What it is
Using JWST's MIRI instrument, the team measured a mid-infrared transmission spectrum of the sub-Neptune K2-18 b across the 6 to 12 micron range. The spectrum is inconsistent with a flat, featureless atmosphere at 3.4 sigma and, of the molecules modeled, is best matched by dimethyl sulfide (DMS) and dimethyl disulfide (DMDS). This yields new, independent evidence for at least one of the two gases at 3 sigma, with a high inferred abundance of at least 10 ppmv.
Why it matters
DMS and DMDS are produced almost entirely by life on Earth, so their possible presence on a distant world is one of the most consequential claims in exoplanet science. This is a separate instrument and wavelength band from the earlier near-infrared hint, so an echo of the same signal at 3 sigma is harder to dismiss as an artifact. It also concentrates attention on K2-18 b as the leading test case for whether a hycean (ocean-and-hydrogen) world can be characterized at all.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underexoplanets, JWST, biosignatures, K2-18 b, spectroscopy