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Venus may experience volcanic activity, but it's different than on Earth. On Earth, mantle convection drives volcanism. But on Venus, thick regions of its crust could be convective. Image Credit: NASA
Even though Jupiter's moon Io is considered the most volcanically active world in the Solar System, Venus actually has more volcanoes and volcanic features on its surface. For a long time, scientists thought that most of these features and volcanoes were ancient remnants of the planet's geological past. However, newer research shows that Venus could still be volcanically active.
Io retains the crown for most active volcanoes in the Solar System, with more than 400. But with about 85,000 volcanoes, Venus is the overall king of volcanism. While Venus has largely been considered volcanically dormant, that's changing. Venus is difficult to observe and that's made its volcanism seem extinguished.
New research in the journal Physics of the Earth and Planetary Interiors shows that Venus' crust could still be convectively active. The paper is titled "On the possibility of convection in the Venusian crust," and the authors are Slava Solomatov and Chhavi Jain. Solomatov is a professor of Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, and Jain is a postdoctoral fellow at WashU.
Earth and Venus are sometimes referred to as 'sister planets' because they're both rocky, inner Solar System planets about the same size. Aside from those similarities, the planets are not much like siblings. Earth is temperate and life abounds in its oceans and on its land. Venus, as is well known to most people, is blisteringly hot and has a toxic atmosphere with extremely high pressure.
Still, the planets were likely much more similar at the time of formation, and how the two diverged is an active and intriguing area of study. For one thing, Venus is not able to shed heat the way Earth does.
Earth's plate tectonics help the planet shed excess heat and avoid the runaway greenhouse effect. This process is driven by convection in the planet's mantle, which also drives volcanic activity both at mid-ocean ridges and surface volcanoes.
This simple graphic shows the basics of mantle convection. It shows a mid-ocean ridge (spreading) and a subduction zone (subduction of the oceanic plate) as well as a volcano. (Illustration: eskp.de, Licence: CC BY 4.0)
Venus may experience a type of convection separate from Earth's mantle convection. The planet's convection may take place in the much thinner crust.
"Nobody had really considered the possibility of convection in the crust of Venus before," said Solomatov in a press release. "Our calculations suggest that convection is possible and perhaps likely. If true, it gives us new insight into the evolution of the planet."
Earth's mantle convection is like a conveyor belt of matter and heat. As the surface crust is subducted back into the mantle, it carries water with it that helps cool the mantle. It also takes CO2 from the atmosphere and solidifies it into rock. As material from the mantle rises due to convection, it creates mid-ocean ridges and volcanoes.
Both Venus and Earth have cores, mantles, and crusts, but their crusts are different in thickness. Earth's crust is about 40km thick in the continents and 6 km thick in the ocean basins. According to the authors, these are too thin to support convection.
Venus and Earth are similar in structure yet different in many other ways. Image Credit: Kane and Byrne, 2024
Venus's crust is likely thicker and stronger than Earth's. Depending on location, type of rock, and temperature, Venus' crust could be between 30 and 90 km thick. That may be thick enough, at least in some locations, to maintain convection. This would be crustal convection vs. Earth's mantle convection.
Solomatov and Jain developed new theories based on fluid dynamics and applied them to Venus.
"We evaluate the possibility of convection in the Venusian crust by utilizing recently developed scaling laws for the onset of convection in temperature and stress-dependent viscosity fluids, heated from below or from within," the authors write. They determined that within "plausible ranges of surface heat flux, crustal thickness, and rheologies," crustal convection is possible. Rheology is basically the study of how materials flow and how they're influenced by viscosity and other forces. The implication is that the physical properties of the Venusian crust don't prohibit convection.
"Crustal convection, if it occurs, would affect the heat transfer across the Venusian crust and may produce various surface features such as novas and coronas," the authors write in their paper.
The problem is finding evidence of crustal convection on Venus's surface. Venus's thick clouds make it impossible to see the surface in optical light, making radar necessary to examine it. Fortunately, NASA's Magellan spacecraft successfully mapped almost the entire surface of Venus with radar, and the Pioneer Venus Orbiter also carried a surface radar mapper.
Surface images show that some features on Venus have melted, which is evidence of crustal convection. Lava flows from some shield volcanoes and volcanic plains show evidence of recent melting, and some appear to be geologically young. Scientists have puzzled over this because the planet's mantle isn't convective. The researchers' new results show that mantle convection may not be necessary.
"Our study shows that convection in the Venusian crust is clearly possible, although it most likely occurs at supersolidus temperatures, that is when the base of the crust undergoes melting," the authors write.
"Supersolidus" is when rocks and minerals are partially melted between the solidus, which is the temperature at which melting begins, and the liquidus, which is the temperature at which a material is completely melted. This is an important part of understanding Earth and other differentiated planets. It means materials can separate by density, with denser materials sinking and lighter materials rising. In supersolidus, the physical behaviour of materials changes significantly, affecting tectonic processes and mantle convection.
If rock can become supersolidus in Venus' crust, that could explain the planet's crustal convection.
Crustal convection can't take place all over Venus, according to the researchers. "The regions where the crust is predicted to be the thickest are most likely to undergo convection, although these predictions vary depending on the assumptions and the approach used," they write. Some regions with thick enough crust include Themis, Bell, Ovda, and Phoebe Regios. The crust could be up to 80 km thick in these areas.
These results may apply to other planets as well. "While our study is focused on Venus, our approach can be applied to other planetary bodies within the Solar System and to exoplanets. Planetary bodies with thick crust and hot interiors would be particularly interesting to investigate," the researchers write in their paper.
Remarkably, frigid, distant Pluto may experience crustal convection. The New Horizons mission found strange polygonal surface patterns in Pluto's Sputnik Planitia region. They resemble the boundaries between plates on Earth and can be explained by crustal convection in Pluto's ice.
The vast nitrogen ice plains of Pluto's informally named Sputnik Planum contain unusual polygon shapes that are similar to Earth's plate boundaries. Image Credit: NASA/JHUAPL/SwRI
"Pluto is probably only the second planetary body in the solar system, other than Earth, where convection that drives tectonics is clearly visible on the surface," Solomatov said. "It's a fascinating system that we still need to figure out."
Crustal convection is different from mantle convection in some important ways. It takes place on a smaller scale, meaning that higher-resolution instruments will be critical to detecting them. Fortunately, future planned missions to Venus should be able to detect crustal convection regions.
More:
Press Release: Could convection in the crust explain Venus’ many volcanoes?
Published Research: On the possibility of convection in the Venusian crust
Evan Gough
Evan Gough is a science-loving guy with no formal education who loves Earth, forests, hiking, and heavy music. He's guided by Carl Sagan's quote: "Understanding is a kind of ecstasy."