The exoplanet K2-18b, located about 120 light-years away in the constellation Leo, has been at the center of excitement in the search for extraterrestrial life. Earlier reports suggested the possible detection of gases such as dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in its atmosphere – molecules that, on Earth, are associated with biological activity. These findings raised speculation that K2-18b might host life. However, the new study carefully reexamines these claims and concludes that the evidence does not meet the rigorous standards required for a credible detection of biosignatures.

The authors reanalyzed James Webb Space Telescope data using multiple independent data reduction pipelines and spectral retrieval methods. Their focus was on MIRI transit spectroscopy, which had been central to the original biosignature claim. They found that the MIRI data are highly vulnerable to instrumental systematics and red noise, which can easily produce misleading features that appear biological but are in fact artifacts of the instrument.

One key test was wavelength binning. By slightly changing how the data were grouped into bins, the researchers obtained very different spectral signatures. In most cases the supposed DMS/DMDS signal disappeared entirely. This strongly suggests that the earlier detections were not robust but rather a by-product of specific data handling choices.

When analyzing the broader transit spectrum, the study found strong, consistent evidence for methane and carbon dioxide in K2-18b’s atmosphere. However, the data could not uniquely distinguish between DMS and other molecules such as ethylene, which provide equally good fits. This lack of uniqueness undermines any claim of a biosignature detection.

The authors stress the importance of applying a “standards of evidence” framework for claims of life detection. To be credible, a biosignature must be reproducible across different data processing techniques, statistically significant beyond noise and instrumental artifacts and uniquely attributable to biological rather than abiotic processes. The K2-18b data currently fail on all three counts.

The study concludes that there is no statistically significant evidence of biosignature gases in K2-18b’s atmosphere. Instead, the earlier claims most likely reflect limitations in the MIRI data, not actual signs of life.