A Hycean planet is a planet with a hydrogen-rich atmosphere and oceans of liquid water—and NASA says the James Webb Space Telescope may have spotted an intriguing one 120 light years away. Researchers say they have detected carbon-bearing molecules including methane and carbon dioxide in the atmosphere of K2-18b, suggesting it is a Hycean planet—and they've also found a possible sign of life. A team led by Nikku Madhusudhan, an astronomer at the University of Cambridge, says they may have detected the molecule dimethyl sulphide, which on Earth is only produced by life.
Madhusudhan says the team was "shocked" by the discovery. "The bulk of it in Earth's atmosphere is emitted from phytoplankton in marine environments," he tells the BBC. He says, however, the finding is "not robust." The team is conducting follow-up research and hopes to have more data to confirm the find in about a year. K2-18b, which orbits the cool dwarf star K2-18 in the Leo constellation, is believed to be around nine time the size of Earth, making it what astronomers call a "sub-Neptune"—a planet bigger than Earth but smaller than Neptune. "Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy," says team member Subhajit Sarkar.
"We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere," Sarkar says. The team says the investigation of K2-18b is just a preview of what Webb can detect in potentially habitable distant planets. "Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe," Madhusudhan says. "Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest." (More exoplanet stories.)
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