How one planet is revealing why it’s so hard to detect life beyond Earth

(CNN) — A tiny sign revealed in April seemed like it might change the universe as we know it.

Astronomers had detected just a hint, a glimmer of two molecules swirling in the atmosphere of a distant planet called K2-18b — molecules that on Earth are produced only by living things. It was a tantalizing prospect: the most promising evidence yet of an extraterrestrial biosignature, or traces of life linked to biological activity.

But only weeks later, new findings suggest the search must continue.

“It was exciting, but it immediately raised several red flags because that claim of a potential biosignature would be historic, but also the significance or the strength of the statistical evidence seemed to be too high for the data,” said Dr. Luis Welbanks, a postdoctoral research scholar at