Potential Biosignatures Detected on Exoplanet K2-18b Using JWST

Astronomers have identified potential biosignatures in the atmosphere of exoplanet K2-18b, located approximately 124 light-years from Earth in the constellation Leo. Utilizing data from the James Webb Space Telescope (JWST), the research team, led by Professor Nikku Madhusudhan of the University of Cambridge, detected spectral features consistent with the presence of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS). On Earth, these compounds are predominantly produced by marine phytoplankton, suggesting a possible biological origin. The findings were published in The Astrophysical Journal Letters on April 17, 2025.

K2-18b is classified as a sub-Neptune exoplanet, with a radius approximately 2.6 times that of Earth and a mass about 8.6 times greater. It orbits within the habitable zone of its host star, a red dwarf, where conditions may allow for the presence of liquid water. Previous observations had detected methane and carbon dioxide in its atmosphere, further indicating potential habitability.

The detection of DMS and DMDS is intriguing because, on Earth, these compounds are primarily produced by marine phytoplankton, suggesting a possible biological origin. However, the researchers emphasize that these results are preliminary and require further validation. The statistical significance of the DMS detection is approximately 3 sigma, indicating a 0.3% probability that the signal is due to random noise. This falls short of the stringent threshold typically required for definitive scientific claims. Additionally, some scientists urge caution, noting the need for additional data to confirm the presence of these compounds and their biological origin.

The study underscores the capabilities of JWST in probing exoplanetary atmospheres and highlights the importance of continued observations to confirm potential biosignatures. Further research is needed to determine whether these chemical signatures indeed indicate biological activity on K2-18b or if alternative, non-biological processes could account for their presence.

Professor Nikku Madhusudhan is an Indian-British professor of astrophysics and Exoplanetary Science at the Institute of Astronomy, University of Cambridge. He is credited with developing an improved technique of atmospheric retrieval to infer the compositions of exoplanets and with coining the term “hycean planet” to describe a theorized class of planet that hosts a liquid water ocean beneath a hydrogen-rich atmosphere.

The potential detection of biosignatures on K2-18b has significant implications for the search for extraterrestrial life and our understanding of habitability beyond Earth. It challenges traditional notions of habitable environments and underscores the importance of considering diverse planetary conditions in the search for life. However, the controversy surrounding the premature hyping of uncertain science highlights concerns about overhyping uncertain science and its potential to erode public trust in future genuine discoveries.

While the detection of DMS and DMDS in the atmosphere of K2-18b is intriguing and represents a significant step forward in exoplanetary research, the findings are preliminary and require further validation. The scientific community remains cautiously optimistic, emphasizing the need for additional observations and rigorous analysis to confirm the presence and biological origin of these compounds.