British scientists have captured clues suggesting the possibility of life on the exoplanet "K2-18b." However, some in the scientific community caution against premature interpretations, stating that more careful verification is necessary.
Researchers at the University of Cambridge announced on the 17th (local time) that they have detected signals of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of the exoplanet K2-18b, located 124 light-years away from Earth, using the James Webb Space Telescope (JWST). These molecules are substances generated by phytoplankton in Earth's oceans.
Discovered in 2015, K2-18b is approximately 8 times heavier than Earth. Although it is closer to a gas giant like Neptune than to a rocky planet like Earth, it is located in a habitable zone where water can exist in liquid form. Liquid water is the most critical requirement for the existence of life. If a planet is too close to its star, water evaporates, while if it is too far, water freezes.
In 2019, the detection of water vapor traces in the atmosphere of this planet raised the possibility of a water-rich atmosphere and hydrogen-rich environment, and in 2023, signals of DMS molecules were observed following the detection of water vapor, carbon dioxide, and methane by JWST. This time, signals of DMDS, a molecule generated only by living organisms, have also been captured using different observational equipment from JWST.
Niku Madhusudhan, a professor at the University of Cambridge, said at a press conference held on the 15th that "this is likely the first clue about an alien world where humans could potentially reside," adding that it is "independent evidence suggesting the possibility of biological activity on Earth."
The research team explained that this signal has a statistical significance of 3 sigma. This means that the probability of it being a mere coincidence is around 0.3%, similar to the chance of getting the same result 10 times when flipping a coin.
However, it still falls short of the 5 sigma level required for a new discovery in the scientific community. A 5 sigma result means that the probability of the data occurring by chance is 1 in 3.5 million, akin to the probability of getting the same result when flipping a coin 20 times in a row.
Nicolas Wargon, a postdoctoral researcher at the NASA Ames Research Center, noted, "This is a more compelling result than the 2023 findings, but it still needs to be verified by other research teams." Ryan McDonald, a professor at the University of Michigan, emphasized that "there were signals at the 3 sigma level from K2-18b before, but most disappeared under subsequent reviews," noting that "claims of this kind need rigorous verification from other scientists."
There remains the possibility that the detected signal is influenced by observational equipment or that DMS and DMDS may have been generated through abiological processes. An international research team led by the University of Bern in Switzerland reported last November that although DMS is present in comets explored by the European Space Agency (ESA), it is clear that no life exists there.
In response to critical views from the scientific community, the researchers at the University of Cambridge estimated that they could reach the 5 sigma level with an additional 16 to 24 hours of observation. Thomas Beatty, a professor at the University of Wisconsin-Madison, said, "The relative size of the atmosphere compared to the planet's size is almost like the thickness of an apple peel, which could make accurate measurements difficult," but added, "If it can be verified through additional observations, it would be a tremendous advancement."
References
The Astrophysical Journal Letters (2025), DOI: https://doi.org/10.3847/2041-8213/adc1c8