Jupiter was believed by Mesopotamians to be a wandering star placed in the heavens by a god to watch over the night sky.

The fifth planet from the sun is a huge ball of gas so massive it could hold all the other planets put together. What we can see of the planet are bands of the highest clouds in a thick atmosphere of hydrogen and helium. Traces of other gases produce the bright bands of color.

Jupiter's most familiar feature is swirling mass of clouds that are higher and cooler than surrounding ones. Called the Great Red Spot, it has been likened to a great hurricane and is caused by tremendous winds that develop above the rapidly spinning planet. Winds blow counterclockwise around this disturbance at about 250 miles per hour. Hurricanes on Earth rarely generate winds over 180 miles an hour. The Red Spot is twice the size of Earth and has been raging for at least 300 years. It is one of several storms on Jupiter.

At Jupiter's center is a core of rock many times the mass of Earth. But the bulk of the planet is a thick gaseous murk that appears smeared through a telescope because the planet moves so rapidly beneath. Jupiter's rapid rotation causes it to bulge, making the diameter 7 percent greater at the equator than at the poles.

Jupiter has thin, barely perceptible rings and at least 16 satellites. The four largest - Io, Europa, Ganymede and Callisto - are called the Galilean moons. They orbit in the same plane and are all visible in a telescope.