The original version of this story appeared in Quanta Magazine.
In 2020, scientists detected a gas called phosphine in the atmosphere of an Earth-sized 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.
The planet was Venus, and the claim about a potential biosignature in the Venusian sky is still mired in controversy, even years later. Scientists can’t agree on whether phosphine is even present there, let alone whether it would be
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