This illustration shows what exoplanet WASP-39 b could look like, based on current understanding of the planet. WASP-39 b is a hot, puffy gas giant with a mass 0.28 times Jupiter (0.94 times Saturn) and a diameter 1.3 times greater than Jupiter, orbiting just 0.0486 astronomical units (4,500,000 miles) from its star. The star, WASP-39, is fractionally smaller and less massive than the Sun. Because it is so close to its star, WASP-39 b is very hot and is likely to be tidally locked, with one side facing the star at all times.
Data collected by Webb’s Near-Infrared Spectrograph (NIRSpec) show unambiguous evidence for carbon dioxide in the atmosphere, while previous observations from NASA’s Hubble and Spitzer space telescopes, as well as other telescopes, indicate the presence of water vapor, sodium, and potassium. The planet probably has clouds and some form of weather, but it may not have atmospheric bands like those of Jupiter and Saturn.
This illustration is based on indirect transit observations from Webb as well as other space and ground-based telescopes. Webb has not captured a direct image of this planet.
NASA’s James Webb Space Telescope has captured the first definitive detection of carbon dioxide in the atmosphere of a planet beyond our solar system. The result provides important insights into the composition and formation of the planet, and indicates that the telescope will be capable of measuring carbon dioxide on other exoplanets, including those that may potentially harbour life.
Identification of carbon dioxide in an exoplanet atmosphere, JWST Transiting Exoplanet Community Early Release Science Team