Biosignature spotted on Venus could be volcanoes, not life

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A team of planetary scientists said that if there is phosphine on Venus, it may have geological rather than biological origins. Their findings suggest that phosphine, a chemical often associated with microbes, could come from a reaction in Venus’s sky caused by volcanic eruptions on the planet’s surface.

Last year, a scientific debate began when a team of scientists announced that they had discovered phosphine, a gas produced by some microorganisms, and thus considered a vital fingerprint, in the atmosphere of Venus. Other studies immediately complicated this finding, and earlier this year, another team said that the gas was not phosphine at all but sulfur dioxide. The team’s recent findings, published today in the Proceedings of the National Academy of Sciences, suggest that Venus could have active volcanoes, something planetary scientists have long been uncertain about.

The principle is: Venus’ deep mantle can contain phosphorous compounds, called phosphides, which can be belched into the atmosphere by the planet’s volcanoes in the form of volcanic dust. With enough explosive power—researchers described the force needed as that of Krakatoa on Earth or even the massive Yellowstone volcano—dust could explode high into the sulfuric acid-coated atmosphere. There, the phosphide reacts with sulfuric acid to produce phosphine.

A 1991 color radar image of a simulation of Maat Mons, a Venusian volcano, taken by the Magellan spacecraft. Photo: NASA/JPL

“Phosphenes do not tell us about the biology of Venus,” said Jonathan Lunin, a planetary scientist at Cornell University and co-author of the research paper, in a university press release. “It tells us about geology. Science refers to a planet with active eruptive volcanic activity today or in the very recent past.”

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But the mystery of whether or not Venus contains phosphine, and what might result from it, is far from settled. “Unfortunately I’m still not convinced by this last argument,” said Clara Souza Silva, a quantum astrochemist at the Center for Astrophysics. Harvard and Smithsonian, in an email. “The reaction of mineral phosphates with concentrated sulfuric acid will not necessarily produce phosphine. … The possible result of the reaction of phosphides with concentrated sulfuric acid would be an oxidation reaction and not the production of phosphine.”

Souza Silva’s previous work examined the atmospheres of Venus and other planets for possible signs of life such as phosphine. She added, “We’ve known (and said a lot, over and over again) that there are non-biotic ways to create phosphine, including volcanism. It’s just that these methods are extremely rare and ineffective.”

The tectonic movement of Venus is difficult to observe due to the dense atmosphere of the planet that hides its surface. The few images we have of the planet’s surface come from the Soviet Venera program in the 1970s and 1980s and radar scans from the Magellan Orbiter, which could penetrate Venus’ cloud cover. The data that Lunin’s team drew from their conclusions were collected using the James Clerk Maxwell Telescope on Mauna Kea and the ALMA telescope array in Chile. The researchers said that some of the images collected by Magellan indicated geological features capable of volcanic eruption. Previously, data from the European orbiter Venus Express indicated that the planet may contain active volcanoes.

Fortunately, three upcoming missions are set to tell us a lot about this hot planet. Around 2030, NASA’s DAVINCI+ probe, the VERITAS orbiter, and the European Space Agency’s EnVision orbiter will head to Venus to study atmospheric composition and surface tectonics, among other features of our nearest planet.

MORE: Why Venus Will Soon Be the Most Exciting Place in the Solar System

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