As we've explored the Solar System, some items we're familiar with from Earth's geology have kept appearing in new places. Glaciers, volcanoes, and geysers have all been found on other planets and moons. With all that's familiar, it's easy to forget that one of the defining features of Earth's geology—plate tectonics—is notably absent. There are some hints of it on the icy crust of Europa, but it would have to be powered by a different mechanism there.
If there was an obvious candidate for hosting plates, it would be Venus, similar in size and composition to the Earth and home to active volcanoes. But most of Venus' surface appears to have been there for hundreds of millions of years with no sign of the tectonic recycling we have on Earth. New research, however, suggests that some of Venus' crust does get recycled, just through a radically different process—one that may have been active early in Earth's history.
While we've been able to map Venus' surface, the planet's thick atmosphere has limited what we know about its surface, and we've not had the sort of repeated imaging that can reveal active geology. Even though we know its surface is littered with volcanoes, for example, we're not currently certain whether any of them are active. But crater counts suggest that most of the material on the surface is hundreds of millions of years old and had been put in place by massive eruptions.
All of that would suggest an absence of plate tectonics, which regularly recycles large portions of the Earth's surface. But there are also some features like trenches and rifts that suggest something tectonic might be going on.
For many planetary scientists, the solution in these cases is to build computer models and see whether they can reproduce any of the features we see on Venus. But, according to the scientists behind the new research, computational models just aren't currently up to the task of doing a full, three-dimensional simulation of something as complicated as the mantle and crust of Venus. So, they went a bit old fashioned and created a physical model.
The model is basically a heating plate, some water, and finely ground sand. You can create a suspension of silica nanoparticles in water and, by altering the concentration, alter physical properties like the viscosity to match that of semi-molten rock. Put that solution on a heating plate, and it will start convecting, as hot areas become less dense and rise to the surface. That's analogous to the circulation of the rock in the mantle, driven by heat from Venus' core.
Leave the top of this system open, and a crust will form naturally as water evaporates off. The authors could watch the evolution of the system using cameras and even gently pull off the crust to analyze what happens.