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Sign inFrom the JWST MIRI LRS transmission spectrum (5–12 µm) the paper reports a deviation from a featureless spectrum at 3.4σ and 'evidence for DMS and/or DMDS' at about 3σ, with at least one at ppmv. On Earth these gases are produced predominantly by life, so the claim was presented as a possible biosignature. A robust detection would require reproducing the attribution across data reductions, retrieval frameworks and alternative molecules.
Independent reanalyses of the same public data (Luque et al.; Welbanks et al.; Stevenson et al.; Schmidt et al.; Lavvas et al.) find no statistically significant DMS/DMDS: the signal depends on binning, red noise and the set of molecules considered, and hazy models fit without DMS. The original authors have not withdrawn the claim; a follow-up co-authored by Madhusudhan (Hu et al., four new NIRSpec transits) finds DMS below 3σ.
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Luque et al. find insufficient evidence in a joint 0.6–12 µm fit, with ethane and other methyl-bearing species fitting equally well.
Stevenson et al. find binning-dependent red noise dominates the MIRI spectrum and 87.5% of retrievals with their preferred binning do not favour DMS/DMDS.
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Welbanks et al. show the claimed evidence disappears once a broader set of atmospheric models is compared.
Luque et al. estimate about 25 more MIRI transits would be needed. No new JWST observations of K2-18 b had been published by October 2026.