The Jovian moon Io is famous for being the only other place that Earth in the Solar System to have active volcanism. But another feature has been intriguing scientists for a long time: How do its lonely mountains form?
The mountains are not associated with volcanos, but they are associated with crust and mantle interactions. As the magma flows out from the core, it puts the surface under pressure, building stress into the crust. This is released as a portion of the crust shoots up, forming the mysterious mountains.
This solution was obtained by two American researchers, Michael Bland and William McKinnon from Washington University, with the help of a computer simulation. The numerical experiment showed that as the interior of Io is squeezed, the strain localizes in a single fracture that propagates upwards, breaking the surface and forming the mountains.
"The compressive forces deep in the crust are incredibly high," McKinnon said in a statement. "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."
This result, published in Nature Geoscience, clearly explains why the mountains tend to be associated with patera – shallow depressions scattered across the surface of Io.
The numerical simulation shows that as the fracture propagates upwards, it creates a mountain as well as magma lakes called patera. Bland & Mckinnon
Volcanos and mountains are anti-correlated on Io. Volcanos carry heat and pressure away from the crust, but when volcanism slows down, thermal stresses increase, which lead to more mountains taking shape.
The mountains have an average height of 6 kilometers (3.7 miles), with the tallest one reaching 17.5 kilometers (10.9 miles) – huge in comparison to the modest size of the satellite.
"It's a novel mountain-forming mechanism that we don't see elsewhere in the Solar System," added McKinnon.
On Earth, mountains form when continental plates interact, raising one on top of the other. But McKinnon doesn’t exclude that this other mechanism was in play when our planet was young. He actually suggests that if the primordial Earth was covered by a shallow ocean, this is how the first land might have emerged.
Maybe by studying Io, we can learn something about how our planet looked billions of years ago.