Ever since Soviet spacecraft first captured images of the Venusian surface in the mid-1970s, certain features stood out. Photographs and subsequent radar images revealed a planet teeming with volcanoes, frozen lava plains, and vast, deformed highlands twisted and strained by strong planetary forces. 

Those highlands, called tesserae, have inspired intense debate and speculation. For decades, the prevailing thought has been that the tesserae represent the oldest regions of Venus’s surface, remnants of the ancient stressors that shaped the planet millions and billions of years ago.

Now, a team of international scientists led by Paul Byrne, an associate professor of Earth, environmental, and planetary sciences, has offered a bold new theory on the origins of at least some parts of these enigmatic tesserae. The theory, published in JGR Planets, holds that perhaps not all parts of these ancient highlands are so ancient after all. 

“Tesserae have been proposed to be analogous to the continental crust on Earth,” Byrne said. Specifically, they seemed to resemble the oldest outcrops of rocks on Earth, such as the Pilbara Craton of Northwest Australia, a region that has been geologically undisturbed for more than 3 billion years. The assumption that tesserae are old continents suggests that Venus may have once had Earth-like land masses surrounded by Earth-like oceans, a very different world than we see today.

The idea that Venus — our closest planetary neighbor and Earth’s near twin in terms of size — could have had continents built by classic tectonic forces had its appeal. But Byrne and colleagues from the United States, the United Kingdom, and Turkey used new modelling techniques and a fresh look at radar images to offer a more nuanced perspective: Instead of being wholly ancient parts of the crust, the tesserae of Venus may have a broad range of ages, some with margins that are relatively young and still evolving. 

“We believe that the margins of some of the tesserae we see today were formed by recent geological activity,” said Byrne, who is also a fellow of the McDonnell Center for the Space Sciences. If true, he added, the surface of Venus is both younger and more dynamic than previously assumed.

It’s impossible to precisely determine the age or composition of a planet’s features from radar images alone, but Byrne and co-authors have built an explanation of tesserae that fits with existing observations and the tenets of planetary science. 

To understand the highlands, Byrne said, it’s crucial to understand the surrounding plains. The general shape and patterns of the plains suggest they are mostly frozen lava flows, a product of the volcanism that continues to roil the planet. 

For several years, Byrne has been building a case that tesserae may be linked to these lava plains in a way not previously recognized. In 2021, he led an international study presenting evidence that at least some tesserae had distinct layers, implying that they were either formed by sedimentation or, more likely, multiple lava flows layered upon each other. Either way, these are not the processes that form Earth’s continental crusts, Byrne noted. 

In the latest paper, Byrne and co-authors build on the idea that tesserae are at least partly formed by deformed lava plains. They modeled the forces that should be present on the volcanically active planet and found that they are likely strong enough to turn previously flat plains into twisted, deformed highlands. “If you crunch this stuff up enough, geologically recent plains material could end up looking like tesserae,” Byrne said.

There’s no reason to assume that the features have finished evolving, Byrne said. “It’s highly possible that the activity is ongoing,” he said. “My gut feeling is that if we look at very high-resolution images of tesserae taken 40 years apart, we’d see subtle but significant changes.”

Byrne and colleagues intend to expand on their theories in future papers that will more thoroughly investigate the likely compositions and ages of tesserae. Future missions, such as NASA’s VERITAS, a project that will create the first global, high-resolution radar images of the planet’s surface, will certainly clarify the picture.

While Byrne’s new view of tesserae departs from the conventional idea that such terrain is uniformly ancient, he believes the insights paint a clearer picture of our planetary neighbor’s true identity: A world that continues to evolve and surprise.