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Astronomers Detect Potential Biosignatures on Distant Exoplanet K2-18b

JWST data reveals dimethyl sulfide and dimethyl disulfide at 99.7% confidence, but further observations are needed to confirm biological origins.

Visual representation of Exo-Planet K2-18b.
A graph shows the observed transmission spectrum of the habitable zone exoplanet K2-18 b using the James Webb Space Telescope MIRI spectrograph instrument. The vertical shows the fraction of star light absorbed in the planet's atmosphere due to molecules in its atmosphere. The data are shown in the yellow circles with the 1-sigma uncertainties. The curves show the model fits to the data, with the black curve showing the median fit and the cyan curves outlining the 1-sigma intervals of the model fits. The absorption features attributed to dimethyl sulphide and dimethyl disulphide are indicated by the horizontal lines and text. The image behind the graph is an illustration of a hycean planet orbiting a red dwarf star. This image was obtained by Reuters on April 16, 2025. A. Smith, N. Madhusudhan/University of Cambridge/Handout via REUTERS NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.
Image
An artist's concept shows what exoplanet K2-18 b could look like based on science data. The illustration was released on September 11, 2023. NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)/Handout via REUTERS NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.

Overview

  • Researchers using the James Webb Space Telescope have identified dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of K2-18b, gases on Earth produced only by marine microorganisms.
  • The detection was made at a three-sigma confidence level (99.7%), falling short of the five-sigma standard (99.99994%) required to confirm the presence of life.
  • K2-18b, located 124 light-years away, is classified as a 'hycean world,' with a hydrogen-rich atmosphere and a hypothesized global ocean that may support microbial life.
  • Additional 16–24 hours of telescope observations and extensive theoretical studies are planned to rule out non-biological explanations for the detected gases.
  • Experts remain cautious, noting that previous three-sigma findings on K2-18b did not hold up under scrutiny and that unknown abiotic processes could mimic the biosignature signals.