News involving the discovery of possible biosignatures in the atmosphere of exoplanet K2-18b recently brought the search for alien life to the forefront of scientific debate. However, a recent analysis by an Oxford University physicist is now casting doubt on the idea, suggesting the signals in question could have an alternate explanation.
Located 120 light years from Earth in the constellation Leo, K2-18b has long attracted astronomers’ attention for its potential habitability. Last year, the promising exoplanet made headlines when it was learned that astronomers had reported possible signs of dimethyl sulfide (DMS), a molecule on Earth typically associated with life, in its atmosphere.
Often associated with small marine organisms like phytoplankton, the data made possible through observations by the James Webb Space Telescope (JWST) appeared to provide the most tantalizing data yet involving potential evidence of life on another planet. The findings would seemingly indicate that K2-18b might be what astronomers call a rare “Hycean” world, entailing a planet with a hydrogen-rich atmosphere above a global ocean.
However, in a new study posted this week on arXiv by Dr. Jake Taylor of Oxford’s Department of Physics, questions about those findings now challenge the likelihood that the discovery may be a strong indication of life on an alien world.
Based on his analysis, Taylor argues there is no strong statistical evidence for the presence of DMS or other biosignature gases based on data from the Webb telescope’s mid-infrared (MIRI/LRS) transmission spectrum of the planet.
“Despite the claim of a 3.4-sigma deviation from a flat line,” Taylor writes in his paper, “I find a flat line is an acceptable fit.”
Employing a Gaussian feature analysis to help look for any statistically significant absorption features present in the spectrum, Taylor essentially went in search of any telltale “dips” that would lend support to the idea that certain molecules present may be absorbing starlight as it passed through K2-18b’s atmosphere.
In five out of six tests, Taylor found that the data is better explained by a flat spectrum than one bearing the spectrographic hallmark of molecules.
Taylor reports that even while testing for features at specific wavelengths where DMS and other similar compounds are expected to appear, only weak statistical support, equivalent to about a 2-sigma detection, could be found.
This places the data below the threshold typically required for confident claims in astrophysics.
“Therefore, there is no strong evidence for detected spectral features in K2-18b’s MIRI transmission spectrum,” Taylor concludes.
The new findings also potentially raise concerns about how prior studies derived their results. Primarily, the original team’s atmospheric models may have overstated the significance of spectral features by overlooking alternative molecules and fixing parameters in a way that could have superficially boosted the evidence for biosignatures.
Although the new findings do not completely rule out the presence of DMS or similar compounds in K2-18b’s atmosphere, they do reveal new questions and also the need for caution.
“Only when fixing the Gaussians to specific wavelengths do I see any deviation from a flat line,” he notes, adding that more agnostic, model-independent approaches result in spectra consistent with no atmospheric features at all.
The Debrief reached out to Dr. Taylor for further comment on the Gaussian model tests and their relationship to interpretations of possible biosignatures, but as of the time of publication, it had not received a reply.
Fundamentally, Taylor’s research highlights the problems inherent to interpreting faint spectral signals across vast distances, underscoring how the search for life on faraway worlds, however convincing it may seem, still relies on tentative data for now.
Taylor’s paper, “Are there Spectral Features in the MIRI/LRS Transmission Spectrum of K2-18b?,” appeared on the arXiv.org preprint server on April 22, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.