The active surface of Venus examined

Credit: NC State University, based on original NASA / JPL images

Despite their close similarities in terms of mass and composition, Earth and Venus have evolved differently, at least for the past 0.5 to 1 billion years. On the one hand, an uncontrollable greenhouse effect on Venus produced an average temperature of 460 ° C, high enough to melt the lead (see Physics today, March 2017, page 19). On the other hand, unlike the moving tectonic plates on Earth, the outer layer of Venus – its lithosphere – has been viewed as both globally static and continuous.

Researchers led by Paul Byrne from North Carolina State University now claim that Venus’s lithosphere may be more Earth-like than previous planetary scientists thought. Byrne and his team used radar images from NASA’s Magellan mission from 1989 to 1994, which mapped the surface of the planet with great precision. In the new work, they found widespread evidence for the thinning and thickening of the lithosphere of Venus – the pushing and spreading of the crust – in “belts,” tectonic structures much longer than they are wide. , which invade the many lowlands of the planet. They realized that the lowlands bounded by the belt form a network of discrete crustal boulders – the largest the size of Alaska – that appear to have moved relative to each other in a manner similar to an ice floe compass. Indeed, the crustal blocks have been heavily stressed by the movement, which may still be ongoing. They are bordered by sets of “ridges of ridges” which mark the edges of the blocks, as shown in the figure. (No previous study had recognized these crossing belts as mechanically discrete blocks.)

The team developed a computer model of the deformation and discovered that convection in the mantle of Venus could be the driving force. Additionally, 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 giant Earth-like mountain ranges or subduction zones appear to exist on Venus – but new findings from Byrne and his colleagues indicate coupling between mantle and mantle. surface of the planet. Nowhere else in the solar system can such a coupling be found except in the continental interiors of Earth. (PK Byrne et al., Proc. Natl. Acad. Sci. United States 118, e2025919118, 2021.)

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