Despite their close similarities in mass and composition, Earth and Venus have evolved differently—at least for the past 0.5–1 billion years. For one thing, a runaway greenhouse effect on Venus has produced a mean temperature of 460 °C, hot enough to melt lead (see Physics Today, March 2017, page 19). For another, unlike the mobile tectonic plates on Earth, the outer layer of Venus—its lithosphere—has been thought to be both globally static and continuous.
Researchers led by Paul Byrne of North Carolina State University now argue that Venus’s lithosphere may be more Earthlike than earlier planetary scientists realized. Byrne and his team used radar images from NASA’s 1989–94 Magellan mission, which had mapped the surface of the planet in rich detail. In the new work, they found widespread evidence for Venus’s lithospheric thinning and thickening—the pushing and pulling apart of crust—in “belts,” tectonic structures much longer than they are wide, that pervade the planet’s many lowlands. They realized that the belt-bounded lowlands form a network of discrete crustal blocks—the largest the size of Alaska—that appear to have moved relative to one another in a manner akin to a jostling ice pack. Indeed, the crustal blocks were highly strained by the motion, which may still be ongoing. They are bordered by sets of “wrinkle ridges” that mark the blocks’ edges, as shown in the figure. (No prior study had recognized those intersecting belts as mechanically discrete blocks.)
The team developed a computer model of the deformation and found that convection in Venus’s mantle might be the driving force. What’s more, the convection may have been facilitated by a lower crustal layer that was weakened by the planet’s currently high surface temperature. The motion is not plate tectonics per se—no mountain ranges or giant, Earthlike subduction zones seem to exist on Venus—but Byrne and colleagues’ new results point to a coupling between the planet’s mantle and surface. Nowhere else in the solar system can such coupling be found except in continental interiors on Earth. (P. K. Byrne et al., Proc. Natl. Acad. Sci. USA 118, e2025919118, 2021.)
