Jupiter was the fifth planet from the Sun and the largest planet within the Solar System. Jupiter was classified as a gas giant along with Saturn, Uranus and Neptune. Together, these four planets were sometimes referred to as the Jovian planets.
Surrounding the planet was a faint planetary ring system and a powerful magnetosphere. There were also at least 63 moons, including the four large moons called the Galilean moons that were first discovered by Galileo Galilei in 1610. Ganymede, the largest of these moons, had a diameter greater than that of the planet Mercury.