The James Webb Space Telescope has produced its most extraordinary finding yet: the detection of dimethyl sulphide (DMS) in the atmosphere of K2-18b — a "Hycean world" 120 light-years from Earth — a molecule that, on Earth, is produced exclusively by living organisms, primarily marine phytoplankton.
The discovery, published in Nature Astronomy, is being described by astrobiologists as "the most significant potential evidence for extraterrestrial life in the history of astronomy." Scientists are careful to note that the finding is not confirmation of life — alternative non-biological production pathways for DMS cannot yet be ruled out with current data — but the signal is statistically robust and has withstood rigorous peer review.
What Is K2-18b?
K2-18b is a "sub-Neptune" or "Hycean" world — a class of exoplanet theorised to have vast liquid water oceans beneath hydrogen-rich atmospheres, potentially habitable to microbial life. The planet orbits its star in the "habitable zone" — the distance at which liquid water can exist on a planetary surface.