A team of scientists using the James Webb Space Telescope has observed a giant cloud of helium gas escaping from the atmosphere of a distant exoplanet, WASP-107b. This marks the first time that such a dramatic atmospheric loss has been captured in real time, with the escaping gas stretching nearly 10 times the planet’s radius and preceding it along its orbital path.
The study, published on December 1 in Nature Astronomy, involved researchers from McGill University, the University of Chicago, Université de Genève, and Université de Montréal. The findings provide new insight into how planetary atmospheres evolve over time, especially for giant planets that may have formed far from their host stars before migrating inward where they are exposed to intense heat.
Using Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS), the team detected an extensive helium exosphere around WASP-107b. This exosphere passes in front of its star about 1.5 hours before the planet itself begins its transit. The research also confirmed previous indications that water is present on WASP-107b, with greater confidence than earlier measurements made by the Hubble Space Telescope.
These observations offer clues about how planets form and migrate within their solar systems. Study co-author Caroline Piaulet-Ghorayeb of the University of Chicago said: “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.” She added: “The presence of another planet, WASP-107c, much farther out than WASP-107b, could have played a role in this migration.”
Piaulet-Ghorayeb further explained: “We are seeing molecules at the top of the atmosphere that must come from very deep, where the gas is much hotter. This so-called ‘vertical mixing’ is a key factor in the formation of water clouds and regulation of weather patterns on Earth.”
The international collaboration included scientists from several institutions such as McGill (Trottier Space Institute), University of Geneva, University of Chicago, Université de Montréal (Trottier Institute for Research on Exoplanets), Cornell University and Johns Hopkins University.
Funding for this research was provided by organizations including the Canadian Space Agency, NSERC Vanier scholarship program, Trottier Family Foundation, Brinson Foundation, European Research Council, Swiss National Science Foundation and NASA.
Citation: “Continuous helium absorption from the leading and trailing tails of WASP-107 b.” Krishamurthy et al., Nature Astronomy, Dec. 1, 2025.