James Webb '99.7% life' video

The object here is an exoplanet spectrum — basically a tiny fingerprint in starlight. And the stakes are huge, because if James Webb really had found a convincing biosignature, that would be the closest thing we’ve ever had to evidence for life beyond Earth. But that is not what “99.7% life” means, and turns out that phrase mashes together three different ideas that scientists keep separate. The underlying claim traces back to K2-18 b, a planet 124 light-years away, and a University of Cambridge team’s April 17, 2025 paper on possible sulfur molecules in its atmosphere. (arxiv.org) ### What did Webb actually see? Webb did not photograph aliens, oceans, or microbes. It measured how starlight filtered through K2-18 b’s atmosphere during a transit, then researchers tried to match the resulting spectrum to candidate molecules. In 2023, Webb data already showed methane and carbon dioxide, plus a tentative hint of dimethyl sulfide, or DMS. The April 2025 paper added mid-infrared dat(arxiv.org)MS and/or dimethyl disulfide, DMDS, best explained part of the signal. (science.nasa.gov) ### Where did the 99.7% come from? From a stats shortcut — and a misleading one. The Cambridge team described the new signal as roughly 3-sigma, which they framed as a 0.3% probability that the feature happened by chance. Flip that around and you get 99.7% confidence that the feature is not random noise. But that is not the same as 99.7% confidence in life. It is confidence in a pattern in the data under a specific model. (cam.ac.uk) ### Why isn’t that the same as life? Because there are two jumps here, not one. First, you have to show the molecule is really there. Then you have to show biology is the best explanation for that molecule. Even the Cambridge paper said more observations were needed, that DMS and DMDS were partly degenerate with each other, and that scientists still need better lab data and a better handle on possible non-biological sources. (arxiv.org) ### Is DMS a big deal anyway? Yes — but carefully yes. On Earth, DMS is associated with life, mostly marine microbes, which is why people got excited. NASA’s earlier K2-18 b page called DMS only a “possible detection,” and the Cambridge release itself said the team remained cautious. A biosignature is a clue, not a verdict. Think smoke alarm, not confirmed fire. (science.nasa.gov)rbon-dioxide-in-atmosphere-of-k2-18-b/)) ### Did anyone challenge the claim? Very quickly. On May 19, 2025, another team posted a reanalysis of the combined JWST data — NIRISS, NIRSpec, and MIRI — and said there was insufficient evidence for DMS or DMDS in K2-18 b’s atmosphere. They also argued that other molecules, including ethane, could fit the same spectral re(science.nasa.gov)way ahead of the science. (arxiv.org) ### What about the “100x faster than Webb” telescope line? That’s another category error. Some next-gen concepts have been described as collecting 100 times more light than Webb, and NASA’s SPHEREx is often hyped as more powerful in some ways. But SPHEREx is a wide-field all-sky survey mission that complements Webb rather than replacing it. Webb is a targeted observatory for deep, detailed follow-up(arxiv.org)ing if you specify the job. (singularityhub.com) ### So what should you take from this? K2-18 b is still interesting. Webb really did produce intriguing data, and biosignature science is moving from theory into actual measurement. But the honest version is narrower and more exciting in a grown-up way: scientists may have seen a puzzling (singularityhub.com) frontier science looks before the dust settles. (arxiv.org)