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New Evidence for the Existence of Life Beyond our Solar System [1]

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Date: 2025-04-18

This has gotten a fair amount of coverage in the science-oriented media today, but apparently hasn’t been mentioned here yet. It seems we have our best evidence by far now that life as we know it (i.e. carbon-based life forms) may indeed exist beyond the confines of our own solar system — even if they may just be microbial in nature. From physics.org:

Astronomers have detected the most promising signs yet of a possible biosignature outside the solar system, although they remain cautious. Using data from the James Webb Space Telescope (JWST), the astronomers, led by the University of Cambridge, have detected the chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), in the atmosphere of the exoplanet K2-18b, which orbits its star in the habitable zone. On Earth, DMS and DMDS are only produced by life, primarily microbial life such as marine phytoplankton. While an unknown chemical process may be the source of these molecules in K2-18b's atmosphere, the results are the strongest evidence yet that life may exist on a planet outside our solar system. The observations have reached the 'three-sigma' level of statistical significance—meaning there is a 0.3% probability that they occurred by chance. To reach the accepted classification for scientific discovery, the observations would have to cross the five-sigma threshold, meaning there would be below a 0.00006% probability they occurred by chance. The researchers say between 16 and 24 hours of follow-up observation time with JWST may help them reach the all-important five-sigma significance. Their results are reported in The Astrophysical Journal Letters. Earlier observations of K2-18b—which is 8.6 times as massive and 2.6 times as large as Earth, and lies 124 light years away in the constellation of Leo—identified methane and carbon dioxide in its atmosphere. This was the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in the habitable zone.

K2-18b is presumed to be a ‘Hycean’ planet, meaning a completely ocean-covered world with a thick hydrogen-rich atmosphere.

.. However, the concentrations of DMS and DMDS in K2-18b's atmosphere are very different than on Earth, where they are generally below one part per billion by volume. On K2-18b, they are estimated to be thousands of times stronger—over ten parts per million. "Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds," said Madhusudhan. "And now we've observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have." … While he is not yet claiming a definitive discovery, Madhusudhan says that with powerful tools like JWST and future planned telescopes, humanity is taking new steps toward answering that most essential of questions: are we alone? "Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach," said Madhusudhan. "This could be the tipping point, where suddenly the fundamental question of whether we're alone in the universe is one we're capable of answering."

Meanwhile closer to home, NASA’s Curiosity Rover on Mars has found new evidence of how the Red Planet’s once thick atmosphere that presumably supported a warmer, wetter, and potentially habitable surface collapsed into the cold, dry, and extremely inhospitable world we know today — also from pyhsics.org:

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