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.
The Red Spot
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
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.
JUPITER: RULER OF THE ROMAN GODS, ALSO JOVE
Jupiter was believed by Mesopotamians to be a wandering star placed in the
heavens by a god to watch over the night sky. In 1610, Galileo Galilei used a 20x
telescope to observe three "stars" around Jupiter. Over several nights he
observed these "stars," but each night they were in different positions, leading to
his conclusion that they were bodies orbiting the giant planet.
In 1994, astronomers around the world watched as the fragments of comet
Shoemaker-Levy 9 struck Jupiter - an event that had been forecast. This image
shows a bright cloud more than 8,600 miles in diameter caused by the impact.
You could stuff 1,300 Earths into Jupiter.