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The James Webb Space Telescope has placed the distant planet K2-18 b at the center of one of astronomy\u2019s most intense debates after detecting atmospheric chemicals that could\u2014but do not yet\u2014indicate biological activity. Located roughly 120 light-years from Earth in the constellation Leo, K2-18 b is a sub-Neptune with a mass nearly nine times that of Earth and an orbit inside its red dwarf star\u2019s habitable zone, where temperatures could potentially allow liquid water under suitable atmospheric conditions.<\/p>\n
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Webb observed the planet while it passed in front of its star, separating the wavelengths of starlight filtered through its atmosphere. Earlier measurements revealed methane and carbon dioxide, along with relatively little ammonia, a combination interpreted by some researchers as consistent with a possible \u201cHycean\u201d world possessing a hydrogen-rich atmosphere above a deep ocean. The most provocative claim concerns dimethyl sulfide, or DMS, and the related molecule dimethyl disulfide, known as DMDS. On Earth, DMS is produced mainly by biological activity, particularly marine microorganisms. A 2025 analysis of Webb\u2019s mid-infrared observations reported tentative evidence for DMS or DMDS at approximately three-sigma statistical significance.<\/p>\n
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That level is intriguing but remains well below the standard normally demanded for an extraordinary discovery, and the absorption patterns of different molecules can overlap. The study\u2019s authors explicitly stated that more observations were required and that possible non-biological production pathways must be investigated. Subsequent independent teams reprocessed the same Webb data using different software, wavelength groupings, and atmospheric models\u2014and reached considerably more cautious conclusions. One joint analysis found insufficient statistical evidence for either DMS or DMDS, noting that compounds such as ethane could reproduce similar features.<\/p>\n
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Another study warned that instrumental systematics and correlated noise in the mid-infrared measurements could create misleading spectral patterns. This disagreement illustrates why NASA has not confirmed alien life. Webb has confirmed that K2-18 b possesses an atmosphere containing carbon-bearing molecules, but the presence of a biosignature remains disputed, and even a reliable detection of DMS would not prove that organisms produced it. Scientists would still need to rule out unfamiliar geological, atmospheric, and photochemical processes on a type of planet that has no equivalent in our solar system.<\/p>\n
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Researchers also do not yet know whether K2-18 b contains a temperate ocean, a superheated interior beneath a thick atmosphere, or conditions hostile to life. The dramatic thumbnail accompanying the claim is therefore misleading: Webb cannot photograph animals, spacecraft, or surface inhabitants on K2-18 b. The winged figures and humanoid shapes are artistic fabrications rather than telescope data. What Webb actually records is a spectrum\u2014a pattern of light altered by molecules in a planet\u2019s atmosphere.<\/p>\n