A team of international astronomers has announced the detection of the most promising signs yet of possible life on an exoplanet outside our Solar System: K2-18b. Located 124 light-years from Earth in the constellation Leo, K2-18b has been a focal point of scientific debate due to its potential ability to host microbial life. Often referred to as a "hycean planet," it resides in the habitable zone of its star—a region where temperatures are suitable for the existence of liquid water.
Using the James Webb Space Telescope (JWST), researchers identified two chemical compounds in the atmosphere of K2-18b that are considered biosignatures—indicators of life. These compounds, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), are produced exclusively by living organisms on Earth, such as marine phytoplankton. This breakthrough follows the JWST's earlier detection of methane and carbon dioxide in K2-18b's atmosphere in 2023.
“For now, what we have are signs of possible biological activity outside the Solar System,” said Nikku Madhusudhan, an astrophysicist at the University of Cambridge and the lead author of the study published in The Astrophysical Journal Letters. “Frankly, I believe this is the closest we have ever been to observing a characteristic that we can attribute to life.”
While the findings are exciting, scientists caution that more observations are necessary to confirm the existence of life on K2-18b. Madhusudhan noted, “The concentration of DMS observed in K2-18b appears to be thousands of times stronger than that found on Earth, strongly suggesting a biological origin.” However, he also emphasized that the presence of these compounds does not definitively mean that life exists there, as DMS has been found in comets, indicating it could also be produced by non-organic processes.
K2-18b, which has more than eight times the mass of Earth and is 2.5 times larger, orbits its star every 33 days. Astronomers can determine the composition of an exoplanet's atmosphere when it passes in front of its star, allowing them to conduct spectroscopy on the light that filters through its gaseous layer. This method was employed by Madhusudhan and his team during their observations in 2024, utilizing the JWST's medium-infrared instruments to detect different wavelengths of light.
The concept of K2-18b as a hycean planet has been a topic of interest since its discovery in 2017. Madhusudhan and his colleagues proposed that sub-Neptune planets like K2-18b could be covered by warm oceans and surrounded by hydrogen-rich atmospheres. However, there remains some skepticism among scientists regarding the planet's capacity to support life. Raymond Pierrehumbert, a professor of planetary physics at the University of Oxford, has suggested that K2-18b may be too hot to harbor life, positing that it could contain lava oceans instead of liquid water.
In the wake of the latest findings, Madhusudhan estimated that only an additional 16 to 24 hours of observations by the JWST would be needed to confirm their discoveries, a process that could unfold in the coming years. “If we confirm that there is life on K2-18b, it would basically confirm that life is quite common in the galaxy,” he asserted.
In a related study published on April 16, 2025, researchers from the University of Cambridge revealed that the atmosphere of K2-18b contains the chemical signature of DMS and DMDS, molecules that, on Earth, are produced solely by living organisms. This research, which has stirred excitement within the astronomical community, emphasizes that while the evidence is compelling, it is not definitive proof of extraterrestrial life.
“This is a revolutionary moment. It is the first time humanity has seen potential biosignatures on a habitable planet,” Madhusudhan remarked. He acknowledged, however, that it is premature to claim that life has been detected. “We need more data to confirm these findings,” he added.
The K2-18b exoplanet was initially discovered by Canadian scientists in 2015. Since then, it has garnered significant attention due to its location in the habitable zone and the potential for liquid water. In 2019, the first indications of water vapor were detected on the planet, further bolstering the hypothesis that K2-18b could be covered by oceans.
Despite the enthusiasm surrounding the discovery of DMS and DMDS, scientists are careful to temper expectations. The recent findings are based on preliminary data, and the current level of certainty is about 99.7%. For results to be considered conclusive, researchers typically aim for a confidence level of five sigma, which corresponds to 99.99999% certainty.
Even if future observations confirm the presence of these molecules, it would not definitively prove the existence of life. Catherine Heymans, an astronomer at the University of Edinburgh, pointed out that while DMS is associated with life on Earth, its presence on another planet does not guarantee a biological origin. “Strange things happen in the universe, and we cannot rule out other geological processes that might produce these molecules,” she stated.
As the scientific community continues to debate the implications of these findings, Madhusudhan remains optimistic about the future of astrobiological research. “In a few decades, we might look back at this moment and recognize it as the time when the living universe became something within our reach,” he concluded. “This could be the turning point where we can finally answer the fundamental question: are we alone in the universe?”
