In April, an announcement electrified the scientific community: Researchers had detected dimethyl sulfide (DMS), a molecule associated with biological life, in the atmosphere of exoplanet K2-18b. If confirmed, it could be one of the most tantalizing hints of alien life ever found.
But a new study led by University of Chicago scientists is stifling the excitement, arguing that the data is too noisy to make such a groundbreaking claim. Their analysis suggests that other, more mundane molecules—like ethane—could equally explain the spectral readings from the James Webb Space Telescope, urging caution before declaring a cosmic biological breakthrough.
K2-18b, a planet 124 light-years from Earth, has long intrigued scientists because its hydrogen-rich atmosphere hints at potential habitability. The April 16 announcement, led by Cambridge researchers, suggested Webb’s infrared observations confirmed the presence of either dimethyl sulfide or dimethyl disulfide—compounds that, on Earth, are only linked to biological activity.
However, the Chicago team, led by postdoctoral researcher Rafael Luque, reanalyzed Webb’s readings alongside data from other telescopes, including Hubble.
Astronomers discover possible signs of life on exoplanet K2-18b
Their conclusion?
The spectral signals attributed to DMS could just as easily belong to ethane, a common gas found in the atmospheres of giant planets like Neptune, which is not connected to life.
“Anything with a carbon bonded to three hydrogens will show up at this wavelength,” explained study co-author Michael Zhang. “Dimethyl sulfide does—but so do many other molecules. Even with better data, it will be hard to identify DMS uniquely.”
Researchers argue that the key issue is that the original detection relied on a single observation pass from Webb. In contrast, multi-pass observations, when combined, paint a much less convincing case for DMS.
“We should always favor the simplest explanation first,” said co-author Caroline Piaulet-Ghorayeb. “If ethane—something we know exists on planets in our solar system—can explain the data, then we shouldn’t jump to an exotic molecule like dimethyl sulfide unless all other possibilities have been ruled out.”
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While K2-18b remains one of the most promising targets in the search for habitable worlds, the study underscores an important principle: caution. Luque and his team emphasize that progress in exoplanet science is accelerating, but misleading declarations could overshadow serious advances.
“Finding life beyond Earth is the ultimate goal of our field,” Luque said. “But we need robust proof, not excitement-driven assumptions.”
The quest for unmistakable biosignatures will continue as the Webb Telescope gathers more observations and future missions refine detection techniques. Until then, the search for life among the stars remains an open question, awaiting the proper evidence to tilt the scales.
Journal Reference:
- R. Luque et al., Insufficient evidence for DMS and DMDS in the atmosphere of K2-18 b. From a joint analysis of JWST NIRISS, NIRSpec, and MIRI observations, arXiv (2025). DOI: 10.48550/arxiv.2505.13407
