Beneath the cloudy, thick atmosphere of Venus, the planet's surface shows signs of activity that may be much more recent than ancient, according to a new study.
Scattered across the planet's hot surface, where temperatures of 880 degrees Fahrenheit are hot enough to melt lead, structures called coronae can be seen, based on maps provided by previous missions to Venus.
This area is known as Venus' own "Ring of Fire," and researchers suggest these locations could be targets for future missions to Venus.
These coronae take their name from the Latin word for crown, which is fitting given that they leave crown-shaped structures on the planet's surface.
They have formed where plumes of hot magma from deep inside the planet make their way up through the planet's mantle and crust -- not unlike how the volcanic Hawaiian Islands formed on Earth. These massive crowns on Venus are surrounded by cracks and lines that stretch out from the center.
Although coronae are signs of tectonic and volcanic activity on Venus, they're not exactly volcanoes like the ones we have on Earth.
Coronae are massive, some in the new study reaching larger than 186 miles in diameter, according to Anna Gülcher, study author and postdoctoral candidate at the Swiss Federal Institute of Technology's Institute of Geophysics in Zurich.
The study was published Monday in the journal Nature Geoscience.
Unlike the volcanoes we have on Earth, coronae are more like fields of lava flows and faults in a circular shape -- but each one is the result of a single plume of magma that comes near the surface from the planet's interior, Gülcher said.
And much like Mars, Venus doesn't have tectonic plates. Its tectonic activity is evident through faults, coronae, mountains and rift valleys.
While many of these coronae are evidence of ancient activity on Venus, a new study has identified 37 coronae that they consider to be recently active, which suggests that the planet is geologically active and its interior is still warm.
Other planets in our solar system, like Mars and Mercury, have cold interiors.
Previously, scientists believed that Venus had cooled to the point that its geologic activity had slowed. They believed its crust was so hard and tough that no material from the inside would be able to burst through it.
For their study, the researchers modeled activity in Venus' interior to simulate how coronae form.
The researchers discovered that features of coronae located all across Venus tend to vary, showing their development and evolution. And if coronae are still forming and evolving, that means that inside Venus, its warm interior is still "churning."
But how recent is this activity?
"It could be today or a couple million years ago," said Laurent G.J. Montesi, study coauthor and professor in the University of Maryland at College Park's geology department, in an email.
"What we know is that if a plume stopped being active more than 2 or 3 million years ago, some of the attributes of our 'active' coronae would have vanished," he said.
"In many of these structures, the attributes we associate with activity are very well marked, suggesting that activity is indeed recent or ongoing. Based on what we know of volcanoes on Earth, this could means eruptions every few hundreds of years."
The 37 active coronae are located in specific locations in a broad band across the southern hemisphere, which suggest these are areas of activity on Venus. There were only a small number of active coronae outside of this area.
Venus isn't the only planet with a so-called "Ring of Fire." Earth has its own "Ring of Fire" in the Pacific Ocean, where active volcanoes and frequent earthquakes contribute to the name. However, on Venus, this ring is being created by the mantle plumes responsible for coronae.
"The reason behind such distribution of active mantle plumes on Venus, and its link with the dynamics of the deeper within the planet, is key for future geodynamic studies," Gülcher said.
Earth's unusual twin
Venus is similar in size to Earth and often referred to as Earth's twin, but it's also considered to be an unusual planet that scientists are still trying to understand. Despite the fact that multiple missions have conducted flybys and imaging of Venus over the years, its inhospitable surface makes landing on the planet and studying it in detail more tricky.
For this study, data gathered during NASA's Magellan mission, which orbited Venus between 1990 and 1994 and mapped almost the entirety of the planet, was used to look at the planet's topography.
For instance, Venus has surface features that are considered "young," astronomically speaking, and differ in age when compared to the solar system's formation 4.5 billion years ago. Many scientists have described a global resurfacing event between 500 million and 700 million years. After that resurfacing event, likely caused by volcanic processes on the planet, it was considered "geologically dead."
This new study, and other recent research, suggests otherwise. These coronae are part of the growing evidence that Venus is experiencing a more gradual resurfacing and cooling process. This is similar to Earth's volcanic activity. The coronae could help Venus gradually lose its internal heat and create resurfacing on a much smaller scale, Gülcher said.
The fact that the researchers found active coronae, as well as what they refer to as much older "fossil corona structures," show that this process has taken place across Venus for a long time, the researchers said.
Much of the data the researchers have to work with has poor resolution, so future missions to Venus like the European Space Agency's EnVision launching in the 2030s and NASA's proposed VERITAS mission concept could provide more high-resolution data of the planet's geodynamics and topography.
And, of course, if it were possible, rock samples collected from the surface of Venus would provide more information about the planet's composition and interior.
Based on the current information they have, the researchers are interested in learning more about these hotspots in Venus' southern hemisphere and what it suggests about how and why Venus' interior is reacting that way in such a localized area.
"The atmosphere of Venus is likely fed by volcanic activity, and understanding that history will help us know how and why Venus became such a hellscape, maybe even teach us how to better manage the Earth's climate," Montesi said.
But a broader questions remains.
"A key general question that still remains to be answered is how and why Earth and Venus took such different evolutionary paths, when supposedly starting out with the same composition," Gülcher said..
"By better understanding the geophysical processes that causes the tectonic and magmatic features on Venus, scientists may also gauge their impact on the planet's climate, and, possible, answer another essential question: why does Earth is habitable, and Venus not?"