Scientists Find Strong Evidence of Life on Exoplanet K2-18b

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Scientists Detect Strongest Evidence Yet of Potential Life on Exoplanet K2-18b

By TRH News Desk

New Delhi, April 17, 2025: A groundbreaking study published in The Astrophysical Journal Letters sparked global excitement with the detection of chemical signatures on exoplanet K2-18b, located 124 light-years away in the constellation Leo, that could indicate the presence of extraterrestrial life.

Using NASA’s James Webb Space Telescope (JWST), a British-US team led by Professor Nikku Madhusudhan of the University of Cambridge identified molecules in the planet’s atmosphere that, on Earth, are produced exclusively by living organisms.

While scientists urge caution, the findings are being hailed as a potential milestone in the search for life beyond Earth, said multiple media reports.

The research team reported the presence of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), chemicals associated with microbial life such as marine phytoplankton on Earth, in K2-18b’s atmosphere.

“This is the strongest evidence yet there is possibly life out there,” Madhusudhan told the BBC. He added, “I can realistically say that we can confirm this signal within one to two years.”

The concentrations of these molecules are reportedly thousands of times higher than those found on Earth, suggesting significant biological activity if the signals are confirmed. “If the association with life is real, then this planet will be teeming with life,” Madhusudhan said in an interview with The Independent.

The detection, made using JWST’s mid-infrared MIRI spectrograph, achieves a three-sigma statistical significance, indicating a 0.3 per cent chance the signal is a fluke.

However, the scientific community requires a five-sigma threshold for a definitive discovery. “It is in no one’s interest to claim prematurely that we have detected life,” Madhusudhan cautioned at a press conference, as reported by The New York Times.

A Hycean World with Oceans?

K2-18b, 2.6 times Earth’s radius and 8.6 times its mass, orbits a cool M-dwarf star in the habitable “Goldilocks” zone, where liquid water could exist. Previous JWST observations in 2023 detected methane and carbon dioxide, with a shortage of ammonia, supporting the hypothesis that K2-18b is a “Hycean” world — a planet with a hydrogen-rich atmosphere and a vast ocean.

“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,” Madhusudhan told Live Science.

However, not all scientists agree on K2-18b’s composition. Professor Oliver Shorttle of Cambridge University suggested the absence of ammonia could indicate an ocean of molten rock rather than liquid water, which would preclude life.

Similarly, Professor Raymond Pierrehumbert of Oxford University argued that K2-18b may be too hot for habitable water, with lava oceans more plausible. Others, like Professor Chris Lintott of BBC’s The Sky at Night, urged caution: “I think we’ve got to be very careful about claiming that this is ‘a moment’ in the search for life. We’ve had such moments before.”

Scientific Debate and Skepticism

The detection of DMS and DMDS has fueled vigorous debate. Edward Schwieterman, an astrobiologist at the University of California, Riverside, described the findings as “tentative,” noting that the signal could disappear upon reanalysis. Research published in 2024 by Nora Hänni of the University of Bern found DMS on a comet, suggesting non-biological processes could produce the molecule, casting doubt on its reliability as a biosignature.

Don Pollacco, a professor at the University of Warwick, told Newsweek: “We have little knowledge of what geological activities occur in these bodies and therefore if there are other routes to make this gas.”

Sara Seager of MIT warned that proving a biological origin for DMS could take decades due to the limited data from distant exoplanets. “The difficulty in proving that it couldn’t have a non-biological explanation could put K2-18b in the category of a viable biosignature candidate for a long time,” she told New Scientist.

Implications for the Search for Life

Despite the uncertainties, the findings are a testament to JWST’s unprecedented capabilities. “This is a revolutionary moment,” Madhusudhan told Newsweek. “It’s the first-time humanity has seen potential biosignatures on a habitable planet.” If confirmed, the discovery could suggest that life is common in the galaxy.

“If we confirm that there is life on K2-18b, it should basically confirm that life is very common in the galaxy,” Madhusudhan told BBC Radio 5Live.

The team plans further observations to achieve five-sigma significance and rule out non-biological explanations. “We hope to take these measurements soon, whenever we can get the JWST to look at this exoplanet for a few more hours,” Madhusudhan said, as reported by Live Science.

K2-18b and the Search for Exoplanet Life

K2-18b, also known as EPIC 201912552 b, was discovered in 2015 by NASA’s Kepler mission. It orbits the red dwarf star K2-18, a star 45 per cent the size of the Sun with a temperature of 3,457 K. The planet, classified as a sub-Neptune, has a 33-day orbit, a mass of 8.63 Earth masses, and a density suggesting a hydrogen-rich envelope. Its location in the habitable zone makes it a prime candidate for life.

In 2019, the Hubble Space Telescope detected water vapor in K2-18b’s atmosphere, sparking interest in its potential habitability. In 2023, JWST confirmed methane and carbon dioxide, with tentative hints of DMS, marking the first detection of carbon-based molecules in a habitable-zone exoplanet.

The 2025 study strengthens these findings with a more robust DMS and DMDS signal.

Challenges in Detection: Studying exoplanet atmospheres relies on analyzing starlight passing through their atmospheres during transits. This produces faint signals that are difficult to interpret. JWST’s advanced spectrographs have revolutionized this field, but the data’s complexity fuels debates over planetary composition and biosignatures.

NASA’s planned Habitable Worlds Observatory, set for launch in the 2040s, aims to detect biosignatures on Earth-like planets. Until then, JWST remains the best tool for studying worlds like K2-18b.

The proposed Confidence of Life Detection (CoLD) scale, with seven stages of increasing certainty, underscores the need for rigorous validation. K2-18b’s DMS detection is at CoLD Level 1, requiring further steps to confirm a biological origin.

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