To call Venus a truly strange planet of a planet would be to slightly understate the problem. It is so very similar to Earth – and yet at the same time as unlike Earth as you would expect an Earth-like planet to be.
One of these differences is the Venusian lithosphere – the planet’s hard, outer shell. On Earth, the lithosphere is fragmented and mobile, divided into tectonic plates that help shape the planet’s surface, while also leaking heat from the planet’s interior around its jagged edges.
Venus’ lithosphere, on the other hand, is seamless, making the mechanisms behind the planet’s cooling and reemergence something of a mystery.
A new study suggests that Venus may actually have a relatively “squishy” lithosphere that regularly resurfaces.
Studying these mechanisms is complicated and difficult: Venus is suffocated by a thick toxic atmosphere that rains acid and keeps its surface temperature at an average of 475 degrees Celsius (887 degrees Fahrenheit). Landers sent there have not lasted long.
But data collected by the Magellan orbiter decades ago may have kept Venus’ secrets all these years. The spacecraft used radar to penetrate the planet’s thick clouds and image its surface – and now scientists have used this data to discover that Venus’ lithosphere may be thinner than previously thought.
Led by planetary geophysicist Suzanne Smrekar of NASA’s Jet Propulsion Laboratory, a team of scientists used Magellan data to make a close study of volcanic surface features called coronae and the trenches and ridges that surround them. They found that where the mountain ridges are closer together, the lithosphere is likely to be quite thin and flexible, about 11 kilometers (7 miles) on average.
Modeling suggests that heat flow through the surface is higher in these locations than the average heat flow on Earth.
“For so long we’ve been locked into this idea that Venus’ lithosphere is stagnant and thick, but our view is now evolving,” explains Smrekar.
“While Venus does not have Earth-like tectonics, these areas of thin lithosphere appear to allow significant amounts of heat to escape, similar to areas where new tectonic plates are forming on Earth’s ocean floor.”
For a long time, scientists believed that Venus currently doesn’t have much going on inside, but recent studies have increasingly suggested otherwise. Coronae is one of those hints.
These features look a bit like impact craters, and consist of a raised ring (like a crown) around a sunken center, with concentric fractures radiating outward. They can also be huge, hundreds of kilometers across.
Scientists originally thought coronae our craters, but closer analysis showed that they are actually volcanic in nature. They are caused by plumes of hot molten material billowing up from the planet’s interior, pushing the surface upward into a dome that then collapses inward as the cloud cools, leaking from the sides to form a ring.
In truth, impact craters are relatively few and far between on Venus, at least compared to planets like Mars and Mercury. This contrast has long been something of a puzzle. The more impact craters a planet has, the older the surface is estimated to be. If a planet has few impact craters, something must have erased them.
Venus’ surface is 80 percent volcanic rock, which implies some kind of mechanism for putting the planet’s inside out in the planet’s recent past. A growing number of clues suggest that such volcanism is not just recent but ongoing, keeping the planet’s surface young.
The work of Smrekar and her colleagues supports this hypothesis. Ongoing heat loss in Venus’ coronal regions points to ongoing geological activity as magma rolls just below the surface.
Unfortunately, compared to Mars, Venus has been deprived of our attention in recent years, so there is a genuine lack of up-to-date data; The Japan Aerospace Exploration Agency’s Akatsuki probe is currently the only dedicated Venus mission. For a planet so similar to Earth, this seems like an oversight, despite the challenges, but a number of agencies have Venus missions in development.
For NASA, that’s the VERITAS mission, an orbital probe scheduled for launch in 2027. Scientists hope they’ll be able to use it to take a much closer look at Venus’ curious coronae.
“VERITAS will be an orbiting geologist, able to find out where these active areas are, and better resolve local variations in lithospheric thickness. We will even be able to capture the lithosphere in the process of deforming,” says Smrekar.
“We want to find out if volcanism really makes the lithosphere ‘squishy’ enough to lose as much heat as Earth, or if Venus has more mysteries in store.”
The research is published in Nature Geosciences.