‘We may not be alone’: James Webb discovers possible alien life on planet K2-18 b

In what could mark a pivotal moment in the search for extraterrestrial life, scientists using the James Webb Space Telescope have detected what they describe as the strongest evidence yet of potential biology beyond Earth.

Observations of a distant exoplanet named K2-18 b revealed atmospheric traces of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS)—gases on Earth produced exclusively by living organisms, primarily marine microbes such as phytoplankton.

The findings, detailed in a study led by astrophysicist Nikku Madhusudhan of the University of Cambridge's Institute of Astronomy, have stirred cautious excitement. “This is a transformational moment in the search for life beyond the solar system, where we have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities,” Madhusudhan said. “We have entered the era of observational astrobiology.”

K2-18 b, located 124 light-years away in the constellation Leo, is roughly 8.6 times as massive as Earth and orbits within the "habitable zone" of a red dwarf star—where liquid water could theoretically exist. The planet is classified as a "hycean world," a theorized type of exoplanet with hydrogen-rich atmospheres and oceans potentially habitable by microorganisms.

Earlier Webb observations had already identified methane and carbon dioxide on K2-18 b. The latest data builds on that, suggesting the presence of DMS or DMDS at concentrations over 10 parts per million—thousands of times higher than on Earth. “This cannot be explained without biological activity based on existing knowledge,” Madhusudhan noted.

Still, he cautioned against jumping to conclusions. “We need to repeat the observations two to three times to make sure the signal we are seeing is robust and to increase the detection significance,” he said. Further studies will also explore whether these gases might be produced by non-biological processes in a planetary atmosphere like that of K2-18 b.

Madhusudhan emphasized, “It is in no one’s interest to claim prematurely that we have detected life.”

Using the transit method, Webb observed starlight passing through the planet’s atmosphere as K2-18 b crossed its host star. This allowed scientists to analyze its chemical composition. A previous hint of DMS from Webb was now reinforced using a different instrument and light wavelength.

Though the possibility of microbial life in a clean world is compelling, other scientists urged patience. “These latest data are a valuable contribution to our understanding,” said Christopher Glein of the Southwest Research Institute. “Yet, we must be very careful to test the data as thoroughly as possible.”

(With Reuters inputs)