Io, one of the Galilean moons of Jupiter, is the most volcanically active body in our solar system. Its surface is littered with volcanoes that produce 100 times more lava each year than those n Earth do. Many of the circular shaped plateaus in the image above are volcanoes, and the dark one just left of center is currently erupting! Io does not have tectonic plates like that crack or get forced upward and cause volcanoes like Earth does. Instead, Io's volcanoes are formed because Jupiter tugs and squeezes the moon as it orbits. It squeezes so hard that the surface essentially pops like a zit and spews out lava (gross!).
Until recently, astronomers were unsure exactly where the magma was coming from. The magma could have originated at the very center of the moon, just under the surface, or anywhere in between. Astronomers used magnetic field data from the Galileo mission (a satellite that orbited Jupiter from 1995-2003) to discover that the magma sits just under Io's surface. The only way that Io could have produced the strange magnetic field signature observed by Galileo is if it has liquid ultramafic rocks directly below the surface. Ultramafic rocks are special rocks that when in liquid form can conduct high amounts of electricity. Earth's mantle is thought to contain a lot of these types of rocks. This magma ocean on Io is probably over 2200 degrees F! I sure wouldn't want to live anywhere near one of those volcanoes!
Image Credit: Galileo/JPL/NASA
