Yet, it wasn’t long until the team realized they’d made a mistake. In a re-analysis of their initial results released in November 2020, they announced that their new interpretation suggests significantly less phosphine in Venus’ atmosphere than they initially thought. However, they said, the signal was still there.
In the months since, other astronomers have been looking for evidence that might either confirm or refute this perplexing find. One team took additional observations with a telescope on Hawaii's Mauna Kea, but they couldn’t tease out a phosphine signature. Another team used data from old Venus probes, finding some hints of what might be phosphine. But ultimately, they couldn't confirm the original results.
Now, a group of researchers from the University of Washington say they’ve completed an exhaustive reanalysis of the phosphine signal. And they've concluded that it's probably not from phosphine at all.
These astronomers say that the original team made a mistake, and the observed signal is actually caused by sulfur dioxide — another gas that absorbs a similar wavelength of light as phosphine. Sulfur dioxide is a pungent gas that's familiar to us because it smells like burnt matches; but it’s not typically associated with life.
Life on Venus?
To reanalyze the initial team's results, the new team, which also included a number of NASA scientists, utilized a computer model of Venus’ atmosphere.
They plugged in decades of observations from ground-based telescopes and various spacecraft that have visited the world. Then, the researchers modeled the conditions and identified the various chemicals that would make their way into Venus’ thick atmosphere.
It's important to understand that every chemical absorbs wavelengths of light in their own unique way — giving it a specific
spectral signature. But sometimes, certain ones can be hard to distinguish from one another. The model let these latest researchers reanalyze the first team's initial spectral observations, and then compare those to what other instruments have detected over the years. Their results suggest the signal in question was not from phosphine, but instead sulfur dioxide. And that makes sense, considering sulfur dioxide is one of the most common chemicals found in the atmosphere of Venus.
The latest team also found that the signal most likely didn’t even come from the altitude the initial researchers thought; it came from much higher up in the mesosphere. The mesosphere exists some 50 miles (80 kilometers) above the planet’s surface, where the Sun’s radiation would almost instantly destroy highly fragile phosphine.
In fact, for that much phosphine to end up in Venus’ mesosphere, it would have to be injected at a rate roughly 100 times greater than photosynthesis delivers oxygen into Earth’s atmosphere.
So, does this rule out the idea that life could exist on Venus? Not hardly.
There’s still hope to hold on to, though, even if the phosphine signal isn’t real. Venus still has a Goldilocks temperature and pressure range found at certain altitudes. And just because there’s a reason to doubt the latest evidence of venusian life
doesn’t mean new evidence won’t emerge in the not-so-distant future.