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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 t

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