But on smaller, rocky planets like Earth and Venus, the researchers say, there is not enough energy to produce copious amounts of phosphine in the same way. There is one thing, however, that appears to be very good at producing it: anaerobic life, or microbial organisms that don’t require or use oxygen.
On such worlds, “as far as we can tell, only life can make phosphine,” Dr. Sousa-Silva said. She has long studied the gas, on the theory that finding it being emitted from rocky planets that orbit distant stars could be proof that life exists elsewhere in the Milky Way.
Here on Earth, phosphine is found in our intestines, in the feces of badgers and penguins, and in some deep sea worms, as well as other biological environments associated with anaerobic organisms. It is also extremely poisonous. Militaries have employed it for chemical warfare, and it is used as a fumigant on farms. On the TV show “Breaking Bad,” the main character, Walter White, makes it to kill two rivals.
But scientists have yet to explain how Earth microbes make it.
“There’s not a lot of understanding of where it’s coming from, how it forms, things like that,” said Matthew Pasek, a geoscientist at the University of South Florida in Tampa. “We’ve seen it associated with where microbes are at, but we have not seen a microbe do it, which is a subtle difference, but an important one.”
Dr. Sousa-Silva was surprised when Dr. Greaves said that she had detected phosphine.
“That moment plays in my mind a lot, because I took a few minutes to consider what was happening,” she said.
If there really was phosphine on Venus, she believed there could be no other obvious explanation than anaerobic life.
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