A moon bigger than Mercury. Ganymede is the biggest moon in the solar system, wider than the planet Mercury, and the only moon with a magnetic field of its own. ESA’s JUICE is on its way, to circle it from 2034.
A mosaic of Galileo and Voyager pictures, in black and white. Where no spacecraft looked, it is plain grey.
USGS Astrogeology, Galileo and Voyager global mosaic, public domain.