Scientists at North Carolina State University (NCSU) in the US have reported that they have found evidence of tectonic motion in the crust – also called the lithosphere – of the planet Venus. Tectonics refers to the large-scale movement of rocks, originally in the Earth’s crust or lithosphere. On the giant scale, the Earth experiences plate tectonics, which is the motion of the 15 to 20 tectonic ‘plates’ into which Earth’s lithosphere is divided. The lithosphere of Venus is not divided into such giant plates.

“We’ve identified a previously unrecognised pattern of tectonic deformation on Venus, one that is driven by interior motion just like on Earth,” reported study lead and co-corresponding author and NCSU associate professor of planetary science Paul Byrne. “Although different from the tectonics we currently see on Earth, it is still evidence of interior motion being expressed at the planet’s surface.”

Previously, it had been generally assumed that Venus now had a solid, umoving, lithosphere. However, the NCSU team carefully examined radar images of the surface of the planet, collected by the Magellan spacecraft (launched by the US National Aeronautics and Space Agency in 1989 and which arrived at Venus in August 1990 and functioned for just over four years). They discovered evidence of tectonic motion on Venusian lowlands.

Tectonic motion on Venus takes the form of great blocks of rock ‘jostling’ against each other in the manner of broken pack ice chunks. The study of the radar images showed places where these blocks had pushed together, pulled part, rotated and slid past each other. The researchers then created a computer model of the deformation they had observed, and this showed that such deformation could have been caused by “sluggish” movement in the Venusian mantle (the layer which underlies the lithosphere on both Earth and Venus).

“These observations tell us that interior motion is driving surface deformation on Venus, in a similar way to what happens on Earth,” he pointed out. “Plate tectonics on Earth are driven by convection in the mantle. The mantle is hot or cold in different places, it moves, and some of that motion transfers to Earth’s surface in the form of plate movement. A variation on the theme seems to be playing out on Venus as well. It’s not plate tectonics like on Earth – there aren’t huge mountain ranges being created here, or giant subduction systems – but it is evidence of deformation due to interior mantle flow, which hasn’t been demonstrated on a global scale before.”

This discovery could show that Venus is still geologically active. A number of the observed ‘blocks’ have formed in and deformed young lava plains on the planet, meaning that their formation and motion happened relatively recently, in terms of geological time. It might even still be happening.