Jupiter's swirling, ever-changing clouds of red, yellow and orange gases have long been one of the most intriguing mysteries of space. Only recently, through the findings of several American space probes, have astronomers begun to fully unravel the secrets of the planet's clouds.
Photo. Jupiter, the solar system's giant planet. Notice the Great Red Spot in the center of the lower half of the picture; this spot alone is the size of two Earths. Courtesy NASA/Space Telescope Science Institute.
By far the largest planet in the Solar System, Jupiter, named for the king of the Roman gods, is the size of an incredible 1300 Earths -- making it a healthy one and one-half times as big as all of the other planets combined.
The fifth planet from the sun, Jupiter orbits the sun at a comfortable distance of at least 480 million miles, completing one full revolution every twelve Earth years.
Every ten hours on Earth, Jupiter completes another turn around its axis, spinning more than twice as quickly as the earth and thus making its days less than half as long as ours. This rapid rotation whips up winds which whirl sometimes in excess of 250 miles per hour, constantly changing the configuration of the planet's colorful clouds.
Blown hundreds of miles each month, the clouds which make up Jupiter's atmosphere appear to us as swirling, ever-changing streaks of red, orange, yellow and tan. The top layer of the clouds is made up of hydrogen gas, with a temperature of a brisk -250 degrees Fahrenheit. The lower clouds in Jupiter's 150 mile atmosphere are the oranges, reds and browns that we tend to associate with the planet. Since the clouds are closer to the surface, conditions here are very dark and much hotter.
Though we have long been mesmerized by these ever-shifting cloud formations, Jupiter's Great Red Spot has captivated astronomers for the opposite reason: an exception to the planet's constantly changing environment, the Great Red Spot does not change shape or location.
First spotted in the 17th century, this fascinating feature is an oval -- itself more than twice the size of Earth -- thought to be a gigantic, mighty hurricane. Though the Great Red Spot does not move or change shape, its strength does vary: sometimes, the Spot shrinks and becomes more faint, while other times it expands and becomes brighter and more intense.
Photo. The Great Red Spot, seen from Galileo on June 26, 1996. This image (a mosaic) was assembled from six pictures taken over 80 seconds as the spacecraft flew past. Courtesy NASA/Jet Propulsion Laboratory.
Covered by over one hundred miles of thick clouds, Jupiter's surface remains somewhat of a mystery. Astronomers believe that it is composed first of a deep liquid hydrogen ocean that covers the entire planet -- probably at a depth of 10,000 miles or more. It is quite likely that there is no solid surface until the rocky, iron core in Jupiter's center. The temperature at the core, which is buried 45,000 miles from the clouds, has been estimated at a sweltering 50,000 degrees Fahrenheit -- far from the -250 degree conditions near the tops of the clouds.
Jupiter's four largest moons, known as the Galilean moons, were named for their discoverer -- Italian scientist Galileo, who spotted them with a low-power "spy-glass" telescope in 1610. Our first close-up look at the moons came from the Voyager 1 space probe, which was launched in 1977.