Jupiter, fifth planet from the Sun, may itself have been a prototype Sun which just wasn't big enough to become a star. As a planet, however, Jupiter is by far the largest of nine planets circling the Sun.

Jupiter alone is more than two-thirds of the total mass of all planets in our Solar System. It's about 318 times the mass of Earth. Although a thousand times smaller than the Sun, Jupiter is a big planet -- as big as 1,317 Earths.

Still, Jupiter wasn't big enough. If the planet had been several times more massive, it might have become a star as the pressure and temperature at its core triggered nuclear fusion. Jupiter is a big gas bag, with a relatively low density.

Way out there. Jupiter is more than five times farther from the Sun than the Earth, at a distance of 483.6 million miles. It orbits the Sun every 11.9 years.

Jupiter spins rapidly -- once every 9 hours 55.5 minutes. That causes it to be slightly flat. Its diameter at the equator is 88,700 miles, but the distance from its north pole to south pole is only 83,000 miles.

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Solar System:	The Sun
Inner System:	Mercury	Venus	Earth	Mars
Outer System:	Jupiter	Saturn	Uranus	Neptune	Pluto
Other Bodies:	Moons	Rings	Asteroids	Comets

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