Webb Captures a Puffy Planet Shedding Its Atmosphere in Real Time

Astronomers have used NASA’s James Webb Space Telescope to watch a distant planet shedding its atmosphere into space, an event described in a study published in Nature Astronomy on December 1, 2025. The target is WASP-107b, a so-called super-puff: a gas giant about 200 light-years away that is unusually large for its mass, giving it a low, cotton-candy-like density.

Webb detected a sprawling cloud of escaping helium, called an exosphere, that extends nearly ten times the planet’s radius. Strikingly, this trail of gas is so vast that it begins passing in front of the host star about an hour and a half before the planet itself transits, a clear signature of an atmosphere streaming away into the surrounding space. Caroline Piaulet-Ghorayeb of the University of Chicago was among the co-authors of the work, which involved researchers from McGill University, the University of Geneva, and the University of Montreal.

“The target is WASP-107b, a so-called super-puff: a gas giant about 200 light-years away that is unusually large for its mass, giving it a low, cotton-candy-like density.”

Catching atmospheric escape in this kind of detail helps scientists understand how planets evolve over time. The gas a planet loses, and how fast it loses it, shapes what kind of world it ends up being, from a bloated gas giant to a stripped-down rocky core. WASP-107b’s puffy structure and the strong radiation from its star make it an ideal natural laboratory for studying processes that, over billions of years, may sculpt planets throughout the galaxy.

The researchers note that interpreting such measurements is intricate work; the size and shape of the escaping cloud depend on factors like stellar activity and the planet’s magnetic environment, which are still being modeled. But the result is a vivid example of how powerful modern instruments have become. Rather than inferring atmospheric loss indirectly, astronomers can now essentially watch it happen, deepening our picture of how the diverse worlds beyond our Solar System came to be.