An international group of researchers, including astronomers from the University of Geneva (UNIGE) and the National Centre of Competence in Research PlanetS, has detected enormous clouds of helium drifting away from the exoplanet WASP-107b. The team gathered these observations with the James Webb Space Telescope and analyzed them using modeling tools created at UNIGE. Their results, reported in Nature Astronomy, offer important insights into atmospheric escape, a process that plays a central role in how planets evolve and develop their observable features.
Planetary atmospheres do not always remain intact. Even Earth steadily loses a small amount of material to space, shedding a little more than 3 kg of gas every second (mainly hydrogen). This continual loss, known as “atmospheric escape,” is especially relevant for planets that orbit extremely close to their stars. The intense heat they experience can drive dramatic outflows of gas, making the phenomenon a key factor in the long-term transformation of such worlds.
Webb’s First Helium Detection on an Exoplanet
Using the James Webb Space Telescope, researchers from UNIGE and universities in McGill, Chicago, and Montreal observed broad streams of helium leaving WASP-107b. The planet lies more than 210 light-years from our solar system. This marks the first time JWST has detected this element on an exoplanet, enabling scientists to examine the escaping gases in much greater detail than before.
A Deeply Inflated Super-Puff World
WASP-107b, discovered in 2017, orbits its star at a distance far tighter than Mercury’s orbit around the Sun. Although it is similar in size to Jupiter, it contains only about one-tenth of Jupiter’s mass. This extremely low density places it within the “super-puff” category of planets, which are known for their large size and unusually light composition.
The escaping helium originates from the planet’s extended upper atmosphere, known as the “exosphere.” This cloud is so large that it begins dimming the star’s light even before the planet itself passes in front of it. “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,” says Yann Carteret, a doctoral student in the Department of Astronomy at the Faculty of Science of the University of Geneva and co-author of the study.
Chemical Signatures Reveal the Planet’s Past
Along with helium, researchers identified water and several chemical compounds (including carbon monoxide, carbon dioxide, and ammonia) in WASP-107b’s atmosphere. They also found no detectable methane, even though JWST is capable of identifying it. These results help scientists reconstruct the planet’s early history. Evidence suggests that WASP-107b originally formed far from its current location before migrating inward. This inward shift could explain both its swollen atmosphere and the significant gas loss observed today.
The findings serve as a key reference for understanding how distant worlds change over time. “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,” explains Vincent Bourrier, senior lecturer and research fellow in the Department of Astronomy at the UNIGE Faculty of Science and co-author of the study.
“On Earth, atmospheric escape is too weak to drastically influence our planet. But it would be responsible for the absence of water on our close neighbor, Venus. It is therefore essential to fully understand the mechanisms at work in this phenomenon, which could erode the atmosphere of certain rocky exoplanets,” he concludes.
