SACHA PFEIFFER, HOST:
Venus is Earth's closest planetary neighbor, and now scientists have found a foul-smelling gas in its atmosphere that could indicate the presence of life, maybe microbes in the planet's hazy yellow clouds. NPR's Nell Greenfieldboyce reports that scientists are at a loss to explain what else could have produced this gas.
NELL GREENFIELDBOYCE, HOST:
The gas is called phosphine. Clara Sousa-Silva is an astrochemist at MIT. She says, to all oxygen-metabolizing life, which is most of life on Earth...
CLARA SOUSA-SILVA: It's an extremely dangerous molecule that kills in a variety of imaginative ways, all of which very final and macabre.
GREENFIELDBOYCE: This colorless gas has been used as a chemical warfare agent. And although not many people have smelled it and lived to tell the tale...
SOUSA-SILVA: Apparently it smells basically like death. It just smells horrific. We once, I think, found a report of someone saying it smelled like the rancid diapers of the spawn of Satan.
GREENFIELDBOYCE: And yet, weirdly, phosphine gas can be a sign of life because here on Earth, microbes make it - the kind of microbes that don't need oxygen, that live in swamps and sewage plants and intestines. Now, in the journal Nature Astronomy, researchers say they've detected phosphine in pretty substantial quantities in the clouds of Venus. Sousa-Silva says she and her colleagues racked their brains trying to come up with a possible source for it - obscure chemical reactions, lightning, meteorites.
SOUSA-SILVA: We have tried everything we can think of to explain the presence of phosphine through any avenue that isn't life, and we've run out of options.
GREENFIELDBOYCE: Folks like astronomer Carl Sagan actually talked about cloud life on Venus in the 1960s. While the planet's surface is a furnace - over 800 degrees Fahrenheit - conditions are more hospitable miles up in the sky. But more hospitable doesn't mean the clouds are cozy. Janusz Petkowski is a researcher at MIT.
JANUSZ PETKOWSKI: Clouds on Earth, these nice little puffy white things that float in the sky, are essentially water droplets. But on Venus, these cloud droplets are made of concentrated sulfuric acid.
GREENFIELDBOYCE: So could life really survive in such a hostile place?
PETKOWSKI: Personally, I think that it is very difficult to imagine, but it potentially could.
GREENFIELDBOYCE: And yet, when it comes to searching for life, instead of looking at Venus, many astrobiologists have focused on Mars and water-rich moons like Europa.
HILAIRY HARTNETT: Venus is like a giant unknown. Right? It's one of the planets that we almost know the least about in our own solar system.
GREENFIELDBOYCE: Hilairy Hartnett is a researcher at Arizona State University. She's thought a lot about phosphine as a possible sign of life on other worlds, like planets that orbit distant stars.
HARTNETT: This paper's kind of exciting because it's not just that they found it on another planet around another star. They have pretty compelling argument that they detected it on Venus. That's a big deal.
GREENFIELDBOYCE: It's in our backyard. A spacecraft could go check it out. Many scientists have already been clamoring for NASA to send a mission to Venus. This new finding will add more weight to their pleas. Bethany Ehlmann is a professor of planetary science at Caltech.
BETHANY EHLMANN: Phosphine means that there is something we don't understand about Venus (laughter). So that either relates to atmospheric chemistry, geology or geochemistry or life.
GREENFIELDBOYCE: She says life is the real attention-getter on that list. But as Carl Sagan said, extraordinary claims require extraordinary evidence.
Nell Greenfieldboyce, NPR News.
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