sciencehabit quotes a report from Science magazine: Astronomers have found carbon dioxide (CO2) in the atmosphere of a Saturn-sized planet 700 light-years away – the first unambiguous detection of the gas on a planet outside the Solar System. The discovery, made by the James Webb Space Telescope, provides clues about how the planet formed. The result also shows how quickly Webb can identify the flow of other gases, such as methane and ammonia, that could indicate a planet’s potential habitability. […] For the first exoplanet observations, astronomers targeted the hot gas giant WASP-39b, which orbits its star every 4 days in an orbit much tighter than Mercury’s. The first data was received on July 10, and the team started working on it a few days later. Even in the raw data, based on a single pass through the star, the CO2 spectral dip “sticks out like a sore thumb,” says Webb’s team member Jacob Bean of the University of Chicago. He says there have been some preliminary gas detections before, but none of them have been verified. Webb’s spectrum was “the right size, the right shape, and the right position,” Bean says. “CO2 just popped.”
Finding CO2 is valuable because it is a key to the planet’s “metallicity”—the proportion of elements heavier than helium in its composition. The hydrogen and helium produced in the big bang are the starting materials for all visible matter in the universe, but all the heavier stuff was forged later in the stars. Researchers believe that a good supply of heavy elements is crucial for the creation of giant planets. As planets form from a disk of material around a new star, the heavier elements form solid grains and pebbles that coalesce into a solid core that eventually becomes massive enough to pull in gases by its gravity and grow into a gas giant. With the Web, detection of “important chemicals will be the norm rather than the exception,” says one expert. He predicts that when Webb starts studying cooler planets close in size to Earth, there will be some real surprises – perhaps some gases that could indicate whether the planets are habitable. “It’s anyone’s guess,” he says. “A whole zoo of chemicals is possible.” The findings first appeared on the arXiv preprint server yesterday, and will appear in Nature soon.