Only living organisms on Earth, mainly marine phytoplankton, produce these molecules. This finding constitutes the strongest evidence yet of a biosignature—a potential sign of extraterrestrial life outside the solar system. According to the study, published in The Astrophysical Journal Letters, confirming the signal will require an additional 16 to 24 hours of observations with the JWST.
What K2-18b looks like. K2-18b is a “sub-Neptune,” a planet with 8.6 times the mass and 2.6 times the radius of Earth. It orbits a red dwarf in the habitable zone, receiving an energy flux from its star similar to what Earth receives from the sun. The planet lies 124 light-years away in the constellation Leo.
It’s also a candidate for classification as a Hycean planet—worlds that could harbor global oceans beneath hydrogen-rich atmospheres. Earlier JWST observations already detected methane and carbon dioxide in its atmosphere, supporting this scenario.
Reasons for optimism. As the planet passes in front of its star, some starlight filters through its atmosphere. Each molecule in the atmosphere leaves a specific pattern in the spectrum. Scientists have seen the same spectral pattern for dimethyl sulfide twice since 2023 using JWST’s MIRI instrument.
This could be the first coherent biosignature detected on a planet outside the solar system. If confirmed, it would suggest that life might be more common on planets larger than Earth. Hycean planets could become key targets in the search for extraterrestrial life, which so far has focused mostly on rocky worlds like super-Earths.
Reasons for caution. Still, several unknowns remain—especially regarding temperature. Previous research suggested K2-18b might be a magma ocean world, with a gaseous mantle that would be too extreme for life as we know it.
And while dimethyl sulfide is biological in origin on Earth, researchers acknowledge that it might result from exotic geochemical reactions in a high-pressure, hydrogen-rich environment. Additional modeling and lab experiments will be needed to determine whether this signal truly points to life.
Image | University of Cambridge
The post The Webb Telescope Has Been Searching for Extraterrestrial Life for Years. It Has Just Detected the Strongest Signal Yet on the Exoplanet K2-18b appeared first on Xataka On.
