Washington DC [US], April 24 (HBTV): Astronomers using the James Webb Space Telescope (JWST) have detected chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of the exoplanet K2‑18b, providing the most promising biosignature to date beyond our solar system.

On Earth, DMS and DMDS are exclusively produced by life—primarily marine phytoplankton—making their presence on K2‑18b a potential indicator of biological activity. The team, led by Professor Nikku Madhusudhan of the University of Cambridge, reported the findings in The Astrophysical Journal Letters.

The detection reached a three‑sigma level of statistical significance, corresponding to a 0.3 per cent probability of being a fluke. To achieve a definitive discovery, the observations must cross the five‑sigma threshold (0.00006 per cent chance of randomness). The researchers estimate an additional 16–24 hours of JWST follow‑up observations could secure the five‑sigma confirmation.

K2‑18b, situated 124 light‑years away in the constellation Leo, is 8.6 times as massive and 2.6 times as large as Earth. Earlier JWST data revealed methane and carbon dioxide—marking the first discovery of carbon‑based molecules in a habitable‑zone exoplanet and supporting the ‘Hycean’ world hypothesis of an ocean beneath a hydrogen‑rich atmosphere. A weaker signal in those data hinted at DMS, prompting this new MIRI (Mid‑Infrared Instrument) investigation, which covers 6–12 microns and is independent of prior NIRISS and NIRSpec near‑infrared (0.8–5 micron) observations.

‘This is an independent line of evidence, using a different instrument and wavelength range, where there is no overlap with previous observations,’ said Madhusudhan. ‘The signal came through strong and clear.’ Co‑author Mans Holmberg of the Space Telescope Science Institute added, ‘It was an incredible realization seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests.’

The technique involves analysing starlight filtered through the planet’s atmosphere during transit, with absorption features revealing constituent gases. While an unknown abiotic process might conceivably produce DMS or DMDS, the new results stand as the strongest evidence yet for extraterrestrial life.

Future JWST observations and subsequent missions targeting other sulfate‑rich exoplanets may confirm these findings and further illuminate the conditions for habitability—and possible biology—on distant worlds.

(ANI)