Jupiter's Io satellite has a layer of molten rock under the surface and can reach a width of more than 50 kilometers, according to researchers from the University of Michigan and UCLA. They have reached this conclusion by analyzing how the magnetic field of Jupiter is diverted by crossing Io. In fact, they have seen that only one zone of high conductivity can deviate like this. In particular, they have explained that this mantle is formed by molten ultramaphic rocks.