Photo courtesy of NASA

by Alan Murphy and Timothy McCarthy

Jupiter is the fifth planet from the Sun, and the largest planet in the Solar System. Jupiter is almost big enough to be a star; with a diameter of 142,984 km, it is so large that all of the other planets in the Solar System could fit inside of it. Jupiter is a gas planet made of 90% hydrogen and 10% helium. The outermost layer is liquid in the interior and gaseous further in. Jupiter radiates twice the heat as it receives from the Sun. It has its own internal heat source; the temperature of its core or center is about 20,000 degrees Celsius, 3 times greater than the temperature of the Earth's core. Jupiter's interior pressure reaches 100 million times the pressure of Earth's surface.

Jupiter's magnetosphere reaches 650 million kilometres past the orbit of Saturn. Its magnetosphere is generated by the electric currents produced by pressurizing hydrogen in Jupiter's mantle or surface. Jupiter has 16 moons or natural satellites orbiting around it; these moons lie within its magnetosphere. Jupiter's moons are named after the figures in Zeus' life. One of these moons,Io is volcanically active. Jupiter and its moons are often likened to a mini-solar system.

The Galileo probe discovered a new intense radiation belt between Jupiter and the uppermost atmosphere layers. Jupiter has faint, thin rings much like Saturn, but much smaller. The rings were totally unexpected, and were confirmed by Voyager 2, a space probe after travelling 1 billion km. The majority of the rings are made up of very small particles thought to be debris from meteorite collisions. Unlike Saturn, Jupiter's rings are dark.

Jupiter's Great Red Spot, the most prominent hurricane-like storm of circular winds in Jupiter's atmosphere, has been seen by Earth for more than 300 years. Jupiter's Great Red Spot is oval and is 12,000 km wide by 25,000 km long, large enough to hold 2 Earths. The Great Red Spot of Jupiter rotates in a counter-clockwise direction every six days. The colors in Jupiter's clouds are probably the result of several chemical reactions. On Jupiter, the winds blow in opposite directions, the clouds moving in alternating bands from east to west or west to east. Jupiter and the other gas planets have high velocity winds. Lightning in Jupiter's atmosphere is more powerful than any that has been experienced on Earth.

Bibliography and Additional Sources of Information

Galileo Project: Journey to Jupiter.

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