Suddenly, Venus was one of the most enticing targets in the search for life beyond Earth, and in those first moments, other scientists in the field were unusually excited about the research and its implications.
But in the months since the big announcement, the enthusiasm has dissipated. Other scientists have raised doubts about the research. The original team has revised its findings. The science community is divided—enough that one rebuttal paper had the authors “invite” the researchers who originally identified the phosphine to consider retracting their study altogether. In scientific literature, that counts as quite a salty attack, enough to make other researchers wince. (The researchers later removed that wording and apologized.)
Read: Why Venus is the best planet
The controversial part of this discovery was supposed to be the suggestion that life could exist in Venus’s clouds. Aliens, though, are not the subject of the current debate. Scientists are sparring over something more basic: the detection of the gas itself.
Is there phosphine in Venus’s atmosphere, or isn’t there? To a nonscientific observer, the question might seem straightforward enough. Why would determining this simple fact be complicated?
The shortest answer is that astronomy is hard. The work requires scientists to draw big conclusions about faraway places based on tiny signals imprinted on the light that reaches Earth. Telescope observations don’t produce handy readouts that say Yes phosphine or No phosphine. The scientists behind the discovery had to apply mathematical equations to extract those little signals from noisy data and then try to interpret them based on their current knowledge of another planet, which itself isn’t very robust. The momentous detection showed up in a simple plot of squiggly lines—or it didn’t, depending on whom you ask. Astronomy is full of disagreements like this one, but these squiggles provide the basis for nearly everything we know about the planets, stars, and galaxies beyond our own.
Venus was the first planet human beings ever explored with spacecraft. Starting in the 1960s, a series of Soviet missions revealed a furnace of a world, with a thick, cloudy atmosphere that keeps the surface so hot that lead would melt on it like ice on Earth. In the same era, astronomers Carl Sagan and Harold Morowitz suggested that, although Venusian ground was inhospitable to life, its atmosphere might not be. Perhaps the inhabitants of an early Venus, once as habitable and balmy as Earth, had escaped into the skies when the planet became unbearably sweltering.
Decades later, Jane Greaves, an astronomer at Cardiff University, directed a telescope at our next-door neighbor. Greaves had come across research that suggested astronomers looking for extraterrestrial life should consider checking for phosphine on exoplanets, since any alien astronomers looking back at us could likely spot signs of the same gas on Earth. She decided to test the idea on Venus. “I wasn’t really expecting that we’d detect anything,” Greaves told me in September.