JWST Detects CO₂ in WASP-39b’s Atmosphere, Unlocking New Exoplanet Insights

Until recently, our understanding of exoplanet atmospheres was mainly limited to guesswork. But in a groundbreaking moment for space science, the James Webb Space Telescope has made a clear and direct detection of carbon dioxide (CO₂) in the atmosphere of WASP-39b—an exoplanet orbiting a Sun-like star 700 light-years away.

This is more than a first. It’s a proof of concept that JWST can chemically analyze exoplanet atmospheres with a level of precision unmatched by any previous instrument.

“This is a game-changing result,” said Dr. Knicole Colón, JWST deputy project scientist for exoplanet science at NASA.
(Source: NASA.gov)

A Deeper Look at WASP-39b

WASP-39b isn’t an Earth twin. It’s a hot gas giant roughly the size of Saturn, orbiting extremely close to its host star. But its thick, extended atmosphere made it a perfect candidate for transmission spectroscopy—analyzing starlight as it filters through the planet’s atmosphere.

Using the Near-Infrared Spectrograph (NIRSpec), JWST captured a distinct dip in the light spectrum corresponding to the absorption of carbon dioxide at 4.3 microns. This dip isn’t subtle—it’s a definitive fingerprint, leaving no ambiguity about CO₂’s presence.

Why It Matters for the Bigger Picture

While WASP-39b itself may not support life, this detection confirms that JWST can identify key ingredients of habitability in future, Earth-like targets.

It also provides insights into the formation history of WASP-39 b. The levels of carbon and oxygen suggest it likely formed farther from its star and migrated inward—evidence of dynamic planetary systems that challenge solar system-centric thinking.

And just as important: the precision of the reading sets the stage for detecting other potential biosignatures, such as water vapor, methane, or even oxygen, in rocky planets yet to be studied.

The Gateway to Exoplanet Chemistry Has Opened

This milestone solidifies JWST’s role not just as a telescope, but as a planetary chemist in space. It opens a new era in which we won’t just spot exoplanets—we’ll know what their skies are made of.

The following targets include TRAPPIST-1 system planets and other Earth-size worlds. And if carbon dioxide were this easy to find, more complex molecules may not be far behind.

The future’s unfolding—and we’re decoding it one trend at a time.
— Zane