Not finding life on Venus would be disappointing. But it’s good science at work

Repetition, repetition

The truth is, the story of Venus’s putative phosphine is not a simple case of a sensational finding being shot down upon further scrutiny. In fact, the rush of follow-up research is welcomed; science is doing its thing. This is especially true when it comes to the search for extraterrestrial life—after all, extraordinary claims require extraordinary evidence.

“I think this is a perfect example of how the scientific process works,” says Paul Byrne, a planetary scientist at North Carolina State University, who also wasn’t involved in the studies. “It certainly makes sense that there would be other studies that would try and get at this question.”

The first preprint paper to cast doubt on the original was actually written in part by Greaves herself. After failing to secure more time on telescopes to verify her team’s initial finding—the pandemic has made telescope access difficult and in some cases impossible—she and her colleagues turned to an archive of infrared observations made in 2015 and couldn’t find any sign of phosphine. 

This is frustrating, of course, but as Byrne says, “the absence of proof of a given detection is not proof of absence. It just might mean the problem is more complex than we’d like.” Maybe phosphine doesn’t actually exist on Venus, or maybe it varies over time. Or perhaps the archival observations Greaves analyzed didn’t probe deeply enough into the clouds. 

Replicability is actually a common problem when it comes to these kinds of investigations. Our current characterization of methane on Mars, for example, is under intense debate: NASA’s Curiosity rover has a has a history of detecting enormous spikes of methane on the planet, while ESA’s Trace Gas Orbiter, designed to study the gas on Mars with far more sensitive instruments than Curiosity, has found bupkis. The same goes for the detection of water plumes on Europa by the Hubble Space Telescope: subsequent investigations have struggled to find them.

Still processing

Another problem that plagues the phosphine findings is data processing. The two other preprints were written by teams that tried to reprocess the original data used by Greaves and her team, suspecting that the original analysis was flawed. It’s often a challenge to pull signals out of the massive amounts of noise found in telescopic data. Researchers in the original study used a technique called polynomial fitting, which is supposed to remove background noise around the spectral region where phosphine signals should pop up. But as National Geographic reports, the way they went about it might actually have introduced false phosphine signals. 

Both of these new preprints reprocessed the data from scratch, without using Greaves’s method. One focused solely on the ALMA data and failed to find phosphine. The other paper looked at both the ALMA and JCMT data. Researchers found no phosphine signal in the ALMA data and detected a signal in the JCMT set that might be explained by sulfur dioxide gas. 

Moreover, the ALMA observatory recently found an error in its calibration system used