Chalk up another first for JWST: Observations of an exoplanet have unambiguously detected the presence of carbon dioxide in its atmosphere , something that has never been done before. This will lead to a better understanding of how exoplanets form, and hints at the ability to detect atmospheric gases in smaller rocky worlds as well [ link to paper ]. The planet is called WASP-39b, which was discovered in 2011 with the Wide-angle Search for Planets program . This uses what are essentially digital cameras with telephoto lenses to look at large swaths of the sky that contain large numbers of stars, measuring their brightnesses over time. If we happen to see a planet’s orbit edge-on, then once per orbit it passes in front of the star, blocking a little bit of the star’s light. This is called a transit , and is the single most successful method we use to find these alien worlds.  The host star in this case, WASP-39 , lies in the constellation of Virgo about 700 light-years from us.…