Jupiter and Earth,Computer artwork showing the relative sizes of Jupiter,the largest planet in the Solar System,and Earth. Jupiter is a massive gas giant planet,composed mainly of the gases hydrogen and helium. Traces of other gases are responsible for its distinctive colouration. Jupiter is 143,760 kilometres in diameter,but has the fastest rotation of all the planets,spinning on its axis every 9 hours and 50 minutes. Earth (lower left) is a small rocky planet,and has a diameter of 12,760 kilometres. Earth's moon is seen above it. It is one of the largest satellites in the Solar System,being 3476 kilometres across |