Using high-precision spectroscopic observations from the Near Infrared Imager and Slitless Spectrograph (NIRISS) onboard the NASA/ESA/CSA James Webb Space Telescope, astronomers detected helium gas escaping from WASP-107b, a super-Neptune exoplanet approximately 212 light-years away in the constellation of Virgo.
An artist’s impression of the exoplanet WASP-107b. Image credit: University of Geneva / NCCR PlanetS / Thibaut Roger.
WASP-107 is a highly active K-type main sequence star located about 212 light-years away in the constellation of Virgo.
First discovered in 2017, WASP-107b is one of the least dense exoplanets known — a type that astrophysicists have dubbed ‘super-puff’ or ‘cotton-candy’ planets.
The planet orbits very close to the star — over 16 times closer than the Earth is to the Sun — once every 5.7 days.
It has one of the coolest atmospheres of any of the exoplanets discovered, although at 500 degrees Celsius (932 degrees Fahrenheit) is still radically hotter that Earth.
The high temperature is thought to be a result of tidal heating caused by the planet’s slightly non-circular orbit, and can explain how WASP-107b can be so inflated without resorting to extreme theories of how it formed.
“Sometimes a planet’s atmosphere escapes into space,” said University of Geneva astronomer Yann Carteret and colleagues.
“This is the case for Earth, which irreversibly loses a little over 3 kg of matter (mainly hydrogen) every second.”
“This process, called atmospheric escape, is of particular interest to astronomers for the study of exoplanets located very close to their star, which, heated to extreme temperatures, are precisely subject to this phenomenon.”
Using data from Webb’s NIRISS instrument, the astronomers detected a vast helium flow in the exosphere of WASP-107b.
This cloud partially blocks the star’s light even before the planet 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,” Carteret said.
In addition to helium, the astronomers were able to confirm the presence of water and traces of chemical mixtures (including carbon monoxide, carbon dioxide, and ammonia) in the atmosphere of WASP-107b.
These are valuable clues for reconstructing the history of its formation and migration.
According to the researcjers, the planet formed far from its current orbit, then moved closer to its star, which would explain its bloated atmosphere and loss of gas.
“On Earth, atmospheric escape is too weak to drastically influence our planet,” said University of Geneva astronomer Vincent Bourrier.
“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.”
The findings appear in the journal Nature Astronomy.
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V. Krishnamurthy et al. Continuous helium absorption from both the leading and trailing tails of WASP-107b. Nat Astron, published online December 1, 2025; doi: 10.1038/s41550-025-02710-8
