An Explanation for the Look of Venus’ Mysterious Surface

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• Robert Monroe- [email protected]

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A research team led by geophysicists at UC San Diego's Scripps Institution of Oceanography provides an explanation for features that characterize the surface of the solar system's hottest planet.

Venus' surface is pocked with round, crown-like features known as coronae. The more-or-less round features can look like terraced hills pushed upwards by heat energy or collapsed souffles, sunken as supporting materials beneath them cool off and contract.

In certain areas, the coronae are as much as ten times the size of others. In a study published today in the journal Proceedings of the National Academy of Sciences, the team presents evidence for the forces that form these landmasses.

"On Venus, there is a pattern that is telling us something," said lead author Madeleine Kerr, a PhD candidate at Scripps Oceanography. "We think what we found is the key to unlocking the mystery of the origin of these coronae."

This work, funded by NASA and the Department of Energy, helps scientists understand Earth's "twin" in the solar system. Venus is the closest neighbor planet to Earth, and roughly the same size. Because its atmosphere is densely packed with greenhouse gases, it is even hotter than Mercury despite being farther away from the Sun.

Venus is a closer analogue to Earth even than Mars, despite international interest in Mars leading countries to plan crewed missions to the Red Planet toward a possible goal of human habitation there.

Kerr said one value of studying Venus is in understanding what happened there to make it unable to support biological life while it flourishes on Earth.

"We get to have this solar system-sized laboratory," she said. "We have a front row seat to see why these planets are so different."

The researchers mapped the paths of bursts of magmatic energy pushing outward from Venus' core (nearly 3,000 kilometers or 1,900 miles deep) as on Earth. The planet has a single rigid crust over the entire surface of the planet, unlike Earth that has moving tectonic plates. Hot upwellings, like the blobs that rise in a lava lamp, can push through from the core and make large (2,000-kilometer or 1,200 mile-wide) volcanic structures.

But many of these hot channels of magma don't have that much energy. When they approach the surface about 600 kilometers (400 miles) deep, they are blocked by a layer in the mantle that forms due to the changing crystal structure of the rock, creating what researchers term a "glass-ceiling" effect. After some of the hot rock is blocked, even smaller blobs can rise up towards the surface from this shallower layer. These smaller blobs may form the abundant and smaller coronae features seen scattered across the planet's surface.

Scripps geophysicist David Stegman, Kerr's research advisor, likened scientists' understanding of why Venus' surface looks the way it does to the field's understanding of Earth's before plate tectonic theory provided a compelling explanation some 50 years ago.

"The current state of knowledge of the planet Venus is analogous to the 1960's pre-plate tectonic era because we currently lack an equivalent unifying theory capable of linking how heat transfer from the planet's interior gets manifested into the tectonics and magmatic features observed on Venus' surface," Stegman said. "With this new explanation for Venus' surface features, we feel a revolution has begun and even more exciting discoveries are just around the corner."

Besides Kerr and Stegman, study coauthors include Suzanne Smrekar of the NASA Jet Propulsion Laboratory (JPL), and Andrea Adams of Scripps and JPL.