For scientists, the urgent problem with phosphine—a molecule famously touted as a potential sign of life—isn’t so much about where it came from, but why it’s not where we think it should be. After a decade of searching, a long-awaited result has confirmed that our astronomical models aren’t a total bust. At least, for now.
In a Science paper published today, astronomers report the first-ever detection of strong phosphine signatures on a brown dwarf—a type of planet-star hybrid more massive than planets like Jupiter but not quite big enough to sustain the hydrogen fusion that powers stars. Prominent chemical models had long predicted that cosmic entities with gassy atmospheres would be rich in phosphine, but years of searching had turned up nearly nothing. The findings thus give closure to a problem that had plagued astronomers for at least a decade.
Just as importantly, the finding carries important implications for astrobiology. The phosphine detected on this brown dwarf, named Wolf 1130C, almost certainly formed through natural, abiotic processes. The challenge now is figuring out how an object like this could generate so much of it without life. Until researchers can explain that, any detection of phosphine—whether on a gas giant or a rocky planet like Venus—can’t be taken as a reliable sign of biology.
“The community has been waiting for this,” said Sara Seager, an MIT astrophysicist not involved in the new work. Seager co-authored a seminal paper from 2020 on the detection of phosphine on Venus. On Earth, phosphine mainly exists as the byproduct of anaerobic life, or creatures that thrive without oxygen. Because Venus’s chemical environment isn’t conducive to the natural formation of phosphine, the 2020 paper left astronomers wondering if the phosphine could have come from a life source—a biosignature.
“It is very refreshing—finally!” Nathalie Cabrol, research director at the SETI Institute’s Carl Sagan Center, added. Cabrol, also uninvolved in the new study, told Gizmodo in a video call that the paper presents “clear, plain” data of phosphine on the brown dwarf—just as models predicted.
A wild phosphine chase
Had the results come ten years ago, it wouldn’t have been this big of a deal, Adam Burgasser, study lead author and an astrophysicist at the University of California, San Diego, told Gizmodo. Chemical models had long supported the natural presence of phosphine on brown dwarfs or exoplanets with gassy atmospheres. That Jupiter and Saturn have phosphine-rich atmospheres also contributed to this assumption.
“It’s been a real weird problem, because it’s just this one molecule that seems to be a little bit out of sync.”
But after a decade of finding zero (or rather, several contested) signs of phosphine where models expected it to be, astronomers started to get rather skittish, explained Burgasser. In fact, astronomers had started to seriously consider substantially revising major models to account for the lack of phosphine.
“It’s been a real weird problem, because it’s just this one molecule that seems to be a little bit out of sync,” Burgasser said. “So, it’s actually a surprise that we have now finally detected it—in fact, detected it in abundance in this one particular brown dwarf.”
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