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A distant world is actively losing its atmosphere, and the James Webb Space Telescope has captured this rare phenomenon in real time. The planet, WASP-107b, is shedding helium gas into space, forming a substantial, forward-facing cloud that trails ahead of the planet as it orbits its star. This unprecedented view comes from JWST observations, which show the escaping gas stretching nearly ten times the planet’s radius and moving in front of WASP-107b along its orbital path. The finding offers new clues about how intense stellar radiation can gradually strip away the atmospheres of large, low-density planets.
WASP-107b is classified as a “super-puff” exoplanet because its radius is comparable to Jupiter’s, yet it has a much smaller mass, resulting in an exceptionally low density. It lies much closer to its star than Mercury is to the Sun—about seven times nearer than Mercury’s distance—making its atmosphere particularly vulnerable to escape. The expelled helium forms an exosphere that appears to precede the planet by roughly 1.5 hours, a phenomenon scientists refer to as pre-transit helium absorption. This means the helium cloud dims the star’s light slightly before the planet itself begins its transit.
Using JWST’s Near Infrared Imager and Slitless Spectrograph, researchers detected the infrared signature of helium streaming ahead of the planet, effectively creating a mini-transit that is observable as a faint dip in starlight before the planet blocks the star. While atmospheric escape has been observed on other exoplanets, WASP-107b represents the first instance of watching such a process unfold in near real time with this level of detail.
The data also shed light on the planet’s history. In addition to helium, water vapor has been detected high in the atmosphere, while methane is notably absent. This combination suggests vigorous vertical mixing that brings hotter, methane-poor gas upward. Taken together with the extreme atmospheric loss, these clues support the idea that WASP-107b likely formed farther from its star and migrated inward, where intense heating began peeling away its outer layers.
Co-author Caroline Piaulet-Ghorayeb notes that the atmospheric oxygen level appears higher than expected for a planet in that close orbit. She also points to the presence of another planet, WASP-107c, farther out, as a possible influence on WASP-107b’s inward migration. This scenario could help explain how the planet reached its current position while undergoing rapid atmospheric loss.
This discovery offers a vivid glimpse into how planetary atmospheres evolve over time and how some worlds may be stripped down to rocky or icy cores. The results were published on December 1 in Nature Astronomy.
Author spotlight: Samantha Mathewson, Space.com contributor, joined as an intern in 2016 and holds a B.A. in Journalism and Environmental Science from the University of New Haven. Her work has appeared in Nature World News, and she enjoys travel and photography in her spare time.
Discussion prompt: What do you think—could WASP-107b’s fate be common among “super-puffs”, or is this planet’s rapid evaporation an exceptional case? Should future missions prioritize studying atmospheric escape in similar worlds to better understand planetary evolution, or focus on completely different exoplanetary processes? Share your thoughts in the comments.
