Webb Telescope Detects Carbon Dioxide on a Far-Away Planet

Finding this greenhouse gas on other worlds could give scientists clues in the search for extraterrestrial life

An artist's rendering of an exoplanet with its star in the background
An artist's rendition of the exoplanet, called WASP-39b NASA, ESA, CSA, Joseph Olmsted (STScI)

Researchers announced last week that the James Webb Space Telescope has captured the first definitive evidence of carbon dioxide in the atmosphere of a planet outside of our solar system.

“It’s incontrovertible. It’s there. It’s definitely there,” Peter Gao, co-author of the study and a planetary scientist at the Carnegie Institution for Science, tells Science NewsLisa Grossman. “There have been hints of carbon dioxide in previous observations, but never confirmed to such an extent.”

The findings were posted on the preprint server arXiv and have been accepted for publication in the journal Nature, according to a press release.

The far-away world, dubbed WASP-39b, is an exoplanet, which means that it's outside our solar system—in this case, it’s 700 light-years away. It’s a hot gas giant roughly the same mass as Saturn with a diameter about 1.3 times that of Jupiter, according to the release.

This discovery may help scientists better understand how the exoplanet formed, writes Science's Daniel Clery. And while WASP-39b is not likely to host alien life, the finding also shows Webb could detect carbon dioxide in the atmospheres of smaller, rockier planets that are more like Earth, which could aid the search for life beyond our solar system, per Science News.

Webb is “ushering in this new era of the atmospheric science of exoplanets,” Nikku Madhusudhan, who studies exoplanets at the University of Cambridge in England and did not contribute to the new research, tells Science.

This exoplanet was first discovered in 2011, according to the New York TimesDennis Overbye. It orbits its sun from a distance one-eighth of that between our sun and Mercury, so it’s too hot to support Earth-like life, per the Times.

“This planet is not a hospitable place,” Eliza Kempton, co-author of the new study and an exoplanet astronomer at the University of Maryland, tells New Scientist's Leah Crane. “It’s like what you would get if you took Jupiter but moved it really close to the sun and baked it.”

The Webb telescope, which launched at the end of last year, has already made a bunch of discoveries, from capturing stunning images of Jupiter to finding the most distant galaxies ever seen. Last week, NASA also expressed interest in aiming the telescope at a newly discovered exoplanet 100 light-years away, which researchers say might have an ocean of liquid water.

Webb started capturing data from WASP-39b in July. Water vapor, sodium and potassium had previously been detected in the planet’s atmosphere, according to Science, and the Spitzer Space Telescope once observed a faint hint of carbon dioxide from it, according to Science News. But that wasn’t enough to convince many scientists of the presence of this greenhouse gas. “I would not have bet more than a beer, at most a six pack, on that weird tentative hint of carbon dioxide from Spitzer,” Nicolas Cowan, an astronomer at McGill University in Canada who wasn’t involved in the new research, tells Science News.

But Webb was able to capture stronger evidence. When WASP-39b passed in front of its star, the space telescope detected infrared starlight that had filtered through the planet’s atmosphere, per Science. Light with a wavelength of about 4.3 micrometers was absorbed more by the gases blanketing the exoplanet, which is a sign of carbon dioxide’s presence there, according to Science News. Cowan tells Science News that the Webb evidence “is rock solid.”

Scientists hope to use the space telescope to eventually study the atmospheres of planets that are similar to Earth and learn more about the potential for life in other parts of the universe, per New Scientist. In the future, detecting carbon dioxide in combination with other gases like methane might be a strong indicator that a planet hosts life, Jessie Christiansen, an astrophysicist at the NASA Exoplanet Science Institute who was not involved in the research, tells the publication.

“This is the first step towards characterizing the atmospheres of habitable planets,” Kempton tells New Scientist.