gabbo529 writes "NASA scientists have discovered new information on one of Jupiter's moons, indicating it has a molten magma sub-surface (abstract). This discovery, made using data analysis from NASA's Galileo spacecraft, reveals why that particular moon is the most volcanic object known in the solar system. The moon, which is named Io, produces about 100 times more lava each year than all the volcanoes on Earth combined. The global magma ocean about 30 to 50 kilometers (20 to 30 miles) beneath Io's surface explains the moon's activity." Science has a nice graphic, too.