By Sophie Jenkins

London, UK (SPX) - April 10, 2025 - Astronomers have unveiled groundbreaking findings that represent their most compelling evidence to date for potential biological activity on a planet located beyond our solar system. Although researchers stress the need for further verification, these discoveries could usher in a new era in the search for extraterrestrial life.

Utilizing the cutting-edge James Webb Space Telescope (JWST), a dedicated research team led by scientists from the University of Cambridge has identified the spectral signatures of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of exoplanet K2-18b. These molecules are known to be produced exclusively by life on Earth, primarily by ocean-dwelling microorganisms. The detection of such biosignatures is significant, signaling a major milestone in humanity's quest to find life beyond our planet.

K2-18b is situated within the habitable zone of its host star and lies approximately 124 light-years away from Earth in the constellation Leo. The planet is about 2.6 times larger than Earth and boasts a mass that is eight times greater. Earlier observations had already detected methane and carbon dioxide in its atmosphere, bolstering the hypothesis that K2-18b could be classified as a "Hycean" worlda planet that features a water-covered surface beneath a hydrogen-rich atmosphere.

The latest findings, which appear in a recent issue of The Astrophysical Journal Letters, reveal that the potential DMS/DMDS signal achieved a statistical significance of three sigma. This indicates a mere 0.3% chance that the observation is a mere coincidence. For formal scientific confirmation, a five-sigma detection is required, which would reduce that likelihood to less than 0.00006%. To attain this threshold, the research team estimates that an additional 16 to 24 hours of observation time using the JWST will be necessary.

The earlier tentative detection of DMS was conducted using the JWST's NIRISS and NIRSpec instruments, which operate in the near-infrared spectrum. The new signal was detected using a distinct method: the MIRI (Mid-Infrared Instrument) of JWST, which specializes in observing mid-infrared wavelengths ranging from 6 to 12 microns. This consistency in data obtained from different instruments and wavelength ranges enhances confidence in the reliability of the detection.

Professor Nikku Madhusudhan, the project lead at the University of Cambridge's Institute of Astronomy, emphasized, "This is an independent line of evidence, utilizing a different instrument than we did before and measuring a different wavelength range of light, where there is no overlap with the previous observations. The signal came through strong and clear."

Interestingly, K2-18b's atmosphere seems to contain DMS and DMDS at levels significantly higher than those found on Earth. These molecules typically do not exceed one part per billion in our planet's atmosphere; however, on K2-18b, estimates suggest concentrations exceeding ten parts per million.

Madhusudhan stated that these findings align with earlier theoretical models, which predicted that Hycean planets could host elevated levels of sulfur-based gases. He elaborated, "Given everything we know about this planet, a Hycean world with an ocean teeming with life is the scenario that best fits the data we have."

Despite the optimistic findings, researchers urge caution and emphasize the necessity of continued investigation. There remains the possibility that unknown non-biological mechanisms could account for the observed presence of these molecules. Future theoretical and experimental studies are planned to explore whether such chemicals could be generated abiotically under unusual planetary conditions.

Co-author Subhajit Sarkar from Cardiff University remarked, "The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them." The team is committed to rigorous scrutiny, highlighting the importance of maintaining a skeptical approach towards their own results. Madhusudhan reiterated, "It's important that we're deeply skeptical of our own results, because it's only through extensive testing that we will achieve confidence in our conclusions."

With the advanced capabilities of the JWST and promising future telescopes on the horizon, astronomers are optimistic that they may be closer than ever to answering a fundamental question that has puzzled humanity for centuries: Are we alone in the universe?

Madhusudhan concluded with an intriguing thought, stating, "Decades from now, we may look back at this point in time and recognize it as the moment when the living universe came within reach. This could be the tipping point." The James Webb Space Telescope is a collaborative mission undertaken by NASA, the European Space Agency (ESA), and the Canadian Space Agency. This groundbreaking research was made possible through funding from a UK Research and Innovation (UKRI) Frontier Research Grant.

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