Astronomers detected dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of exoplanet K2-18b. These sulfur-containing molecules are significant because on Earth, they are primarily produced by marine microbial life, making them potential biosignatures that suggest biological activity on K2-18b.

A Hycean world is a type of exoplanet characterized by a global ocean beneath a hydrogen-rich atmosphere, potentially providing a warm oceanic environment suitable for life. K2-18b is considered a candidate Hycean world because it is roughly 2.6 times Earth's radius, 8.6 times its mass, and likely possesses a hydrogen-rich atmosphere along with a surface ocean, placing it in the habitable zone around its star.

The detection of DMS and/or DMDS on K2-18b has reached a three-sigma level of statistical significance, meaning there is a 0.3% probability the signal occurred by chance. However, to confirm a scientific discovery, a five-sigma threshold is typically required, corresponding to a 0.00006% probability of chance. Additional JWST observations totaling 16 to 24 hours are planned to reach this higher confidence level.

Researchers emphasize caution in interpreting the detected chemical signatures as evidence of life, noting that unknown non-biological chemical processes could potentially produce DMS and DMDS. They stress the need for further theoretical, experimental, and observational work to validate these findings before claiming definitive evidence of extraterrestrial life.

If confirmed, the detection of biosignature molecules on K2-18b would represent the strongest evidence yet of life beyond our solar system, potentially marking a tipping point in humanity’s search for extraterrestrial life. It would support the idea that life may be common in the universe, especially around the most common type of stars—red dwarfs—and that microbial life could be widespread across exoplanets within habitable zones.