Active volcano on Venus shows it’s a living planet

2023-03-15

Choked by a smog of sulfuric acid and scorched by temperatures hot enough to melt lead, the surface of Venus is sure to be lifeless. For decades, researchers also thought the planet itself was dead, capped by a thick, stagnant lid of crust and unaltered by active rifts or volcanoes. But hints of volcanism have mounted recently, and now comes the best one yet: direct evidence for an eruption. Geologically, at least, Venus is alive.

The discovery comes from NASA’s Magellan spacecraft, which orbited Venus some 30 years ago and used radar to peer through the thick clouds. Images made 8 months apart show a volcano’s circular mouth, or caldera, growing dramatically in a sudden collapse. On Earth, such collapses occur when magma that had supported the caldera vents or drains away, as happened during a 2018 eruption at Hawaii’s Kilauea volcano. “I’m totally tickled, as a geomorphologist, to see this,” says Martha Gilmore, a planetary scientist at Wesleyan University who was not involved in the study.

Witnessing this unrest during the short observation period suggests either Magellan was spectacularly lucky, or, like Earth, Venus has many volcanoes spouting off regularly, says Robert Herrick, a planetary scientist at the University of Alaska, Fairbanks. Herrick, who led the study, says, “We can rule out that it’s a dying planet.”

The discovery, published today in Science and presented at the Lunar and Planetary Science Conference, makes Venus only the third planetary body in the Solar System with active magma volcanoes, joining Earth and Io, Jupiter’s fiery moon. It means future missions to Venus will be able to study “bare, gorgeous new rock” that provides a sample of the planet’s interior, Gilmore says. The discovery of more volcanoes, in old or future data, will also help scientists understand how Venus is shedding its interior heat and evolving. And it will shake scientists out of their long-standing view that a spasm of activity a half-billion years ago repaved the planet’s surface—as evidenced by a relative paucity of impact craters—and was followed by a long period of quiet. “We’ve all had our stagnant-lid lenses on to understand the planet,” says Suzanne Smrekar, a planetary scientist at NASA’s Jet Propulsion Laboratory (JPL). “We’re finally getting an eye correction.”

Recent years had brought hints that Venus has some geologic life. In 2010, researchers on the European Space Agency’s Venus Express mission detected three anomalously hot regions, which they interpreted as lava flows a few million years old that hadn’t yet cooled off. A couple of years later, the spacecraft found atmospheric spikes of sulfur dioxide, suggesting it was supplied by a variable source, such as volcanoes. And in 2021, a reanalysis of Magellan data indicated large blocks of crust had been jostled around like pack ice—a sign of rock stirring below the surface.

Prompted by these hints, Herrick decided to take another look at the Magellan data. “It’s essentially looking for a needle in a haystack with no guarantee there’s a needle there,” he says. He targeted obvious candidates, such as Maat Mons, a volcano taller than Mount Everest. Magellan had already found that the force of gravity above it was surprisingly low—a sign that a hot plume of less-dense rock from the mantle might be fueling it, like the plume that sits beneath Hawaii. And microwave radiation from the summit suggested its surface had the chemistry of fresh lava.

Herrick had an unlikely ally in his search: endless pandemic Zoom meetings, which gave him time to compare radar images made at different times. “If anyone asks about a specific meeting, I was fully attentive at that one,” he jokes.

The hunt was hard. At a resolution of several hundred meters, Magellan images are relatively coarse, only sensitive to the biggest changes in the landscape. Moreover, during its 5-year mission, the spacecraft revisited the same spots at most three times, and during its second campaign, its radar had been rotated 180°. Comparing ground features from opposite angles is far from intuitive, Herrick says. “The same things look quite different.”

But after hundreds of hours of tedious comparisons, covering less than 2% of the venusian surface, Herrick spotted what looked like a changed caldera. To avoid being fooled, he contacted Scott Hensley, a radar specialist at JPL well-known for debunking past false alarms in Magellan data. Hensley modeled what an unchanged caldera should have looked like during the second Magellan pass—starkly different from what was observed. The second image also appeared to show fresh lava flows, but those could have been hidden from view during the first pass, Herrick cautions. Still, the caldera changes are unequivocal evidence of volcanic activity, Smrekar says.

The discovery is just a preview of what is likely to come with three new Venus missions due to launch in the next decade: the European EnVision orbiter and NASA’s DAVINCI and VERITAS missions. Both EnVision and VERITAS will be equipped with sharper radar vision than Magellan, making them well suited to monitoring the burps and twitches of a living planet, Herrick says. “We’re guaranteed to see some really big changes.”

Science, 15 March 2023
; https://science.org