Jupiter (astronomy)

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Fifth planet from the Sun and the largest in the Solar System, with a mass equal to 70% of all the other planets combined and 318 times as large as that of the Earth. A prominent feature is the Great Red Spot, a cloud of rising gases, 14,000 km/8,500 mi wide and 30,000 km/20,000 mi long, revolving anticlockwise.

Mean distance from the Sun
778 million km/484 million mi

Equatorial diameter
142,800 km/88,700 mi

Rotation period
9 hours 51 minutes

Year
11.86 Earth years

Atmosphere
consists of clouds of white ammonia crystals, drawn out into belts by the planet's high speed of rotation (the fastest of any planet). Darker orange and brown clouds at lower levels may contain sulphur, as well as simple organic compounds. Temperatures range from -140°C/-220°F in the upper atmosphere to as much as 24,000°C/43,000°F near the core. This is the result of heat left over from Jupiter's formation, and it is this that drives the turbulent weather patterns of the planet. The Great Red Spot was first observed in 1664. Its top is higher than the surrounding clouds; its colour is thought to be due to red phosphorus. The Southern Equatorial Belt in which the Great Red Spot occurs is subject to unexplained fluctuation. In 1989 it sustained a dramatic and sudden fading. Jupiter's strong magnetic field gives rise to a large surrounding magnetic ‘shell’, or magnetosphere, from which bursts of radio waves are detected. Jupiter's faint rings are made up of dust from its moons, particularly the four inner moons

Composition
largely hydrogen and helium, which under the high pressure and temperature of the interior behave not as a gas but as a supercritical fluid. Under even more extreme conditions, at a depth of 30,000 km/18,000 mi, hydrogen transforms into a metallic liquid. Jupiter probably has a molten rock core whose mass is 15 to 20 times greater than that of the Earth

In 1995, the Galileo probe revealed Jupiter's atmosphere to consist of 0.2% water, less than previously estimated.

Satellites
Jupiter has 28 known moons. The four largest moons, Io, Europa (which is the size of the Moon), Ganymede, and Callisto, are the Galilean satellites, discovered in 1610 by Galileo Galilei (Ganymede, which is larger than Mercury, is the largest moon in the Solar System). Three small moons were discovered in 1979 by the US Voyager probes, as was a faint ring of dust around Jupiter's equator 55,000 km/34,000 mi above the cloud tops. One of Jupiter's small inner moons, Amalthea (diameter 250 km/155 mi), was shown by pictures from the Galileo probe in April 2000 to have a long, narrow, bright region, as yet unidentified. A new moon was first observed orbiting Jupiter in October 1999 by US researchers at the Kitt Peak Observatory, Arizona. It was thought to be an asteroid and named S/1999J1, but was confirmed to be a moon in July 2000. The moon is only 5 km/3 mi in diameter and orbits Jupiter once every two years at a distance of 24 million km/15 million mi. Ten previously unobserved moons were discovered orbiting Jupiter in November and December 2000. These moons are all believed to be less than 5 km/3.1 mi in diameter, and were observed by astronomers at the Mauna Kea observatory, Hawaii.

The comet Shoemaker-Levy 9 crashed into Jupiter in July 1994. Impact zones were visible for several months.

Green expresses hope. White symbolizes peace. It is said that the saltire may have been based on the former flag of Belgian airline, Sabena. Red represents the blood shed in the struggle for independence. Effective date: 27 September 1982. >>