Using high-precision spectroscopic observations from the Near-Infrared Imaging and Slitless Spectrograph (NIRISS) on board the NASA/ESA/CSA James Webb Space Telescope, astronomers have detected helium gas escaping from WASP-107b, a super-Neptune exoplanet located about 212 light-years away in the constellation Virgo.
Exoplanet WASP-107b as imagined by an artist. Image credit: University of Geneva/NCCR PlanetS/Thibault Roger.
WASP-107 is a highly active K-type main sequence star located approximately 212 light-years away in the constellation Virgo.
First discovered in 2017. OSA-107b is one of the least dense exoplanets known, a type that astrophysicists have dubbed “super-laminated” or “sweet” planets.
The planet orbits very close to the star – more than 16 times closer than Earth to the Sun – once every 5.7 days.
It has one of the coldest atmospheres of any exoplanet discovered, although at 500 degrees Celsius (932 degrees Fahrenheit) it is still significantly hotter than Earth.
The high temperature is thought to be the result of tidal heating caused by the planet's slightly non-circular orbit, and may explain how WASP-107b could be so inflated without resorting to extreme theories about how it formed.
“Sometimes a planet's atmosphere escapes into space,” said University of Geneva astronomer Ian Carteret and his colleagues.
“This is the case with the Earth, which irreversibly loses just over 3 kg of matter (mostly hydrogen) every second.”
“This process, called atmospheric escape, is of particular interest to astronomers for studying exoplanets very close to their star, which, when heated to extreme temperatures, are susceptible to this phenomenon.”
Using data from Webb's NIRISS instrument, astronomers have detected a huge flux of helium in the exosphere of WASP-107b.
This cloud partially blocks the star's light before the planet passes in front of it.
“Our models of atmospheric escape confirm the presence of helium streams both ahead and behind the planet, extending in the direction of its orbital motion to nearly ten planetary radii,” Carteret said.
In addition to helium, 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 researchers, the planet formed far from its current orbit and then moved closer to its star, which explains its bloated atmosphere and loss of gas.
“On Earth, the atmospheric ejection is too weak to have a radical impact on our planet,” said University of Geneva astronomer Vincent Bourrier.
“But it would be responsible for the lack of water on our close neighbor, Venus.”
“It is therefore important to fully understand the mechanisms at work in this phenomenon, which could destroy the atmospheres of some rocky exoplanets.”
conclusions appear in the magazine Nature Astronomy.
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V. Krishnamurti etc.. Continuous uptake of helium from both the front and tail of WASP-107b. Nat Astron, published online December 1, 2025; doi: 10.1038/s41550-025-02710-8
