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<\/p>\nThe James Webb Space Telescope has detected intriguing chemical signals in the atmosphere of K2-18 b, a distant exoplanet that has become one of the most closely watched targets in the search for life beyond Earth.<\/p>\n
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Located approximately 124 light-years away in the constellation Leo, K2-18 b orbits within the habitable zone of a cool red-dwarf star, where temperatures could theoretically permit liquid water under suitable atmospheric conditions. Webb\u2019s observations have confirmed methane and carbon dioxide in the planet\u2019s hydrogen-rich atmosphere, while showing relatively little ammonia\u2014a combination that some researchers believe may be consistent with a vast ocean beneath the atmosphere. More recent data from Webb\u2019s Mid-Infrared Instrument revealed possible absorption features associated with dimethyl sulfide, or DMS, and dimethyl disulfide, known as DMDS.<\/p>\n
On Earth, DMS is produced mainly by living organisms, particularly microscopic marine life, making it an interesting potential biosignature. The research team reported the signal at approximately three-sigma significance, corresponding to a statistical confidence near 99.7 percent under the assumptions of its model. However, that figure describes confidence in a feature within the data; it does not mean there is a 99.7 or 99.9 percent probability that life exists on the planet. Random noise, instrumental effects, data-processing choices, or another molecule with a similar infrared signature could potentially create the same pattern.<\/p>\n
Independent researchers analyzing Webb\u2019s complete spectrum have subsequently found insufficient evidence to confirm either DMS or DMDS, demonstrating that the interpretation remains controversial. K2-18 b is also very different from Earth. It has a radius approximately 2.6 times greater than Earth\u2019s and a mass more than eight times larger, placing it in the category of sub-Neptune planets. Scientists do not yet know whether it possesses a habitable ocean, a deep layer of high-pressure ice, or an atmosphere so thick that conditions below would be hostile to known life.<\/p>\n
The European Space Agency stresses that occupying a star\u2019s habitable zone and containing carbon-bearing molecules do not automatically make a planet habitable. Webb has not photographed continents, artificial lights, cities, or biological organisms on K2-18 b. The richly detailed planet shown in the accompanying thumbnail is an artistic visualization, because the exoplanet appears to telescopes only as unresolved light passing in front of its star.<\/p>\n
Astronomers determine atmospheric composition by studying the tiny portion of starlight filtered through the planet\u2019s gases during a transit. Different molecules absorb characteristic wavelengths, leaving chemical fingerprints in the spectrum. Confirming life would require repeated observations, stronger statistical evidence, independent analyses, and the elimination of plausible nonbiological chemistry.<\/p>\n