Venus keeps teasing us about life

Scientists studying the atmosphere of Venus have found traces of a rare chemical that on Earth can only be produced by life. 

“So there is a chance that we have detected some kind of living organism in the clouds of Venus,” Jane Greaves, an astronomer at Cardiff University, UK, announced today at a press conference hosted by the Royal Astronomical Society.

Phosphine (PH₃) is a highly reactive gas that, on Earth, is only formed in significant quantities by certain types of anaerobic microorganisms. (It is also used as a fumigant.)

It was detected at levels of 20 parts per billion (ppb) – a finding, Greaves says, that was confirmed by two different radio telescopes, the James Clerk Maxwell telescope in Hawaii and the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile. 

Given the fact that these are independent observations, she says, her team has “very high confidence” that they actually detected the chemical.

To find it in the Venusian clouds, the astronomers examined radio emissions produced naturally in the lower Venus’s atmosphere as the planet radiates solar energy back into space. “Venus is a natural source of radio waves,” Greaves says.

As these radio waves pass upward through the clouds, a narrow bandwidth of them is absorbed by phosphine, leaving a distinctive spectroscopic signature. It is this signature that the astronomers were able to detect and confirm. 

What exactly this means is less certain. “We are not claiming we found life on Venus,” says Sara Seager of Massachusetts Institute of Technology (MIT), who was also part of the discovery team. Rather, says William Bains, also of MIT, “we are claiming there is something really unknown, and it might be life”.

Before making this claim, he says, the team put a great deal of effort into ruling out every possible non-biological source of phosphine that they or any of the study’s reviewers could think of. 

One option was that it might be formed by solar radiation high in the Venusian atmosphere, much the way that such radiation produces ozone in Earth’s upper atmosphere. But while some could be produced in that manner, Bains says, it was hundreds of thousands to millions of times too little.

The same goes for other types of atmospheric chemistry, and for emissions from volcanoes on the planet’s surface. 

“Yes, volcanoes could produce tiny traces, but it would be parts per quadrillion, not 20 parts per billion,” he says. 

And yes, atmospheric reactions from known or suspected components of Venus’s atmosphere can produce phosphine, but again, this couldn’t produce the amount of phosphine the astronomers had observed. It wasn’t “just ‘no’ but it was ‘no’ to many factors of 10″, he says.

Nor could it be explained by lightning or by meteorites containing some mineral that could break down into phosphine after they fell to the surface. Again, Bains says, such processes “fall short by factors of millions or more”.

That leaves only two possibilities, he says. Either there is some unknown, exotic phosphine-creating chemistry that nobody has so far thought of – or the phosphine is being produced by life.

The idea of life in the Venusian clouds isn’t new. It goes back several decades, and was initially proposed by Carl Sagan. 

These clouds lie in a “temperate zone” about 50-60 kilometres up, where the furnace-like heat and pressure of the lower atmosphere are sufficiently attenuated for liquid droplets to form. Life might have gotten there long ago, wafted up from the surface at a time when Venus was cooler and wetter than today. 

There is, however, one problem: the droplets in these clouds contain a lot of sulfuric acid: enough that anything living there would have to be adapted to survive in battery acid – or worse. 

“Sulfuric acid is terrible for all Earth life,” Seager says. “So it probably has to be completely different life. Our proteins and DNA would completely dissolve in those droplets.”

Nevertheless, she is excited about the find. “We have a growing number of Solar System bodies of astrobiological interest,” she says, naming Mars, Europa, Enceladus and Titan as four of particularly strong appeal. “Now, we have raised Venus higher up on the ladder of interesting targets.”

The research is published in a paper in the journal Nature Astronomy.

The Royal Institution of Australia has an Education resource based on this article. You can access it here.