Things may be moving on Venus’ surface.
In 1983, researchers discovered that the planet’s surface was speckled with strange, circular landforms. These rounded mountain belts, known as coronae, have no known Earthly counterparts, and they’ve remained enigmatic for decades. But hot plumes of rock upwelling from Venus’ mantle are shaping the mysterious landforms, a new analysis suggests. If true, that mean that Venus’ surface is tectonically active, and not merely a stagnant layer, researchers report May 14 in Science Advances.
Some “people have said, well, it’s geologically dead,” says earth and planetary scientist Anna Gülcher of the University of Bern in Switzerland. But over the past few years, there’s been a growing mound of evidence supporting tectonic activity on the Morning Star. The new work shows that “hot material resides beneath [coronae] and is likely driving tectonic processes that are not so different than what occurs on the Earth,” she says.
Gülcher and colleagues simulated how Venus’ crust deformed in response to material rising from the underlying mantle, a thick layer between the planet’s crust and core. This allowed the team to make predictions about what the underground plumes — buoyant blobs of hot material — and resulting coronae would look like to spacecraft instruments.
Then the team analyzed data on the planet’s topography and gravity collected in the early 1990s by NASA’s Magellan spacecraft, on the agency’s last mission to Venus. The gravity data were crucial. They revealed underground density differences linked to plumes rising from below.
By comparing the simulation predictions to the Magellan observations, the team was able to identify plumes beneath 52 of the observed coronae. What’s more, the simulation results suggested that the plumes had been sculpting the coronae in various ways.
One involves subduction, a process found on Earth where two tectonic plates collide, and one plunges under the other. On plateless Venus, subduction may be occurring along the periphery of the coronae, the researchers propose. As a column of material rises beneath a disk of crust, it will also bulge outward to the sides and push on the crustal flanges encircling the disk. If the crust is relatively strong, these flanges may bend downward and dive under the disk, subducting for much of a corona’s existence.
Earth’s subduction zones host the planet’s largest quakes, so if there are temblors on Venus, the strongest ones probably jolt at these coronal rims, Gülcher says.
Alternatively, if the crust is weak, a plume’s exertions may cause the surrounding flanges to detach and drip into Venus’ mantle, Gülcher says, “like honey.” And some coronae may form as upwelling plumes become embedded in the underlying crust or somewhere lower down, causing the crust above to swell. It’s sort of like a tectonic blister, says planetary scientist Paul Byrne of Washington University in St. Louis, who was not involved in the study.
The research supports the argument that Venus’ tectonics are active today, he says. What’s more, the demonstrated ability of computer simulations to predict what spacecraft may observe will be a boon to future Venus missions like the VERITAS mission, which will gather much higher resolution data than Magellan, Byrne says.
If Venus is tectonically active today, perhaps it could have been Earthlike in the past, Gülcher says. “Was there a period in Venus’ history that was … potentially less hot, and more habitable?”
