A group of scientists using the James Webb Space Telescope have observed a giant cloud of helium gas evaporating from a distant giant planet.
While helium escape has been observed before, this is the first time the telescope has witnessed a planet’s atmosphere evaporating so violently that the escaping gas, stretching nearly 10 times the planet’s radius, actually precedes the planet along its path.
The findings offer researchers new insight into how planetary atmospheres evolve, particularly on giant planets that likely formed farther from their stars and later migrated inward, where intense heat can strip away their gases.
Studying these processes helps scientists better understand how planets evolve and change over time—a puzzle that is especially interesting as we seek to narrow the search for habitable planets.
The study, by researchers from McGill University, the University of Chicago, the Université de Genève and the Université de Montréal, was published Dec. 1 in Nature Astronomy.
A sprawling helium cloud
The new study focuses on WASP-107b, a giant planet located about 200 light-years away. This gas giant is classified as a 'super-puff'—a planet with an unusually large radius relative to its low mass.
Using the Webb telescope’s powerful Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument, the team detected a sprawling helium cloud known as an exosphere. This exosphere stretches nearly 10 times the radius of the planet and passes in front of the star 1.5 hours before the planet’s passage, or 'transit,' begins.
The researchers also reaffirmed that there appears to be water present on the planet, with stronger confidence than the previous Hubble Space Telescope measurements.
The detections provide clues about the planet’s formation and migration history.
Scientists would like to know much more about how planets form, especially as we seek habitable planets. For example, Earth’s atmosphere is key to keeping life safe on Earth, so scientists would like to understand the ingredients that lead to stable atmospheres on planets.
The evidence for WASP-107b suggests that the planet formed far from its current orbit and only recently moved closer to its star, which could explain its puffy, escaping atmosphere.
“We find that the amount of oxygen in the atmosphere of WASP-107 b is larger than what we would expect if it formed on its current close-in orbit,” said study co-author Caroline Piaulet-Ghorayeb of the University of Chicago. “The presence of another planet, WASP-107c, much farther out than WASP-107b, could have played a role in this migration.”
Piaulet-Ghorayeb also explained that the results indicate the planet’s atmosphere is undergoing significant stirring.
“We are seeing molecules at the top of the atmosphere that must come from very deep, where the gas is much hotter,” she said. “This so-called “vertical mixing” is a key factor in the formation of water clouds and regulation of weather patterns on Earth.”
The research was conducted by an international collaboration including scientists from McGill (Trottier Space Institute), the University of Geneva, the University of Chicago, Université de Montréal (Trottier Institute for Research on Exoplanets), Cornell and Johns Hopkins.
Citation: “Continuous helium absorption from the leading and trailing tails of WASP-107 b.” Krishamurthy et al., Nature Astronomy, Dec. 1, 2025.
Funding: Canadian Space Agency, NSERC Vanier scholarship, Trottier Family Foundation, Brinson Foundation, European Research Council, Swiss National Science Foundation, NASA.
—Adapted from a news release published by McGill University.
