Astronomers using the James Webb Space Telescope have observed vast helium clouds escaping from the super-puff exoplanet WASP-107b, marking the first such detection by the observatory. This finding reveals how intense stellar radiation strips gases from the planet's inflated atmosphere. The observations provide key insights into atmospheric escape and planetary evolution.
An international team, including researchers from the University of Geneva and the National Centre of Competence in Research PlanetS, used the James Webb Space Telescope to detect broad streams of helium drifting away from WASP-107b. Located over 210 light-years from Earth, this exoplanet orbits its star closer than Mercury does to the Sun. Despite its Jupiter-like size, WASP-107b has only about one-tenth of Jupiter's mass, classifying it as a super-puff with an unusually low density and extended atmosphere.
The helium originates from the planet's exosphere, forming clouds that extend nearly ten times the planet's radius and dim the star's light before the planet transits. "Our atmospheric escape models confirm the presence of helium flows, both ahead and behind the planet, extending in the direction of its orbital motion to nearly ten times the planet's radius," said Yann Carteret, a doctoral student at the University of Geneva and co-author of the study.
Analysis also revealed water, carbon monoxide, carbon dioxide, and ammonia in the atmosphere, but no detectable methane. These chemical signatures suggest WASP-107b formed far from its star before migrating inward, where scorching heat now drives significant gas loss. The results, published in Nature Astronomy, highlight atmospheric escape as a key process in planetary development.
Even Earth loses about 3 kg of gas per second to space, mostly hydrogen, though this rate is minimal compared to close-in exoplanets. "Observing and modeling atmospheric escape is a major research area at the UNIGE Department of Astronomy because it is thought to be responsible for some of the characteristics observed in the exoplanet population," explained Vincent Bourrier, a senior lecturer at the University of Geneva. This phenomenon may explain Venus's lack of water and could erode atmospheres on rocky exoplanets elsewhere.
