Doubts Grow About the Biosignature Approach to Alien-Hunting

In 2020, scientists detected a gas called phosphine in the atmosphere of an Earth-size rocky planet. Knowing of no way that phosphine could be produced except through biological processes, “the scientists assert that something now alive is the only explanation for the chemical’s source,” the New York Times reported. As “biosignature gases” go, the phosphine seemed like a home run. Until it wasn’t.

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