Ganymede is a natural satellite like Moon, it orbits the giant planet Jupiter and discovered by Galileo Galilei in January 1610.
It is the largest satellite in our Solar System, the second largest satellite is Titan which orbits the second largest planet Saturn. The diameter of ganymede is 5268 Km and it is larger than the planet Mercury, because of its largest size if ganymede orbits Sun it would be considered as a planet.