Ganymede is the largest natural satellite of any planet in the Solar System.
Ganymede orbits Jupiter and has a diameter of about 5,268 kilometres, making it larger than Mercury by diameter, although it has less mass. It is the only moon known to possess its own intrinsic magnetic field, which creates a small magnetosphere within Jupiter’s much larger magnetic environment.
The moon was discovered by Galileo Galilei in January 1610, along with Jupiter’s other three large Galilean moons: Io, Europa, and Callisto. Its name comes from Ganymede, a figure in Greek mythology who was taken to Olympus to serve the gods.
Ganymede has an icy outer shell and a differentiated interior, including a metallic iron core. Evidence indicates a saltwater ocean may exist beneath its ice. NASA’s Juno spacecraft has studied the moon during close flybys, while the European Space Agency’s JUICE mission is designed to investigate Ganymede and the Jovian system in greater detail.