'These Are the First Hints' of an Inhabited Alien World

Researchers peering into the cosmos with help from the James Webb Space Telescope say they've uncovered the strongest sign yet of extraterrestrial life. It comes from K2-18b, a planet with about 2.5 times the radius of Earth that resides in the constellation Leo, some 120 light-years away. The planet was discovered in 2017 but drew attention in 2023 when researchers studying the planet's atmosphere announced the possible detection of the molecule dimethyl sulphide, which on Earth is only produced by living organisms—"particularly by marine microbes," per NPR. A second analysis has now turned up more evidence.

Using a different instrument on the Webb telescope to analyze K2-18b's illuminated atmosphere as the planet passed in front of its host star, researchers detected even stronger signals of dimethyl sulfide—so strong as to suggest K2-18b's level of the molecule is thousands of times higher than Earth's, the New York Times reports. They also detected the similar molecule dimethyl disulfide, also produced through biological processes. "These are the first hints we are seeing of an alien world that is possibly inhabited," University of Cambridge astronomer Nikku Madhusudhan, lead author of a study published Wednesday in Astrophysical Journal Letters, said at a Tuesday press conference, per NPR. "This is a revolutionary moment."

Others are more cautious. "It's a hint. But we cannot conclude it's habitable yet," Johns Hopkins University planetary scientist Stephen Schmidt says, per the Times. While Madhusudhan's team believes K2-18b to be an as-yet hypothetical Hycean planet, with a hydrogen-rich atmosphere and oceans of liquid water, another paper argues K2-18b may instead be largely rock with a magma ocean under a thick hydrogen atmosphere. Even Madhusudhan acknowledges more study is needed to confirm the detection of these molecules and show they aren't produced outside of biological processes. Still, "it's the first time humanity has seen potential biosignatures on a habitable planet," he tells the Times. (More discoveries stories.)