Io, one of Jupiter's many moons and larger than our own. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and its moons Europa, Ganymede and Callisto. Several volcanoes produce plumes that climb as high as 300 miles above the surface. Io has more than 100 mountains, some of which are taller than Mount Everest.
