Jupiter is the biggest planet in the Solar System. However, a day on the planet only takes 9 hours and 55 minutes, meaning that the planet spins very fast, although a year on Jupiter (the length of time it takes for the planet to orbit the Sun) takes 11.9 years. This is because the planet is so far away from the Sun. The planet is made up mainly of hydrogen and helium, and, as far as we know, does not have a solid core (although may have a metallic liquid hydrogen core). Jupiter also has a magnetic field which would make the planet appear as big as the Sun if it was visible. Its main feature is a Great Red Spot, which is a storm that has been going on for years. The planet has 63 confirmed moons, with two moons larger than the planet Mercury and dwarf planet Pluto!