The James Webb Space Telescope has observed that the atmosphere of WASP-17b, a hot Jupiter located roughly 1,300 light-years from Earth, bulges outward asymmetrically on one side rather than forming a uniform sphere.
The discovery, published in Nature Astronomy, emerged from research jointly led by Cornell University and the University of Bristol using a technique called "transmission strings" or transit mapping. This method separates atmospheric measurements from different regions around a planet's limb, revealing variations that traditional approaches would average away.
The asymmetry occurs on WASP-17b's evening side, where powerful atmospheric winds transport heat away from the permanently illuminated hemisphere toward the dark side. This movement causes the atmosphere to expand farther outward on the cooler morning side, matching predictions from theoretical models.
Dr. Lili Alderson, lead author and Klarman Postdoctoral Fellow at Cornell, stated: "This is proof of concept that planets are in fact 3D objects, and that consistently, as they go around their star, what we predict should be happening is happening."
The transmission strings technique examines starlight passing through the outer edges of an exoplanet's atmosphere as it transits its host star. By analyzing that light from different angles, researchers determined atmospheric composition and how far it extends at different locations.
Dr. Hannah Wakeford of the University of Bristol added: "Planets are temperamental, their atmospheres complex and chaotic. The fact that all of these numbers came together and showed us this very structured, dynamical picture of this giant world over 1,000 light-years away was just really exciting."
The findings demonstrate how transmission strings could be applied to study atmospheres on thousands of other confirmed exoplanets, potentially enabling scientists to map weather patterns on distant worlds.