A team of planetary scientists said that if there is phosphine on Venus, it could have geological—not biological—origins. Their findings suggest that phosphine, a chemical often associated with microbes, could come from a reaction in the Venusian sky kicked off by volcanic eruptions on the planet’s surface.
Last year, a scientific debate began when a team of scientists announced they had detected phosphine, a gas that is produced by some microorganisms and thus considered a biosignature, in Venus’s atmosphere. Further studies immediately complicated that result, and earlier this year another team said the gas wasn’t phosphine at all but sulfur dioxide. The recent team’s findings, published today in the Proceedings of the National Academy of Sciences, indicate that Venus could have active volcanoes, something planetary scientists have long been unsure about.
The principle is this: Venus’s deep mantle could contain phosphorus compounds, called phosphides, which could be belched into the atmosphere by the planet’s volcanoes in the form of volcanic dust. With enough explosive force—the researchers described the necessary force as that of Earth’s Krakatoa or even the Yellowstone supervolcano—that dust could be blasted high into the planet’s sulfuric acid-clouded atmosphere. There, the phosphides would react with the sulfuric acid to produce phosphine.
“The phosphine is not telling us about the biology of Venus,” said Jonathan Lunine, a planetary scientist at Cornell University and co-author of the paper, in a university press release. “It’s telling us about the geology. Science is pointing to a planet that has active explosive volcanism today or in the very recent past.”
But the mystery of whether Venus has phosphine or not, and what might have produced it, is far from settled. “I sadly remain unconvinced by this latest argument,” said Clara Sousa-Silva, a quantum astrochemist at the Center for Astrophysics | Harvard and Smithsonian, in an email. “The reaction of mineral phosphides with concentrated sulfuric acid will not necessarily generate phosphine. ... A likely outcome of reacting phosphides with concentrated sulfuric acid would be an oxidation reaction and not production of phosphine.”
Sousa-Silva’s previous work has examined the atmospheres of Venus and other planets for potential signs of life like phosphine. She added, “we have known (and stated as much, repeatedly) that there are abiotic routes for the formation of phosphine, including volcanism. It’s just that these routes are extremely rare and inefficient.”
Venus’s tectonics are difficult to observe because of the planet’s dense atmosphere, which conceals its surface. The few images we have of the planet’s surface come from the Soviet Venera program of the 1970s and 80s and radar scans taken by the Magellan Orbiter, which can pierce through Venus’s cloud cover. The data that Lunine’s team drew their conclusions from was collected using the James Clerk Maxwell Telescope on Mauna Kea and the ALMA telescope array in Chile. Some images collected by Magellan indicated geological features capable of explosive volcanism, the researchers said. Previously, data from Europe’s Venus Express orbiter indicated that the planet may have active volcanoes.
Thankfully, three upcoming missions are set to tell us a whole lot more about this scorching-hot planet. Around 2030, NASA’s DAVINCI+ probe and VERITAS orbiter and the European Space Agency’s EnVision orbiter will all head to Venus to study its atmospheric makeup and surface tectonics, among other features of our nearest planetary neighbor.