Venus Isn't (Geologically) Dead

Scientific American

14-05-2025

Earth's geology is downright vital. Here, giant 'plates' of the crust rift apart and smash together like pieces of an ever changing planetary jigsaw puzzle. Mountains rise, volcanoes spew, and Earth itself quakes as the crust constantly remakes itself in the ceaseless cycle of plate tectonics. This is a process that controls the flow of carbon through our planet and stabilizes its climate; were it not for plate tectonics, Earth might not be habitable at all.
No other rocky world in our solar system has anything approaching Earth's degree of geological activity. At least, that's what scientists used to think. Mercury, Mars and the moon appear essentially inert. But Venus, our closest neighbor and the only other large rocky world around the sun, is now starting to look far livelier than once thought. A fresh look at decades-old data from NASA's Magellan probe has found evidence of active tectonics—around dozens of circular volcanic features called coronae—on Venus today. The finding, published on Wednesday in Science Advances, provides some of the best evidence to date that Venus isn't dead—at least, not when it comes to tectonics.
'Venus works differently than the Earth but not as different as what was originally assumed,' says the study's co-lead author Anna Gülcher of the University of Bern in Switzerland. 'We should think of tectonics as not just a black-and-white picture.'
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'Questions as fundamental as 'Is Venus alive today?' are extremely hard to answer,' says planetary scientist Paul Byrne of the University of Washington in St. Louis, who wasn't involved in the study. This new evidence of geological activity around the coronae suggests 'the heart of Venus still beats today. I think that's extremely invaluable for us to understand the big, rocky world next door.'
Venus is called ' Earth's evil twin ' for good reason: the planet is almost exactly as large as the Earth and is made of roughly the same stuff. But while Earth is a verdant water world, Venus is a scorched hellscape with temperatures hot enough to melt lead, a dreary, permanently overcast sky and air so thick that it crushes spacecraft as if they were tin cans.
For a while, Venus was widely assumed to be just as dead on the inside as it is on the outside. Lacking any obvious plate tectonics—which can help release a world's internal heat—Venus's interior was thought to instead just simmer like the contents of a tight-lidded pot on a stove. According to one popular hypothesis, the pot had eventually boiled over: after eons of frustrated heating, some 800 million years ago, the planet's outer shell buckled, and Venus's entire surface was paved over with immense outpourings of fresh lava. And, the thinking went, with all that heat dissipated, the planet's geology basically shut down.
But evidence is mounting that Venus is, geologically at least, still kicking. Most notably, in 2023 two researchers scrutinizing 30-year-old Magellan data realized that the probe had caught a volcanic eruption in the act: radar images of the volcano Maat Mons that were taken months apart showed what looked like a caldera collapse and subsequent lava flow. Venus, it seems, still has active volcanoes. Some researchers now think it could have active tectonics, too. And in 2020 Gülcher and her colleagues showed via simulations of Venusian tectonics that the planet's mysterious, ring-shaped coronae could be a good place to look for such activity.
Tectonics refers to the processes that deform a rocky planet's brittle outer shell. On Earth, this outer shell—the lithosphere, which includes the crust and part of the upper mantle—is broken into tectonic plates that drift over the hot, plastic mantle. When two plates collide, one of them can slide below the other and dive down into the mantle in a process called subduction. On Earth, subducting plates start melting as they sink, feeding volcanoes along plate boundaries. Such volcanoes include Japan's Mount Fuji and western North America's Cascade Range.
Unlike Earth, Venus doesn't have global plate tectonics. The new study suggests, however, that around coronae, something quite similar to subduction could be happening.
Gülcher and her colleagues simulated several tectonic processes that might be occurring around coronae and compared their predictions to real observations collected by the Magellan probe 30 years ago. The comparisons were more than skin-deep: the researchers used gravity data to take a peek underground. Hot rock is generally less dense than cold rock, and these density variations from place to place can correspondingly alter the strength of a planet's gravitational field. So Magellan's spatial mapping of Venus's gravity can 'see' if there's hot, light material under a corona—a sign that rock is actively rising up from the mantle below.
Of the 75 coronae that the team could resolve in Magellan's gravitational maps, 52 seem to be geologically active. The predicted and real data lined up so well for some coronae that 'we could hardly believe our eyes,' says the study's other co-lead author Gael Cascioli of NASA's Goddard Space Flight Center and the University of Maryland, Baltimore County. Most of the active coronae were encircled by trenches, a hint that old crust dives into Venus's mantle around these rocky rings, where it is driven downward as buoyant rock rises from below in the middle of each corona's ring structure. 'Basically, if something goes down, something goes up,' Gülcher says. Where the lithosphere is softer and more pliable, bits of it could break off and 'drip' down into the mantle in globs. In places where the lithosphere is stiffer, entire slabs of crust could subduct in a small-scale, circular mirror of Earth's subduction zones, like those that form the Pacific Ocean's famed volcanic Ring of Fire.
Working with 30-year-old data comes with an obvious limitation: the data quality often isn't very good compared with newer observations. The new study's researchers did well with what they had, Byrne says. But NASA's upcoming VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) mission could do much better—and the team predicted exactly how much better in the paper. 'The improvement would be extraordinary,' Cascioli says. Instead of being limited to analyzing 75 coronae, VERITAS's gravity dataset should allow scientists to examine hundreds of the strange ring-shaped features.
For the foreseeable future, Venus is the only other large, rocky world that we or our robotic emissaries will ever reach. Understanding why Earth and Venus ended up so different despite having so much in common helps us understand our own planet—and whether the rocky worlds we're beginning to glimpse around other stars are more like Earth or instead resemble its evil twin.
'Venus is the world that we probably understand least,' Byrne says. 'Yet it's the one, arguably, I think, that's the most important.'