It turns out that Venus (almost) has tectonic plates


Beneath Venus’s acidic clouds and crushing atmospheric pressure lies a rocky surface strewn with geological mysteries.

Sometimes referred to as Earth’s “sister planet” because it is similar in size with a similar iron core, molten mantle, and rocky crust, there is evidence that Venus was once a aquatic world like ours, and maybe even had life (or maybe not). But now it’s a hellish landscape at 900 degrees Fahrenheit in an atmosphere suffocated by carbon dioxide and sulfuric acid.

Scientists are really curious as to how this happened and if it has anything to do with the fact that the volcanic plains covering most of the surface are relatively free from impact craters, as if they were formed there is only a few hundred million years old. And since volcanoes are usually tied to tectonic activity, scientists are very keen to understand how the latter worked on Venus – or maybe it still works.

Now, a new look at images from nearly 30 years of the surface of Venus from the Magellan mission revealed that Venus’ outer crust is shattered into a bunch of small, plate-like pieces. They are not quite tectonic plates as we know them on Earth, but they suggest that “Venus is much more dynamic and much more interesting than we might have thought a few decades ago.” says Paul Byrne, planetary geologist at North Carolina State University and co-author of study describing the fragmented crust of Venus. Planetologists are eager for new data from the upcoming VERITAS and EnVision missions to give them a better view of the planet and its geological activity.

A 1,100 km wide false-color radar view of Lavinia Planitia, one of the Venus Plain regions where the lithosphere has fragmented into blocks (purple) bounded by belts of tectonic structures (yellow). (Credit: NC State University, based on original NASA / JPL images.)

Like we need another reason why Venus is strange

The earth’s crust is divided into seven major and eight minor tectonic plates which are in constant motion relative to each other. The movement is driven, at least in part, by convection in the mantle. The internal heat flow in the mantle causes it to spin slowly, much like a lava lamp, and some of the churning motion is transferred to the plates.

The prevailing opinion among planetary scientists since Magellan has been that Venus’ crust behaves more like that of Mars – rigid and immobile – than that of Earth, and has been so for at least half a billion years. years. But new analysis, including the work of Byrne, suggests that Venus, true to its penchant for strangeness, behaves differently from Mars or Earth (or at least millions of years ago).

Magellan’s radar mapped 98% of Venus’ surface between 1990 and 1992. The images show that the flat volcanic plains that cover over 80% of the planet are streaked with ridges and grooves – evidence of pushing, pulling and geological scrapings that must have occurred one day. after laying the lava fields.

Byrne and his colleagues noticed that the ridges seemed to describe distinct chunks. They identified 58 clearly defined boulders of crust in the lowlands of the planet, the largest of which is roughly the size of Alaska. Some blocks appear to be connected. Laurent Montesi, a planetary geologist at the University of Maryland who was not involved in the study, says he wouldn’t be surprised if there was a network of them spanning the entire planet.

When tectonic plates on Earth collide, one will be pushed under the other in a process called subduction. There is no evidence of subduction on Venus, which is why it cannot really be said to have tectonic plates. What he seems to have, Montesi says, are “stiff fragments in a sea of ​​pasty stuff that allow them to jostle each other,” pushed by the inner movement of the mantle. When they collided with each other, the blocks crumpled at the edges to raise the ridges that surrounded them.

Don’t stop moving just because we’re watching now

The big question is whether Venus’s crust is still moving or whether it stopped millions of years ago. The answer to this question will have major implications for scientists’ understanding of the evolution of Venus in the strange world we now know. Did it resurface more or less suddenly by a great volcanic cataclysm a few hundred million years ago, or is it a more progressive and perhaps still ongoing series of events? smaller shaped the planet?

It is really difficult to answer such questions without rock samples or seismic data, explains Joann Stock, a structural geologist at Caltech and a member of the scientific team at VERITAS. Unfortunately, there isn’t a technology yet that can withstand the corrosive atmosphere and surface temperatures it would take to put a rover on Venus, so scientists have to stick to what they can collect. from a spacecraft in orbit.

VERITAS, one of two missions to Venus approved by NASA this year (the other, DAVINCI +, will study the planet’s atmosphere), will use state-of-the-art radar to create a High Definition 3D map of the surface of Venus and spectroscopy to analyze its composition. Its launch is scheduled for 2026.

Part of VERITAS ‘mission is to search for clues on the news of tectonic and volcanic activity on Venus. “We have a feeling it’s really young, but we don’t have any numbers for that yet,” Stock says. She says the models described by Byrne and her colleagues are “a great prospect of what we want to look for.”

The European Space Agency’s Venus Express, which analyzed the planet’s atmosphere from 2005 to 2014, found possible chemical clues of recent volcanic activity that scientists want to investigate further. EnVision, another European spacecraft launched in the early 2030s, will also collect high-resolution radar images and analyze the atmosphere of Venus, looking for signals of active volcanism.

If they’re lucky, VERITAS and EnVision might see evidence that blocks of crust have shifted in the years since Magellan orbit the planet. Given the slow march of geologic time, a few decades might not be enough to see a difference, so “It’s a hit in the dark,” Montesi says, but “you miss 100 percent of the hits you don’t take. “so they must at least try.

“It’s a really weird world out there,” Byrne says. “We have a lot more to explore and it’s going to be an exciting decade because we are going to get our questions answered.”


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