With detection of best ever signs of life on K2-18b, JWST clears hurdle in hunt for alien life

In a milestone for exoplanet research, scientists using the James Webb Space Telescope (JWST) have strengthened evidence for potential signs of life on a distant planet by ruling out instrument-based errors.

The study, titled “New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI” (DOI 10.3847/2041-8213/adc1c8), by Nikku Madhusudhan, Savvas Constantinou, Måns Holmberg, Subhajit Sarkar, Anjali A. A. Piette and Julianne I. Moses and published yesterday in The Astrophysical Journal Letters, presents the first mid-infrared transmission spectrum of K2-18b, a planet orbiting a cool dwarf star 124 light-years from Earth.

The team targeted two sulfur-based gases: dimethyl sulfide (DMS) and dimethyl disulfide (DMDS). Both are produced biologically on Earth, but are virtually unknown from non-biological processes. Previous studies hinted at DMS in the planet’s atmosphere, but the detection lacked statistical weight and could not exclude observational artifacts.

This new effort — using JWST’s MIRI instrument, which views a different portion of the infrared spectrum — delivers a separate and statistically significant detection. The spectral signature could not be explained by simpler molecules like carbon dioxide or methane alone. Importantly, the data eliminates the possibility of a flat, featureless atmosphere with more than 99.7% certainty.

By observing in a new wavelength range (6–12 microns), the researchers overcame challenges from earlier JWST data, where DMS signals overlapped with those of methane. Now, even when processed through two completely independent data pipelines, the same result emerged: either DMS or DMDS appears present in relatively high quantities, estimated above 10 parts per million by volume.

Importantly, the study authors emphasized that while the detection reaches a 3σ confidence level — a commonly accepted threshold for tentative discoveries — it does not yet meet the higher standard required for confirmation. Still, the consistency across different instruments and methods greatly reduces the odds that the signals are false positives.

Another key finding was that these gases were the only ones — out of 20 biosignature and background candidates — to produce consistent matches to the observed spectrum. No significant contributions from water vapor, carbon monoxide or ammonia were found in the MIRI band.

This work also demonstrated JWST’s ability to deliver robust results even in the presence of time-correlated noise and instrumental variation — providing a technical validation as much as a scientific one. By employing statistical cross-checks and leave-one-out tests, the researchers confirmed that the spectral features weren’t dominated by any single data point or pipeline artifact.

While the presence of DMS and DMDS alone does not confirm life on K2-18b, this study marks a turning point: it shows that we now have the tools to independently verify biosignature gases across multiple observations, a critical step toward ruling out false alarms in the search for life beyond Earth.

The text in this work is licensed under CC BY 4.0

Featured photo is an AI-rendered image of exoplanet K2-18b