Scientists discovered minuscule levels of phosphine gas in the clouds of Venus last September, suggesting the intriguing possibility that alien bacteria are to blame.
Researchers have argued whether the gas is the result of biological, geological, or atmospheric activities since then.
They’ve even argued about whether or not it even existed in the first place.
If phosphine is present in Venus’s atmosphere, explosive volcanism could be to blame, according to a study published this week in Proceedings of the National Academy of Sciences.
Researchers determined that volcanic dust would need to be launched high into the Venusian atmosphere, where it would mix with sulfuric acid to generate phosphine, on the magnitude of Krakatau’s 1883 eruption on Earth—a devastating explosion in the Indonesian islands.
“Venus is a body that isn’t that much smaller than the Earth…but its geology is so different,” says Jonathan Lunine, chair of Cornell University’s astronomy department and a co-author of the study.
“The thought that volcanism is occurring on Venus right now…is a legitimate inference, and if it proves to be correct, it’s really exciting because it means that our nearest neighbor is geologically active right now.”
Because of its proximity and similar size and density, Venus is often referred to as Earth’s twin, and it may have formerly had oceans on its surface.
Today, the surface is hot enough to melt lead, the air pressure is 90 times that of Earth, and dense clouds of sulfuric acid blanket the sky.
Overall, this isn’t ideal real estate.
Nonetheless, when observatories in Hawaii and Chile identified the chemical signature of phosphine in Venus’s atmosphere, scientists wondered if it could be created by tough bacteria.
Other groups have questioned the findings, and the original team’s estimates of phosphine in Venus’s atmosphere have been lowered from roughly 20 parts per billion to between 1 and 5 parts per billion.
As a result, the topic of whether phosphine exists in Venus’s clouds remains unanswered.
Even if phosphine is present, scientists can’t agree on where it came from.
In their work on volcanism, Lunine and his coauthor Ngoc Truong, a doctorate candidate in geology at Cornell University, points out that there’s still a lot we don’t know about how bacteria make phosphine on Earth, let alone under the harsh conditions of Venus.
In any event, according to new research, there isn’t enough water in the Venusian clouds to sustain life.
Where might the phosphine have come from if not here? Volcanic eruptions are one possible explanation for the strange phosphine.
Magma carrying small amounts of compounds known as phosphides moves from deep within Venus’s mantle to the surface in this scenario.
The phosphides react with the surrounding sulfuric acid and are converted into phosphine after being expelled into the sky as volcanic dust.
Some scholars believe that a very high amount of volcanism would be required to achieve this.
Lunine and Truong, on the other hand, were not so confident.
They referenced many previously published research that demonstrated sulfuric acid converts phosphides to phosphine 1,000 times more efficiently than water.
This shows that the modest amounts of phosphides available from volcanic dust might form a significant amount of phosphine in Venus’s very acidic atmosphere.
The researchers then calculated how quickly the highly reactive phosphine gas would decay in the atmosphere (if it decayed too quickly, a telescope would miss it)
As well as the amounts of phosphide in the mantle and dust blasted into the atmosphere by volcanic eruptions that would be required to explain the telescope observations.
According to the experts, “major explosive volcanism” on the size of Krakatau’s eruption may transport material up to 70 kilometers (about 43.5 miles).
However, they have no idea how common or likely these incidents are.
Lunine adds, “We also point out that there is some circumstantial evidence for active volcanism on Venus now.”
Observations of a geologically recent lava flow on the planet’s surface, as well as periodic increases in sulfur dioxide, a chemical released by volcanoes, are among them.
“The most conceivable explanation for the phosphine being there, in our opinion, is ongoing volcanism on Venus,” Lunine explains.
“It appears that everything is in place for a reasonable quantity of volcanism.”
Scientists must now determine whether phosphine is present and whether Venus is still volcanically active, according to him.
Both NASA and the European Space Agency have missions to Venus planned in the next years, which could provide some answers.
“Venus provides an interesting opportunity to learn why Earth and Venus are so dissimilar,” says Truong.
“Venus is thrilling in and of itself, with or without life.”