASP-18b, a gas giant orbiting a star about 400 light years away. The planet, nearly ten times heavier than Jupiter, completes its orbit in just 23 hours. With surface temperatures near 5,000 degrees Fahrenheit, it offered a perfect case for testing this new method.
The researchers used NASA’s James Webb Space Telescope to capture data and applied a process known as 3D eclipse mapping, or spectroscopic eclipse mapping. This method measures tiny changes in light as the planet moves behind its star, allowing scientists to link those shifts to specific regions of its atmosphere.
How does this mapping technique work?
The 3D eclipse mapping technique lets scientists visualise exoplanets that cannot be seen directly due to their bright host stars. By studying the light from different wavelengths, researchers can trace temperature and altitude variations within the planet’s atmosphere.
“If you build a map at a wavelength that water absorbs, you’ll see the water deck. But if the wavelength doesn’t absorb water, you’ll see deeper layers,” explained co-lead author Ryan Challener from Cornell University. “By combining these, we get a full 3D temperature map.”
What did the 3D map reveal?
The map showed distinct temperature regions on the planet’s dayside, which always faces its star. There is a circular “hot spot” receiving direct starlight, surrounded by cooler zones near the edges. The team also detected less water vapour in the hottest parts, suggesting extreme heat breaks water apart into its elements.
“This is the first time we’ve seen such contrast within one planet’s atmosphere,” said co-lead author Megan Weiner Mansfield of the University of Maryland. “Cooler regions retain water, while hotter ones lose it. It’s fascinating to see theory confirmed by real data.”
What’s next for exoplanet mapping?
The researchers believe more James Webb observations will sharpen these maps and may soon extend to other exoplanets. They hope the same method could be used to study smaller, rocky worlds too.
“It’s exciting to map temperatures on another planet with such precision,” Weiner Mansfield added. “If a planet lacks an atmosphere, we can still map its surface temperature and understand what it’s made of. We’re only beginning to see what’s possible.”
This pioneering 3D view of WASP-18b marks a major step in exploring exoplanets in unprecedented detail and understanding the climates of worlds beyond our own.
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