Ganymede is the largest moon in the solar system. It is one of the many moons orbiting the largest planet in the solar system, Jupiter. Ganymede has a diameter of about 5,268 kilometers, or 3,270 miles.
Ganymede was discovered by astronomer Galileo Galilei and was one among four moons that Galileo observed through his telescope. Ganymede's size even surpasses another planet in the solar system, Mercury. Ganymede is large enough that it could have been a planet had it orbited the sun instead of Jupiter.
A unique feature of Ganymede is that of all the other moons in the solar system, it is the only one possessing a magnetic field generated by its metallic iron core. Surrounding the iron core is a mantle made up of rocky material. Above the rocky mantle lies an icy shell that also forms the moon's surface. Ganymede also has a thin atmosphere consisting of oxygen.