No other solid body in the Solar System has a crust quite like Earth. From Mercury to Mars, as well as many moons, most worlds have a crust in a single piece. Our planet instead has tectonics, vast plates moving about on the molten upper mantle. Another exception to the single-block surface might be Venus, new evidence suggests.
Just looking at their size, you could think that Earth and Venus are twins. But even a quick glance at both planets shows that they are dramatically different. Venus is covered in an extremely dense acidic atmosphere with a temperature high enough to melt lead. Its surface is only known to us thanks to radar observation due to the thick clouds that cover the whole planet.
The analysis, published in the Proceedings of the National Academy of Sciences, suggests that Venus might have a lithosphere – what the rocky outer part of a planet is called – that is broken into chunks. These are not like Earth’s tectonic plates that can go over and under one another. The team describes them as similar to packed ice, so they can jostle about without creating the geological phenomena we see on Earth.
The chunks are much smaller than tectonic plates, and they also don’t travel as far. An exciting finding is that some of the chunks appear to have moved through some important lava fields on Venus. Planetary scientists are unsure how old these regions are, but as they are on top of everything else, they ought to be younger than the rest – and if the lithosphere chunks’ motion has left a mark, maybe the planet is more active than we thought.
“Some of the structures we have seen from this movement cut through some of the youngest surfaces of Venus,” lead author Professor Paul Byrne told IFLScience. “It is not definite evidence but it’s pretty strong circumstantial evidence that something is deforming the crust actively.”
The team discusses how the mantle could be driving this phenomenon, and while the resulting effect is not quite like plate tectonics, understanding what’s going on might give us some clues on how plate tectonics might have started on Earth sometime over three billion years ago.
Why hasn’t Venus got plate tectonics? One possibility is that places like Mercury have a very thick lithosphere, too thick for it to be broken apart even with a convective mantle. Venus instead has a thin lithosphere, so it’s broken apart but the chunks don’t sink. Earth is in the sweet spot where the thick chunks are broken and can sink under one another, creating mountain ranges for example.
The early Earth might have been like Venus, with a thinner crust and plate tectonics only starting when they became thick enough. These possibilities can be tested going forward, but will require a lot more knowledge of what’s going on on Venus.
The team used radar data from NASA’s Magellan, collected decades ago, that suggests geological motions consistent with a fragmented lithosphere. In particular, the motion doesn’t resemble what is seen on Earth at the edge of tectonic plates, but suggests that these crustal chunks just shimmied about over time. The team report at least 58 examples of these geological signatures in the paper and they are located all over the planet.
While the scientists expect more will be discovered from the data currently available, the game-changer will be the missions going to Venus towards the end of this decade. The missions will provide a much higher resolution map of the surface as well as a better understanding of the planet’s geology as a whole. And maybe they could even see changes in surface features since Magellan was around Venus if these changes happen fast enough.
“One of the big questions we have for Venus is how come we have a world, basically the same size as Earth but it’s anything but Earth-like,” Professor Byrne told IFLScience. “Anything we can learn about Venus is ultimately going to tell us about our own planet. Its past, its potential future, and what we might expect from Venus-sized planets orbiting other stars.”