Jupiter is the largest planet in the Solar System.[11] It is the fifth planet from the Sun.[12] 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 has a mass of 1.8986×1027 kg, or about 318 Earths.[2] This is twice the mass of all the other planets in the Solar System put together.[13]
Jupiter can be seen even without the use of telescope. It was known to the ancient Romans, who named it after their god Jupiter (Latin: Iuppiter).[14][15] Jupiter is the third brightest object in the night sky. Only the Earth's moon and Venus are brighter.[16][17]
Jupiter has at least 79 moons. Of these, around 50 are very small and 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. It is larger in diameter than even Mercury. In 2018 another 10 very small moons were discovered
Structure
Jupiter is the biggest planet in the Solar System with a diameter of 142,984 km. This is eleven times bigger than the diameter of Earth.[19]
An animation of part of Jupiter's cloud system. The animation is made of over 40 photographs taken by the Cassini spacecraft between October 31 and November 9, 2000.
Four photographs of Jupiter taken in 1994. The bright white spots are explosions where parts of the comet Shoemaker Levy-9 hit the planet.
A picture by an artist of the Voyager 1 spacecraft that flew past Jupiter in 1979.
Atmosphere
The atmosphere near the surface of Jupiter is made of about 88 to 92% hydrogen, 8 to 12% helium, and 1% other gases.[2]
The lower atmosphere is so heated and the pressure so high that helium changes to liquid. It rains down onto the planet.[20] Based on spectroscopy, Jupiter seems to be made of the same gases as Saturn. It is different from Neptune or Uranus. These two planets have much less hydrogen and helium gas.[21]
The very high temperatures and pressures in Jupiter's core mean scientists cannot tell what materials would be there. This cannot be found out, because it is not possible to create the same amount of pressure on Earth.
Above the unknown inner core is an outer core. The outer core of Jupiter is thick, liquid hydrogen.[22] The pressure is high enough to make the hydrogen solid, but then it melts because of the heat.
Mass
Jupiter is twice as massive as all the other planets in the Solar System put together.[13] It gives off more heat than it gets from the sun.[23] Jupiter is 11 times the width of Earth and 318 times as massive. The volume of Jupiter is 1,317 times the volume of Earth. In other words, 1,317 Earth-sized objects could fit inside it.