Tesserae are the most geologically complex regions seen on Venus. Stratigraphic studies of tessera terrain establish that they consistently appear locally, and perhaps even globally, as the oldest material on a planet with an average surface crater retention age of 750 million years.
A new study that sheds light on the enigmatic planet’s geological history has found that some of the oldest terrains on Venus, known as tesserae, have layering that seems consistent with volcanic activity. The study has shown that a significant portion of the tesserae has striations consistent with layering.
Paul Byrne, associate professor of planetary science at North Carolina State University and lead author of the study, said, “There are generally two explanations for tesserae—either they are made of volcanic rocks, or they are counterparts of Earth’s continental crust. But the layering we find on some of the tessera isn’t consistent with the continental crust explanation.”
For the study, scientists analyzed the images of Venus’ surface. The images were obtained from NASA’s 1989 Magellan mission, which used radar to image 98% of the planet through its dense atmosphere.
Before this study, the layering of the tesserae hasn’t been recognized as widespread. Byrne thinks that that layering would not be possible if the tesserae were portions of continental crust.
Byrne says, “Continental crust is composed mainly of granite, an igneous rock formed when tectonic plates move, and water is subducted from the surface. But granite doesn’t form layers. If there’s a continental crust on Venus, then it’s below the layered rocks we see.”
“Aside from volcanic activity, the other way to make layered rock is through sedimentary deposits, like sandstone or limestone. There isn’t a single place today on Venus where these kinds of rocks could form. Venus’s surface is as hot as a self-cleaning oven, and the pressure is equivalent to being 900 meters (about 985 yards) underwater. So the evidence right now points to some portions of the tesserae being made up of layered volcanic rock, similar to that found on Earth.”
“The work will help to shed light on more of Venus’ complicated geological history.”
“While the data we have now point to volcanic origins for the tesserae, if we were one day able to sample them and find that they are sedimentary rocks, then they would have had to have formed when the climate was very different—perhaps even Earth-like.”
“Venus today is hellish, but we don’t know if it was always like this. Was it once like Earth but suffered catastrophic volcanic eruptions that ruined the planet? Right now, we cannot say for certain, but the fact of the layering in the tesserae narrows down the potential origins of this rock.”
The research team included scientists from the U.S., the U.K, Turkey, Canada, and Russia. Images came from NASA’s Planetary Data System and Astrophysics Data System.
- Paul K. Byrne et al., Venus tesserae feature layered, folded, and eroded rocks, Geology (2020). DOI: 10.1130/G47940.1