Ganymede

Facts 

Ganymede's Diameter is 5,262 km ( 3,270 mi ) which makes this satellite bigger than any other satellite in the solar system and is 7% larger than the planet Mercury. Ganymede even if it is larger than Mercury it is about half the mass of Mercury, which means it's density is less.

Ganymede is the satellite of Jupiter. It is one of the moons discovered by Galileo Galilei they were Callisto, Ganymede, Io and Europa. Ganymede was named after the lover of Zeus. 

Ganymede's orbital period is very fast it is just 8 days.

Ganymede was discovered on 7 January 1610 it was Discovered with 3 other moons that I mentioned earlier. The Galilean moons proved that the earth is not the only planet to have moons and earth was not the center of the solar system but the Sun was the center of the solar system.