Science / Space

A planet out of shape: astronomers measure an exoplanet atmosphere in 3D

Using a new method on JWST data, teams at Cornell and Bristol found the hot Jupiter WASP-17b has one side of its atmosphere puffed out by heat and day side winds. It is the first real shape measurement of its kind, and a benchmark for 6,000 known worlds.

Bristol, England · October 19, 2026

Exoplanet science usually deals in shadows and spectra, which makes this result unusual: a shape. Astronomers have measured the real shape of a planet's atmosphere for the first time, and it is not a neat circle. The planet is WASP-17b, a hot Jupiter 1,300 light years away, and one side of its atmosphere is puffed out, stretched by heat and by winds blowing off its permanent day side.

The method is the clever part. The teams at Cornell University and the University of Bristol used a technique called transmission strings on data from the James Webb Space Telescope, reading how the planet's atmosphere filters starlight as it crosses its sun. The work, published in Nature Astronomy and announced by the University of Bristol on October 14, turns that filtered light into a structure rather than a single averaged reading.

WASP-17b is an extreme test case, which is why it works as a demonstration. Hot Jupiters are locked facing their stars, so one hemisphere bakes while the other sits in permanent night, and the atmosphere is constantly being pushed from the hot side to the cold one. A puffed out limb is what that physics looks like when you can finally measure it instead of modelling it.

The value now is as a benchmark. More than 6,000 exoplanets have been confirmed, and most of what we know about their atmospheres comes from methods that flatten them into a ring of uniform depth. A technique that can show where an atmosphere is thick and where it is thin gives every future JWST observation a better question to ask. The catalogue of known worlds is large. The catalogue of worlds we can actually picture just got its first honest entry.