Jupiter has at sixteen moons that we know of, possibly more.  Most of the moons are small and covered with ice.  Jupiter's largest moons are Ganymede, Callisto, Io, and Europa.  Ganymede is the largest of Jupiter's moons, larger than the planets Mercury and Pluto.  Io is the only moon in the solar system with live volcanoes.  These volcanoes erupt frequently, spewing out hot molten sulfur.  Europa and Callisto are covered by huge oceans of ice.