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How to Form Io's Mountains? Just Squeeze!

Jupiter's moon Io mysterious
Jupiter's moon Io is a hotbed of volcanic activity and much of its geology remains a mystery. (Image credit: NASA)

Jupiter's volcanic moon Io is full of mysteries, including how its mountains were formed. They have puzzled scientists for decades because they look nothing like mountains on Earth.

At home, we see mountains grow in ranges that can stretch across thousands of miles. But on Io, the more than 100 cataloged mountains mostly grow in isolation. What mysterious tectonic forces are at play here?

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Io is so active that it's hard to look at the tectonics from space; molten lava coats the surface at an incredible rate of five inches per decade. So to answer the question, a new study used simulations to figure things out.

A close-up of Mongibello Mons at sunset. The mountain is about 8.6 kilometers (5 miles) high. Io has mountains that are as high as 10 miles above the plain, which is taller than Earth mountains. (Image credit: NASA/JPL/University of Arizona)

"The planetary community has thought for a while that Io's mountains might be a function of the fact that it is continuously erupting lava over the entire sphere," lead author William McKinnon, a planetary scientist at Washington University in St. Louis, said in a statement. He co-wrote a paper about this in 2001.

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"All that lava spewed on the surfaces pushes downward and, as it descends, there's a space problem because Io is a sphere, so you end up with compressive forces that increase with depth."

The new work simulates this hypothesis, but focuses on the fact that Io's compression gets stronger as you go deeper into the moon. This creates strain in a single fracture created deep inside of Io and then erupting to the surface, creating a cliff. The scientists also suggest this could explain why so many recent eruptions are found near the mountains.

The south polar region of Io as seen by Voyager 1. This includes the mountain Haemus Mons, which is 10 kilometers (32,000 feet) high. It is visible at bottom. (Image credit: NASA/JPL/USGS)

"The compressive forces deep in the crust are incredibly high," McKinnon said. "When these faults breach the surface, those forces are released, and the entire stress environment around the fault changes, providing a pathway for magma to erupt."

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The simulations also may show why Io has some mountains that split over time. That's because the lava inside the crust creates both compression and high temperature. Heating rocks causes them to split because they have nowhere to expand to. This is especially prevalent when the volcano is not erupting and carrying away the lava, reducing the pressure.

The work was published in Nature Geoscience.

Originally published on Discovery News.

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Elizabeth Howell

Elizabeth Howell is a contributing writer for who is one of the few Canadian journalists to report regularly on space exploration. She is the author or co-author of several books on space exploration. Elizabeth holds a Ph.D. from the University of North Dakota in Space Studies, and an M.Sc. from the same department. She also holds a bachelor of journalism degree from Carleton University in Canada, where she began her space-writing career in 2004. Besides writing, Elizabeth teaches communications at the university and community college level, and for government training schools. To see her latest projects, follow Elizabeth on Twitter at @howellspace.