In a development that could reshape our understanding of life beyond Earth, scientists at the University of Cambridge have identified preliminary but compelling evidence suggesting that a distant exoplanet, K2-18b, might harbor life. Using NASA’s powerful James Webb Space Telescope (JWST), the team detected molecular signatures in the planet’s atmosphere that, on Earth, are only produced by living organisms.
K2-18b, located about 700 trillion miles from Earth, is more than twice the size of our planet. It orbits a small, cool red dwarf star, and it has long intrigued scientists due to its position in the so-called habitable zone, where temperatures might support liquid water. What makes this new finding stand out is the apparent presence of two life-related molecules: dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). Both are known on Earth to be byproducts of marine phytoplankton and certain bacteria.
This marks the second time such life-associated chemicals have been identified in the atmosphere of K2-18b by JWST, but the latest detection is considerably more promising, according to the researchers. The Cambridge team, led by Professor Nikku Madhusudhan at the university’s Institute of Astronomy, stresses that further observations are necessary before drawing firm conclusions. Still, Madhusudhan expressed cautious optimism.
“This is the strongest evidence yet there is possibly life out there,” he said. “I can realistically say that we can confirm this signal within one to two years.”
The James Webb Space Telescope, launched in 2021, is capable of analyzing the atmospheric composition of distant worlds by studying starlight that passes through their atmospheres. This allows scientists to identify the presence of various chemicals based on how the light is absorbed or altered.
According to Madhusudhan, the amount of DMS potentially found in K2-18b’s atmosphere during a single observation was unexpectedly high.
“The amount we estimate of this gas in the atmosphere is thousands of times higher than what we have on Earth,” he explained. “So, if the association with life is real, then this planet will be teeming with life.”
He went even further to suggest a broader implication: “If we confirm that there is life on K2-18b, it should basically confirm that life is very common in the galaxy.”
Despite the excitement, the scientific community remains cautious. The detection, while promising, has not yet reached the level of statistical confidence required for a formal discovery. Scientists typically require a five sigma result—equivalent to 99.99999% certainty—to claim a discovery. So far, the K2-18b finding stands at three sigma, or about 99.7% certainty. Although that is a significant improvement over the one sigma result of 68% obtained 18 months ago, it is still short of the rigorous threshold demanded in the field.
Independent experts echo this cautious stance. Professor Catherine Heymans of the University of Edinburgh, who also serves as Scotland’s Astronomer Royal, emphasized the complexity of interpreting such findings.
“Even with that certainty, there is still the question of what is the origin of this gas,” she told BBC News. “On Earth it is produced by microorganisms in the ocean, but even with perfect data we can’t say for sure that this is of a biological origin on an alien world because loads of strange things happen in the Universe and we don’t know what other geological activity could be happening on this planet that might produce the molecules.”
The Cambridge scientists are aligned with this view and are collaborating with other researchers to determine whether DMS and DMDS can be synthesized through non-biological processes in laboratory settings. These experiments aim to explore whether alternative, abiotic pathways could account for the detected molecules.
Some other research teams have already proposed non-biological explanations for the data obtained from JWST. One point of debate involves the absence of ammonia in K2-18b’s atmosphere. Some scientists argue that this suggests the presence of a vast liquid ocean capable of absorbing the ammonia, potentially creating a suitable environment for life. However, an equally plausible explanation is that the planet could have a molten rock ocean, which would be inhospitable to life.
“Everything we know about planets orbiting other stars comes from the tiny amounts of light that glance off their atmospheres,” said Professor Oliver Shorttle, also of Cambridge University. “So it is an incredibly tenuous signal that we are having to read, not only for signs of life, but everything else. With K2-18b part of the scientific debate is still about the structure of the planet.”
Meanwhile, Dr. Nicolas Wogan at NASA’s Ames Research Center has published research that interprets the data differently. According to his study, K2-18b might not be an ocean world at all but rather a mini gas giant with no solid surface, which would make the presence of life even more unlikely.
However, these alternate theories are not without their own challenges. Critics argue that some of the alternative models do not align with the JWST data. This has fueled an ongoing and vibrant scientific debate around the nature of K2-18b, its atmospheric composition, and its potential to support life.
Despite these uncertainties, Professor Madhusudhan remains hopeful and confident in his team’s approach.
“Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach,” he said. “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.”
The findings from the Cambridge team have been formally published in The Astrophysical Journal Letters, marking a significant milestone in the search for extraterrestrial life. While definitive proof remains elusive, the data from K2-18b brings scientists a step closer to understanding whether we are truly alone in the cosmos.