Carbon Dioxide Detected Around Alien World For First Time

sciencehabit quotes a report from Science Magazine: Astronomers have found carbon dioxide (CO2) in the atmosphere of a Saturn-size planet 700 light-years away -- the first unambiguous detection of the gas in a planet beyond the Solar System. The discovery, made by the James Webb Space Telescope, provides clues to how the planet formed. The result also shows just how quickly Webb may identify a spate of other gases, such as methane and ammonia, which could hint at a planet's potential habitability for life. [...] For its 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 were taken on 10 July and the team started work on them a few days later. Even in raw data based on a single transit across the star, the spectral dip of CO2 "sticks out like a sore thumb," says Webb team member Jacob Bean of the University of Chicago. There have been some tentative detections of the gas before, he says, but none of them held up under scrutiny. Webb's spectrum was "the right size, the right shape, and in the right position," Bean says. "CO2 just popped out." Finding CO2 is valuable because it is a clue to a planet's "metallicity" -- the proportion of elements heavier than helium in its makeup. Hydrogen and helium produced in the big bang are the starting materials for all the visible matter in the universe, but anything heavier was forged later in stars. Researchers believe a good supply of heavy elements is crucial for creating giant planets. When planets form out of a disk of material around a new star, heavier elements form solid grains and pebbles that glom together into a solid core that eventually is massive enough to pull in gases with its own gravity and grow into a gas giant. With Webb, finding "important chemicals will be the norm rather than the exception," says one expert. He predicts that when Webb starts to study cooler planets closer in size to Earth, there will be some real surprises -- perhaps some gases that could indicate whether the planets are amenable to life. "It's anyone's guess," he says. "A whole zoo of chemicals is possible." The findings first appeared on the preprint server arXiv yesterday and they will appear in Nature in the near future.

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