Ganymede is the largest moon of Jupiter and the entire solar system. It has a diameter of about 5,268 kilometers, making it even larger than the planet Mercury. Ganymede is unique because it has its own magnetic field, which is rare for a moon. The surface of Ganymede is a mix of two types of terrain: bright, icy regions and darker, older areas filled with impact craters. Scientists believe that beneath its icy crust, Ganymede may have a subsurface ocean, which raises the possibility of conditions suitable for life.