JWST detected carbon dioxide in the atmosphere of the exoplanet WASP-39b.
WASP-39b is a hot, inflated gas giant orbiting a Sun-like star about 700 light-years away. Because the planet passes frequently in front of its star and has a very extended atmosphere, it is an excellent target for transmission spectroscopy. During a transit, JWST measures the small, wavelength-dependent amount of starlight filtered through the planet’s atmosphere.
In August 2022, NASA announced that JWST had found the first clear evidence of carbon dioxide in an atmosphere beyond the Solar System. The signal appeared in data from the Near-Infrared Spectrograph, or NIRSpec. The observation also provided evidence of water vapor and other atmospheric constituents, giving researchers clues about the planet’s chemical makeup and formation.
WASP-96b is the nearby answer that often causes confusion: it was linked to JWST’s first exoplanet transmission spectrum and water-vapor detection. WASP-39b is the landmark world for the telescope’s first clear exoplanetary carbon-dioxide detection.