James Webb telescope spots strange 'super-puff' planet chasing its own atmosphere through space

An illustration of a distant planet shrouded in purple hydrogen gas — An illustration of exoplanet WASP-107b. The planet's escaping hydrogen atmosphere measures five time the radius of the planet itself, new JWST observations hint. (Image credit: University of Geneva/NCCR PlanetS/Thibaut Roger)

A "super-puff" exoplanet is leaking a lot of helium into space, new observations show — and may be in the process of losing a lot of its atmosphere.

A large plume of helium gas was spotted evaporating from the giant planet, known as WASP-107b, according to research based on observations from the James Webb Space Telescope (JWST).

Planet puff-ball

WASP-107b was discovered in 2017 near a star about 210 light-years from Earth. (For comparison, the closest planets to us are about 4 light-years away.) WASP-107b is almost the same size as Jupiter, at 94% of the gas giant's diameter, but its mass is just 12% that of Jupiter. This extremely low density and large size place WASP-107b in the "super-puff" category of exoplanets.

Aside from its unusual density, WASP-107b is in an interesting spot: It is seven times closer to its star than Mercury is to the sun. In Earth's neighborhood, by contrast, rocky planets are closer to the sun and gas giants like Jupiter are farther away. That means scientists must come up with models to explain that difference.

They think WASP-107b, like Jupiter and Saturn, formed much farther from its star but something in the system — possibly another planet — forced WASP-107b to migrate closer to its star over time.

"WASP-107c, much farther out than WASP-107b, could have played a role in this migration," study co-author Caroline Piaulet-Ghorayeb, an exoplanet researcher now at the University of Chicago who completed her Ph.D. at the University of Montreal in 2024, said in the statement.

An illustration of a planet transiting a star — Another illustration of WASP-107b whipping past its star. (Image credit: Angel P. Geego)

Once the planet got close enough to its star, the extreme heat of its new orbit began gutting the exoplanet's gassy atmosphere, the researchers explained. The new JWST observations confirmed the extent of the damage: The powerful telescope spotted the helium cloud of the exoplanet's atmosphere passing in front of the system's parent star about 1.5 hours before WASP-107b itself.

The researchers spotted several elements in WASP-107b's atmosphere that reveal more clues about the planet's complicated history. For example, there was more oxygen in the planet's atmosphere than would be predicted if it had formed close to its star, which provides more evidence that its migration was relatively recent.

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JWST also found water in the planet's atmosphere — confirming previous observations from the Hubble Space Telescope — alongside traces of carbon monoxide, carbon dioxide and ammonia. But methane, which was predicted to be part of the planet's atmosphere due to its chemistry, was curiously absent.

Because JWST's instruments are sensitive enough to detect methane from afar, the researchers suggest other gases poor in methane must have instead been drawn up from deep in the planet's atmosphere due to "vigorous vertical mixing" driven by the heat of the star, Piaulet-Ghorayeb added.

While planets like Earth also have some atmospheric loss, it is not this extreme. Studying worlds like WASP-107b could help us understand how atmospheric escape works on planets like Venus, which lost water over the eons, the research team said in a statement from the University of Geneva.

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Elizabeth Howell was staff reporter at Space.com between 2022 and 2024 and a regular contributor to Live Science and Space.com between 2012 and 2022. Elizabeth's reporting includes multiple exclusives with the White House, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?" (ECW Press, 2022) is co-written with astronaut Dave Williams.

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