Jupiter, the fifth planet from the sun, is also the largest (Jupiter is twice as massive as all the other planets combined). Jupiter orbits 778,330,000 kilometers from the sun (5.2 AU), and has a diameter of 142,984 kilometers (that's big!). Jupiter has a mass of 1.900e27. Jupiter is the fourth brightest object in the sky (after the Sun, Moon, and Venus, respectivley). Jupiter rotates on it's axis once every 10 earth days. It has an orbit of 11.9 Earth years.

Jupiter is a Gas Planet. Jupiter is about 90 percent hydrogen and 10 percent helium. Jupiter also has traces of water, methane, ammonia, and 'rock.' Of the other gas planets, Saturn has a similar composition, but Uranus and Neptune have less hydrogen and helium.

Jupiter was named after the Roman King of the Gods (in Greek, Zeus). Jupiter was named after the King of the Gods because, not only is Jupiter the biggest planet, but it was the last planet known at the time it was named.

Jupiter has a core of rock, but most of the planet is made up of liquid hydrogen. This liquid metallic hydrogen is the source of Jupiter's strong magnetic field. The outer layer consists of hydrogen and helium that are liquid, but become gas further out.

Jupiter's atmosphere has distinct winds which create the different bands visible in pictures. Lightly colored bands are known as zones, while the darker bands are called belts. The Great Red Spot was first identified over 300 years ago. It is an area of high pressure with cloud-tops that are taller and colder than it's surroundings. Other smaller spots exist on Jupiter and on Saturn; it is not know how they form or how they survive for so long.

Jupiter has many, many interesting moons. These moons were the first objects observed that did not travel directly around the sun, which helped support Copernicus' theory. Amoung Jupiter's 63 known moons are the four most notable Galiean moons, Io, Europa, Ganymede and Callisto. Io is slightly larger than the Moon, and has active volcanos. Europa has an ice covering and very few craters.

Six spacecrafts have visited Jupiter. Both Pioneers, both Voyagers, Ulysses, and Galileo. Galileo has orbited the planet for 8 years, taking probes and collecting data. Even so, much about the interior of the planet and cloud makeup is still unknown.

Jupiter also has very faint rings. It's rings are darker in color than Saturn's, and made up of rock rather than ice. They were discovered by Voyager by mistake.