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Possible biosignatures detected on Exoplanet K2-18b, raising hopes for alien life

By isabelle // 2025-04-19

• Astronomers found potential biosignatures of life on exoplanet K2-18b using the James Webb Space Telescope.
• Dimethyl sulfide (DMS), a molecule linked to life on Earth, was detected in K2-18b’s atmosphere.
• Scientists remain cautious, needing further data to confirm the findings at a five-sigma confidence level.
• If verified, this would be the first evidence of life-supporting conditions on a habitable exoplanet.
• The discovery could redefine how we search for extraterrestrial life, prioritizing sulfur-based molecules.

Astronomers have announced the strongest evidence yet for extraterrestrial life after detecting traces of two Earth-biosphere signatures in the atmosphere of the exoplanet K2-18b, a planet 124 light-years away. Using NASA’s James Webb Space Telescope (JWST), researchers observed chemical fingerprints suggesting the presence of dimethyl sulfide (DMS) and its cousin dimethyl disulfide (DMDS)—molecules produced almost exclusively by living organisms on Earth. The findings, detailed in The Astrophysical Journal Letters, could represent a landmark in humanity’s search for life beyond our solar system, though experts caution against declaring such a discovery prematurely.

K2-18b’s detections stir excitement and caution

K2-18b, a so-called Hycean world suspected to host a vast ocean beneath a hydrogen-rich atmosphere, was targeted based on its potential to harbor liquid water and moderate temperatures. Previous studies identified carbon dioxide and methane in its atmosphere, but the new analysis adds sulfur-based molecules to the mix. DMS on Earth is produced primarily by marine phytoplankton, spurring researchers to suggest similar organisms might exist there. “This is a revolutionary moment. It’s the first time humanity has seen potential biosignatures on a habitable planet,” said lead author Nikku Madhusudhan, an astrophysicist at Cambridge University. “The signal came through strong and clear.” The team used JWST’s Mid-Infrared Instrument (MIRI) to replicate 2023 findings from other JWST instruments, boosting confidence in the detection. The analyses, however, come with caveats. Study coauthor Subhajit Sarkar noted, “The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them.” While DMS concentrations were estimated at over 10 parts per million — thousands of times higher than Earth — the results are preliminary.

The long road to confirmation

Scientists emphasize that correlation is not causation. Hycean worlds, proposed by Madhusudhan in 2021, are speculative and could exhibit non-biological behaviors. The lack of observed ethane — a byproduct that would form if DMS were present — puzzles some experts, as University of California researcher Eddie Schwieterman noted: “The absence of ethane makes me think we’ve missed something.” Currently, the findings have reached a three-sigma significance — 99.7% confidence — but a five-sigma threshold (99.99994% certainty) is needed to claim discovery. Madhusudhan argues this milestone “ushers in a new era” but acknowledges needed groundwork: 16–24 additional hours of JWST time and independent replication by other teams after data release next week. The discovery arrives amid a rapid evolution in exoplanet science. JWST, launched in 2021, enables finely detailed atmospheric analysis of distant worlds, while the Hycean concept has redefined habitability targets beyond Earth-like planets. As debates continue, the data holds profound implications. If confirmed, DMS and DMDS could join oxygen as canonical biosignatures. But even if disproven, the study fuels a new strategy: prioritizing sulfur molecules instead of traditional candidates. “In my mind, it is no longer a question of whether we will find life if such life exists,” Madhusudhan said. “We have demonstrated that we have the capability to do so with our initial current findings at reasonable significance. A bigger question in my mind is whether we as a species are prepared to find life as we don’t know it. We as a society, as a species, should come together and ask ourselves the question: What is it that constitutes life elsewhere?” The search for life isn’t just about telescopic data — it’s a cultural reckoning. As the scientific community holds its breath, K2-18b remains a mirror reflecting our hopes, our skepticism, and our audacity to seek answers in the dark beyond Earth. Sources for this article include: YourNews.com CNN.com Space.com

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