Venus and Earth were born at the same time and are almost identical in size, and yet these two worlds have become vastly different environments over the past 4.5 billion years. Earth, bursting with life, is constantly reinventing its geography through tectonic activity, while Venus is an almost laughably inhospitable world with what appears to be an inactive outer shell, at least according to many past studies.
But our nightmarish sister planet has proved to be full of surprises, and a new discovery shows a never-before-seen type of tectonic motion on Venus. The discovery was newly found in observations originally captured nearly 30 years ago. This detection has major implications for understanding Venus, and could also shed light on distant exoplanets as well as on Earth’s deep past.
Scientists led by Paul Byrne, associate professor of planetary science at North Carolina State University, identified blocks of planetary crust in the Venusian lowlands that appear to have moved around in the recent past, indicating ongoing tectonic motion. The team studied the formations, the largest of which is the size of Alaska, by scouring radar maps of Venus’ surface from NASA’s Magellan mission, an orbiter that studied the planet in the early 1990s until it deliberately plunged into its atmosphere, never to be heard from again.
The block structures hint at interactions between the surface and interior of the planet that “are not seen elsewhere in the inner Solar System except for continental interiors on Earth,” according to the team’s study, which was published on Monday in Proceedings of the National Academy of Sciences.
Venus’ mantle, a layer below the outer crust, appears to be pushing the blocks laterally—or, side to side—in a manner similar to the motion of pack ice structures on Earth. While previous studies have proposed that tectonic strain and potential lateral movements are occurring on Venus, Byrne’s team is the first to identify the detailed motions outlining these blocks, showing what looks like recent activity.
“For decades, there's been circumstantial evidence that Venus is volcanically active and I would bet a lot of money that it is erupting right now,” Byrne said in a call. “There’s nowhere else in the solar system as tectonically deformed as Venus, except perhaps parts of Earth. So, of course, the world is active, but we've never had definitive evidence from any mission that could prove it or show it. A lot of it is based on inference.”
In other words, the tantalizing discovery of these lateral motions is a rare piece of tangible evidence that Venus is geologically active, or that it is, at the very least, on a transitional continuum from an active to inert state. Though its tectonic motion is nowhere near as expansive as Earth, these movements still make Venus an outlier compared to most other worlds in the solar system, such as Mars, Mercury, and the Moon.
A 1,100-km-wide, false-color radar view of Lavinia Planitia, one of the lowland regions on Venus where the lithosphere has fragmented into blocks (purple) delineated by belts of tectonic structures (yellow).
Byrne is optimistic that observations captured by Magellan and other past Venus missions contain much more information about these complex processes. But enhanced imagery of the planet’s surface will also be necessary to understand exactly how all the weird features on Venus fit together into one model.
Fortunately, NASA just approved two new missions to Venus, and the European Space Agency greenlit one of their own. The trio of spacecraft, which are scheduled to arrive at Venus sometime in the 2030s, will be able to examine the nature of these crustal blocks and their implications for Venus’ modern activity.
As a fascinating yet mysterious world, Venus deserves to be the center of attention in these studies and missions. Even so, it also provides a useful analog for understanding all kinds of other environments, ranging from Earth at a time before the onset of modern plate tectonics to worlds located in distant star systems.
“One of our core questions for Venus is: why is Venus not like Earth?” Byrne said. “Is it just because it started out a little closer [to the Sun] and it was never able to escape the runaway greenhouse effect? Or was it some catastrophe that happened way later in its life? Those are the two models we have.”
The newly greenlit Venus missions will help to resolve that question, which would have big implications for understanding the search for life elsewhere in the universe. If Venus-like planets are likely to become as hellish at the surface as our neighboring world, it could reduce the odds of finding alien life on exoplanets at similar orbital distances. Venus is also instructive in this era of human-driven climate change, as it reveals the extreme consequences of a runaway greenhouse gas effect.
At the same time, tectonic motions on modern Venus may be somewhat analogous to the motions of Earth billions of years ago, during the time when the seeds of life were first planted on our planet. In this way, Venus is not only a land of mystery that has defied easy explanations for decades, it is also a crucial window into the emergence of life on Earth and, potentially, beyond our planet.
“We don't have a good working model for what we would call the geodynamics— the motion, the power, and the processes—shaping Venus today,” Byrne said. “We need one, and our paper helps add to this discussion and hopefully, adds the momentum of people actually studying it.”
“We don't understand Venus at all,” he concluded. “Not really.”