General Information

Jupiter is the fifth planet from the Sun and the largest in the solar system. It is more than 10 times the diameter of Earth and more than 300 times its mass. In fact, the mass of Jupiter is almost 2.5 times that of all the other planets combined. Being composed largely of the light elements hydrogen and helium, its mean density is only 1.314 times that of water. The mean density of Earth is 5.245 times that of water. The pull of gravity on Jupiter at the top of the clouds at the equator is 2.4 times as great as gravity's pull at the surface of Earth at the equator. Jupiter rotates at a dizzying pace -- once every 9 hours 55 minutes 30 seconds, although the period determined by watching cloud features differs by up to five minutes due to intrinsic cloud motions. The massive planet takes almost 12 Earth years to complete a journey around the Sun. From the Earth, Jupiter can be seen to show a disc with polar flattening, this is due to a very rapid rotation.

Jupiter has a Great Red Spot (GRS), an enormous anti-cyclonic system which has lasted for hundreds of years. This hurricane-like storm in Jupiter's atmosphere is more than twice the size of the Earth. As a high-pressure region, the Great Red Spot spins in a direction opposite to that of low-pressure storms on Jupiter; it is surrounded by swirling currents that rotate around the spot and are sometimes consumed by it. Across the disc several bands of dark and light clouds can be seen and the GRS is visible during each rotation. Pictures returned by the Voyager probes have shown the complexity of the structures within these bands. It is thought that the brighter zones are cloud-covered regions of upward moving atmosphere, while the darker belts are the regions of descending gases. An elongated yellow cloud within the GRS is swirling around the spot's interior boundary in a counter-clockwise direction with a period of a little less than six days, confirming the whirlpool-like circulation that astronomers have suspected from ground-based photographs.

In 2006, another "red spot" was observed to have formed. At about one half the diameter of the Great Red Spot, the smaller version is perhaps evidence of a major climactic change currently occuring on Jupiter. Three small white storm systems merged together and in December of 2005 turned brown. In February of 2006 it was arguably Red.

Our spacecraft have detected lightning in Jupiter's upper atmosphere and observed auroral emissions similar to Earth's northern lights at the Jovian polar regions. Voyager 1 returned the first images of a faint, narrow ring encircling Jupiter. With 16 known moons, Jupiter is something of a miniature solar system. Already, several flyby missions of Jupiter and its moons have revealed much information about the Jovian system.

From July 16 through July 22, 1994, pieces of an object designated as Comet P/Shoemaker-Levy 9 collided with Jupiter. This was the first collision of two solar system bodies ever to be observed, and the effects of the comet impacts on Jupiter's atmosphere have been simply spectacular and beyond expectations. Comet Shoemaker-Levy 9 consisted of at least 20 discernible fragments with diameters estimated at up to 2 kilometres.