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Jupiter is named for the mythological king of the gods, known in Greek as Zeus. The son of Cronus, Jupiter was considered ruler of Olympus and patron of the Roman state. A great deal of what we know about the planet Jupiter can be traced back centuries ago, to the pioneer astronomer Galileo Galilei (1564-1642). Without the high-tech tools we possess today, Galileo was able to ascertain some of the unique features of the solar system’s largest planet. The fifth planet from the sun, Jupiter is orbited by 39 moons, but only four have substantial size: Ganymede, Callisto, Is, and European, which together are known as the Galilean Satellites, named in honor of the man who discovered them in 1610.
Jupiter is referred to as a “gas giant”; it is eleven times wider than Earth. The planet is virtually all atmosphere, with a comparatively small solid core. Jupiter’s atmosphere consists mainly of hydrogen and helium with droplets of ammonia forming the upper clouds. The visible surface shows evidence of distinct weather systems. Jupiter is perhaps best known for its Great Red Spot, which is actually a huge storm system, larger than Earth, rotating every dozen days. In addition, bands signifying the different currents occurring in the atmosphere are readily apparent. These bands rotate with Jupiter, with the equatorial regions moving faster than the polar regions.
Many of Jupiter’s moons are quite small-one is only ten kilometers wide, making it possibly the tiniest moon circling any of the gas giants. Scientists continue to unlock the secrets of this unique planet. As recently as May of 2002 astronomers detected Jupiter’s 39th satellite. The planet also has a ring system which is not visible from Earth which was first discovered in pictures taken by the Voyager probe.
Because of Jupiter’s size, there is a great deal of pressure at its core which, in turn, yields significant amounts of heat and radiation. In fact, its core may be as hot as 30,000 degrees C. Furthermore, the environment surrounding Jupiter can be disastrous for spacecraft that venture too close; radiation belts extending from the planet into space can make the surrounding area unbearable. The planet is believed to be 90 percent hydrogen and ten percent helium, with traces of methane, water, ammonia, and rock. Jupiter radiates more energy into space than the sun provides to the planet.
If Jupiter had been more massive, it would have actually been a star. The planet is also noteworthy for the strong magnetic field it produces. On July 18, 1994, nineteen fragments of the comet Shoemaker-Levy collided with Jupiter, in collisions that were more destructive than atomic bombs. When the comet crashed into the planet, scientists believe it marked the first time such an event had been witnessed in the solar system.
The first spacecraft to visit Jupiter was the Pioneer 10 in 1973. Subsequently, Jupiter was visited by Pioneer 11, Voyager 1, Voyager 2, and Ulysses. The Galileo probe is currently in orbit around Jupiter and will be sending back information to scientists on Earth in the next two years.
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