Jupiter is the largest planet in the Solar System. It is the fifth planet from the Sun. Jupiter is a gas giant, both because it is so large and made up of gas. The other gas giants are Saturn, Uranus, and Neptune.
Jupiter's mass is 1.8986×1027 kg, or about 318 times the mass of Earth. This is more than twice the mass of all the other planets in the Solar System put together.
Jupiter can be seen even without using a telescope. The ancient Romans named the planet after their King of Gods, Jupiter (Latin: Iuppiter). Jupiter is the third brightest object in the night sky. Only the Earth's moon and Venus are brighter.
Jupiter has 79 moons. About 50 of them are very small—less than five kilometres wide. The four largest moons of Jupiter are Io, Europa, Ganymede, and Callisto. They are called the Galilean moons, because Galileo Galilei discovered them. Ganymede is the largest moon in the Solar System. Its diameter is larger than the planet Mercury's.