Io's global "ocean" of molten rock beneath the surface feeds its prolific volcanism, a new study finds.

Unlike Earth's magma, which tends to cluster in pockets around the edges of tectonic plates, Io's magma is found in a global reservoir at least 30 miles (48 kilometers) deep, the study suggests. This huge reserve of subsurface molten rock helps explain why Io is the most volcanically active object in the solar system, spewing out 100 times more lava than all of Earth's volcanoes combined.

NASA's Galileo reveals magma 'ocean' beneath surface of Jupiter's moon - Kids Science Zone
Internal Fire Bakes Jupiter's Pizza Moon Io - Mike Wall, Space.com