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‘First Clear Evidence’ of Carbon Dioxide in Exoplanet Atmosphere Found by Webb Telescope


NASA’s James Webb Space Telescope has captured the first clear evidence of carbon dioxide in the atmosphere of a planet outside our solar system.


NASA has announced that the James Webb Space Telescope (JWST)—an infrared observatory orbiting the Sun about 1 million miles from Earth, launched in December of last year—has captured “the first clear evidence for carbon dioxide in the atmosphere of a planet outside the solar system.” The space agency says the exoplanet—or planet outside our solar system—is 700 light-years away, and is a gas giant like Jupiter or Saturn.

Image: NASA, ESA, CSA, and J. Olmsted (STScI)

The distant exoplanet—dubbed WASP-39 b—exhibits “extreme puffiness” according to NASA, as it has a diameter that measures 1.3 times that of Jupiter’s, yet only has 25% of the planet’s mass. NASA also says the exoplanet orbits quite closely to its parent star—at a distance that equates to about 13% of that between the Sun and Mercury. Which means a full trip around its parent star takes WASP-39 b only four Earth-days.

As JWST’s twitter account notes in an explainer thread, space telescopes like NASA’s Hubble Space Telescope and the Spitzer Space Telescope had already detected the presence of water vapor, sodium, and potassium in WASP-39 b‘s atmosphere. Powerful telescopes like these are able to glean the molecular and elemental makeup of other planets’ atmospheres by studying the light that bounces off of them as different elements and molecules absorb and emit different types of light. Rayleigh scattering, or the absorption and re-emission of light off molecules in our atmosphere, for example, gives us our blue skies.

“We learn about exoplanet atmospheres by breaking their light into components and creating spectra,” NASA Webb writes in its explainer thread. “Think of a [light] spectrum as a barcode. Elements and molecules present have characteristic signatures in that ‘barcode'” that can be deciphered as being emitted by one type of element or molecule or another type.

While Hubble and Spitzer were able to pick up on light signatures of some elements or molecules in WASP-39 b‘s atmosphere, however, NASA notes it required “Webb’s extraordinary infrared sensitivity to reveal the signature of carbon dioxide.” (Incidentally, carbon dioxide’s relatively unique ability to absorb and re-emit infrared light is what makes it an effective heat-trapping greenhouse gas.)

An artist’s illustration of WASP-39 b. Image: NASA, ESA, CSA, and L. Hustak (STScI)

“As soon as the data appeared on my screen, the whopping carbon dioxide feature grabbed me,” Zafar Rustamkulov, a graduate student at Johns Hopkins University and member of the JWST Transiting Exoplanet Community Early Release Science team, which undertook this investigation, said in a NASA press release. “It was a special moment, crossing an important threshold in exoplanet sciences.”

“Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets,” Natalie Batalha of the University of California at Santa Cruz, who led the team behind the discovery, added in NASA’s release.

As for how astronomers knew WASP-39 b was there at all in the first place, the planet gave itself away by periodically dimming the light coming from its parent star—blocking the light from its star that we receive here on/near Earth as it orbited between its solar parent and our telescopes (see the top portion of the diagram at the top of this post). In the tweet immediately above Batalha walks us through how the starlight blocked by WASP-39 b is especially blocked by light with the wavelength signature associated with carbon dioxide. Batalha also shows how Webb’s observation of the planet’s infrared light helped to increase greatly the resolution of that CO2 signature.

Looking forward, NASA echoes Batalha’s excitement, noting this discovery offers evidence that Webb may be able to detect and measure carbon dioxide in thinner atmospheres of smaller rocky planets. I.e. planets more like our own, where carbon dioxide allows life to thrive.


Feature image: NASA, ESA, CSA, and J. Olmsted (STScI)

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