K2-18b: Exoplanet Profile

Exoplanet K2-18b: Located 124 light-years away in the Leo constellation, orbiting the star K2-18. Discovered in 2015 by the Kepler Space Telescope.

Size and Atmosphere: Approximately 5.2 times wider and 9 times more massive than Earth. Thought to have a hydrogen-rich atmosphere.

Past Discoveries: Hubble Space Telescope detected water vapour in 2019. James Webb Space Telescope (JWST) found carbon dioxide and methane.

DMS/DMDS Detection: In 2025, researchers reported detecting either dimethyl sulphide (DMS) or dimethyl disulphide (DMDS) in K2-18b’s atmosphere.

Significance of DMS: On Earth, DMS is primarily produced by phytoplankton and considered a potential biomarker (sign of life).

Hycean World Candidate: K2-18b is hypothesized to be a Hycean world which is a planet covered with a liquid ocean and a hydrogen rich atmosphere.

Contradictory Findings: Some studies challenge the initial findings, one 2024 paper said that JWST observations can be explained by K2-18b being “a gas-rich mini-Neptune”. One 2025 paper confirms the presence of methane but yields “no statistically significant or reliable evidence for carbon dioxide or DMS.

Cautions about Habitability: Detecting potential biomarkers is suggestive, not confirmatory, of habitable conditions. Non-biological processes could also create such molecules.