The Webb Telescope collects the first atmospheric data from an exoplanet

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The James Webb Space Telescope has been in space for less than a year, but it’s already racked up an impressive list of firsts, from capturing the bones of another galaxy to detecting for the first time what may be some of the oldest galaxies in the universe. Now, Webb is making history again by collecting a complete chemical profile from the atmosphere of a distant exoplanet. New data released by multiple international teams across five studies (1,2,3,4,5) make WASP-39 b perhaps the best-studied planet outside our Solar System.

WASP-39 b orbits a Sun-like star about 700 light-years from Earth, but orbits it very closely. The exoplanet, which is roughly the size of Saturn, is eight times closer to our star than Mercury. The exoplanet was originally discovered using transit photometry, which analyzes small dips in light for evidence that an exoplanet has passed in front of a star. This method is most useful to us for detecting exoplanets, but it only works when the plane of the orbit passes in front of the star from our point of view.

By the same token, Webb could see WASP-39 b transiting the star to collect data from its atmosphere. As WASP-39 hits the planet with radiation, some of that energy is absorbed by molecules in the gas giant’s atmosphere. In this way, it is possible to get information on chemical processes at work, and some remarkable things are going on. For example, WASP-39 b is now the first exoplanet to have sulfur dioxide in its atmosphere. This production of these molecules is driven by high-energy light from the star and, given its location, is abundant in WASP-39 b. This is the first confirmation of photochemistry in an exoplanet.

Data from the study (three of which have been published in Nature, and two are still pending) also showed the presence of molecules such as carbon monoxide and carbon dioxide, confirming previous Web observations. Also contains sodium, potassium and lots of water vapor. Again, the latter confirms some previous ground and space-based observations. Knowing all these details helps scientists speculate on WASP-39 b’s composition, including how WASP-39 became so massive by devouring smaller planets inside the system—a possible conclusion based on its high sulfur-to-hydrogen ratio. The high oxygen content also suggests that WASP-39 b formed far from its host star before migrating inward.

This is just a hint of what the James Webb Space Telescope can do. Its ability to detect exoplanet atmospheres is turning out to be more powerful than astronomers expected. Turning to smaller, rocky planets like the Trappist-1 system, Webb could make even more incredible discoveries.

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