Jupiter is the largest planet in the solar system. It is the fifth planet from the sun. Jupiter is a gas giant because it is so large and made of gas. The other gas giants are Saturn, Uranus, and Neptune. Jupiter's mass is 1.898, 6 times 10 to the 27th power kilogram, 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, Yuppiter. Jupiter is the third brightest object in the night sky, only their smooth and Venus are brighter. Jupiter has 79 moons. About 50 of them are very small less than 5 kilometers wide. The four largest moons of Jupiter, RIO, Europa, Ganymede, and Callisto, they are called the Galilean moons because Galileo Galilei discovered them.