JWST builds the first chemical profile of an exoplanet atmosphere

The James Webb Space Telescope continues to open the world to new science. This time it is the first molecular and chemical profile of an exoplanet’s atmosphere, with signs of active photochemical reactions.

As part of the complete chemical profile of exoplanet Wasp 39b – where earlier this summer Webb found clear evidence of carbon dioxide in an exoplanet atmosphere – NASA said the telescope has captured more CO2as well as carbon monoxide, sodium, potassium and water vapour.

Sulfur dioxide (SO2) was also detected, which Oxford University researcher Shang-Min Tsai says is concrete evidence of photochemistry – chemical reactions initiated by light hitting a planet’s atmosphere. The Earth’s ozone layer was formed by photochemistry, for example.

“I see this as a really promising prospect for advancing our understanding of exoplanet atmospheres,” Tsai said.

Like when it detected CO2 in Wasp 39b’s atmosphere, the JWST relied on the planet’s transit around its star and how the chemicals in its atmosphere affected the wavelengths of light detected by the telescope. When light strikes various elements, they reflect different wavelengths, which the JWST can detect with pinpoint accuracy.

Three of Webb’s Four scientific instruments were used to build the atmospheric profile of Wasp 39b: the near-infrared and slitless image spectrograph (NIRISS), the near-infrared camera (NIRCam) and the near-infrared spectrograph (NIRSpec), which was used in two configurations.


Complete atmospheric profile of Wasp 39b, as captured by the JWST

Why atmospheric profiles are important

Awesome: We know what’s in the atmosphere of a gas giant eight times closer to its star than Mercury is to the Sun. So?

For one thing, the list of chemicals in an atmosphere provides researchers with relationships between them, which NASA says is fundamental to determining planet formation. Kazumasa Ohno, an exoplanet researcher at the University of California, Santa Cruz who worked with the JWST data, said Wasp 39b’s chemical composition gives researchers some clues.

“The abundance of sulfur [relative to] the hydrogen indicated that the planet likely experienced a significant accretion of planetesimals,” Ohno said. “The data also indicates that oxygen is much more abundant than carbon in the atmosphere. This potentially indicates that WASP-39 b originally formed far from the central star.”

The discovery of photochemistry also led to an additional first, according to NASA, of “scientists applying computer models of photochemistry to data requiring a full explanation of this physics.”

It is this application that NASA says has resulted in improvements to its modeling capabilities that “will help develop the technological know-how to interpret potential signs of habitability” in other exoplanets.

University of Bristol astrophysicist Hannah Wakeford said the Webb team predicted how well the observatory would perform, “but it was more accurate, more diverse and more beautiful than I actually thought”.

With a long, hard look at Wasp 39b out of the way and Webb’s instruments performing above expectations, NASA is ready for further exoplanet investigations. He can start looking at rockier worlds, like those of the TRAPPIST-1 system – many of which are in the star’s habitable zone.

Laura Flagg, a researcher at Cornell University and a member of the international Webb team, said the future looks bright for the JWST. “We’re going to be able to get a big picture of the atmospheres of exoplanets… It’s incredibly exciting to know that everything is going to be rewritten.” ®

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