James Webb Space Telescope finds first evidence of CO2 in exoplanet atmosphere

This same tech could someday help us discover strange, new – and habitable – worlds

NASA is reporting another James Webb Space Telescope (JWST) first as the orbital observatory has found clear evidence for carbon dioxide in the atmosphere of an exoplanet.

According to NASA, prior observations of CO2-rich WASP-39b by the Hubble and Spitzer telescopes were able to detect water vapor, sodium, and potassium in the planet's atmosphere. Webb's instruments are far more sensitive, the space agency said, enabling it to measure planetary atmospheres at a precision that could eventually help scientists identify potentially habitable planets.

The discovery utilized JWST's Near-infrared Spectrograph (NIRSpec) to capture data on the brightness of the light passing through 39b's atmosphere as it orbits its star. Because different gasses absorb different wavelengths of light, the Webb team was able to look at changes in 39b's light absorption to determine what the atmosphere is made of.

Located some 700 light-years from Earth and orbiting its star at just an eighth of the distance between the Sun and Mercury, WASP-39b is an ideal target for this sort of observation, NASA said.

Orbiting so close to its star means 39b has a transit time of just over four days, meaning researchers can get quick results from transmission spectroscopy, the process used to find its atmospheric CO2 and other gasses.

Zafar Rustamkulov, a Johns Hopkins University graduate student and member of JWST's Transiting Exoplanet Community Early Release Science team, says the discovery marks the crossing of an important threshold in exoplanet sciences.

The team's research paper has been accepted for publication in Nature, and is available in preprint form.

What a CO2-laden exoplanet means

Webb's sensitivity enables it to see individual colors across the 3-5.5 micron range, a precision that has never been possible with previous exoplanet observations. WASP-39b is a gas giant with properties that make it an ideal early benchmark for Webb's capabilities, but looking at planets so abundant in atmospheric gasses isn't the end goal for researchers.

In one example, JWST research team member Mike Line of Arizona State University says that carbon dioxide molecules are great at acting as tracers of a planet's formation. 

"By measuring this carbon dioxide feature, we can determine how much solid versus how much gaseous material was used to form this gas giant planet," Line said, adding that in the coming decade JWST would be using the technique to look at a variety of exoplanets. 

"Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets,"  said UC Santa Cruz's Natalie Batalha, who heads the Webb team conducting spectrography on WASP-39b.

In other words, if we point JWST's NIRSpec at some closer, more easily observed planets, we could discover a whole host of surprises in their atmospheres. ®

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