The largest and most massive satellite is Ganymede, which is 2.017 times as heavy as the Earth’s Moon and has a diameter of 5,267 km (3,273 miles).

The diameter of Ganymede – discovered by Galileo Galilei in 1610 – is greater than the width of the USA. It is the largest moon of Jupiter and the largest moon in the Solar System. It is made of ice and rock and is believed to contain an ocean of salty water around 200 km below its surface. Its appearance is characterised by ancient cratered terrain and younger areas marked with grooves and ridges, formed by tectonic activity.