JWST Unveils Potential Biosignatures on Exoplanet K2-18b

In a significant advancement in the search for extraterrestrial life, scientists have detected chemical compounds in the atmosphere of exoplanet K2-18b that, on Earth, are associated with biological activity. This discovery, made using the James Webb Space Telescope (JWST), brings researchers closer to understanding the potential habitability of distant worlds.

On April 16, 2025, a team led by Professor Nikku Madhusudhan from the University of Cambridge reported the detection of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of K2-18b. These findings were obtained using JWST's Mid-Infrared Instrument (MIRI). On Earth, DMS is predominantly produced by marine microorganisms, making its presence a potential biosignature. The researchers emphasize the need for further observations to confirm these detections and to rule out non-biological sources.

K2-18b is an exoplanet located approximately 124 light-years from Earth in the constellation Leo. It orbits the cool dwarf star K2-18 within the habitable zone, the region around a star where conditions might be right for liquid water to exist. The planet has a radius about 2.2 times that of Earth and a mass approximately 8.6 times greater. Its atmosphere is rich in hydrogen, and previous studies have suggested the presence of water vapor, methane, and carbon dioxide. These characteristics have led scientists to classify K2-18b as a potential "Hycean" world—a term coined by Professor Madhusudhan to describe exoplanets with hydrogen-rich atmospheres and global oceans, which could be conducive to life.

The recent study utilized JWST's MIRI to analyze the mid-infrared transmission spectrum of K2-18b. The data revealed spectral features consistent with the presence of DMS and DMDS. On Earth, DMS is primarily produced by marine phytoplankton and is considered a robust biosignature gas. The detection of these compounds in K2-18b's atmosphere suggests the possibility of biological activity. However, the researchers caution that the current evidence, while compelling, is not definitive. The statistical significance of the detections is around 3-sigma, indicating a need for further observations to confirm the findings and to explore potential abiotic sources of these compounds.

Professor Nikku Madhusudhan is a University Associate Professor in Astrophysics at the Institute of Astronomy, University of Cambridge. His research focuses on the atmospheres, interiors, and formation mechanisms of exoplanets. He is known for pioneering techniques to measure atmospheric properties of exoplanets and for introducing the concept of "Hycean" worlds. Professor Madhusudhan has received several accolades, including the EAS MERAC Prize in Theoretical Astrophysics in 2019 and the IUPAP Young Scientist Medal in Astrophysics in 2016.

The potential detection of DMS and DMDS in the atmosphere of K2-18b represents a significant advancement in the search for extraterrestrial life. If confirmed, these findings could indicate biological processes occurring on a planet beyond our solar system, challenging our understanding of life's distribution in the universe. The discovery also underscores the capabilities of JWST in probing exoplanetary atmospheres and identifying potential biosignatures.

However, the scientific community remains cautious. The current evidence does not meet the stringent statistical thresholds typically required for definitive claims of extraterrestrial life. Further observations and analyses are necessary to confirm the presence of these compounds and to rule out non-biological sources. Additionally, recent studies have suggested that DMS can be produced abiotically in cometary matter, indicating that its presence alone may not be a conclusive biosignature.

This is not the first time that potential biosignatures have been reported in the atmosphere of K2-18b. In 2023, researchers detected methane and carbon dioxide, and there was a tentative indication of DMS. The current study builds upon these findings with more robust data from JWST, providing stronger evidence for the presence of DMS and DMDS. However, as with previous studies, the results are preliminary and require further validation.

In conclusion, the detection of potential biosignatures on K2-18b is a compelling development in the field of exoplanetary science. While the findings are promising, they also highlight the complexities and challenges inherent in the search for life beyond Earth.