Astronomers reported potential signs of life on the exoplanet K2-18b in April, but subsequent analysis has cast doubt on the findings. The initial excitement stemmed from a possible detection of dimethyl sulphide, a molecule linked to life on Earth. However, further observations confirm only methane and carbon dioxide in the planet's atmosphere.
In April, Nikku Madhusudhan from the University of Cambridge and his team shared observations from the James Webb Space Telescope (JWST) suggesting the presence of dimethyl sulphide (DMS) in the atmosphere of K2-18b. This exoplanet, located 124 light years away and orbiting within its star's habitable zone, is about eight times Earth's mass. On our planet, DMS is produced solely by living organisms, such as marine phytoplankton, sparking widespread interest in the scientific and media communities.
The detection was tentative, with experts immediately calling for more data due to the signal's weakness. Over the following months, additional JWST observations and analyses have led most astronomers to conclude that no DMS or similar biomolecule is present—or at least not detectable. Luis Welbanks of Arizona State University emphasized, “The only two things that we know for sure are that there is methane and carbon dioxide in the atmosphere of this planet.” He described the original claim as premature, noting that new data disproves the presence of those gases.
A lingering anomaly in the data, described as a 'bump' by Jake Taylor of the University of Oxford, remains unexplained. “There is this bump there. It’s physical. We see it. We just don’t know what the explanation is right now,” Taylor said. Further JWST observations are scheduled for next year, timed with the planet's transits across its star, which occur four times annually from Earth's perspective.
Despite the disappointment, the episode has benefited the field. Taylor highlighted it as a valuable learning process, prompting the exoplanet community to refine statistical methods and definitions. Welbanks added that it realigns expectations, cautioning against manipulating data to support claims and invoking the adage about 'lies, damned lies and statistics.'