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| Quick Facts
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Mass : 1.90 x 10^27 kg
Diameter : 142,800 km (88,731.8 miles)
Mean density : 1,314 kg/m^3
Escape velocity : 59,500 m/sec
Average distance from Sun : 5.203 Astronomical Units
Rotation period/Length of Day : 9.8 Earth hours
Revolution period/Length of Year: 11.86 Earth years
Obliquity/Tilt of Axis : 3.08 degrees
Orbit inclination : 1.3 degrees
Orbit eccentricity (deviation from circular): 0.048
Mean surface temperature : 120 K (cloud tops)
Visual geometric albedo (reflectivity): 0.44
Rings: Faint ring : Infrared spectra imply dark rock fragments.
Halo
Distance (From center of Jupiter) : 92,000 km (57,166.15 miles)
Width: 30,500 km (18,951.82 miles)
Thickness: 20,000 km (12,427.42 miles)
Main
Distance (From center of Jupiter) : 122,500 km (76,117.97 miles)
Width: 6,440 km (4,001.63 miles)
Thickness: Greater than 30 km (18.64 miles)
Inner Gossamer
Distance (From center of Jupiter) : 128,940 km (80,119.60 miles)
Width: 52,060 km (32,348.58 miles)
Thickness: Unknown
Outer Gossamer
Distance (From center of Jupiter) : 181,000 km (112,468.18 miles)
Width : 40,000 km (24,854.84 miles)
Thickness : Unknown
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| The Gas Giant
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Jupiter is the fifth planet from the Sun and is the largest one in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains more matter than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 16 satellites, four of which - Callisto, Europa, Ganymede and Io - were observed by Galileo as long ago as 1610. There is a ring system, but it is very faint and is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager 1.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen becomes metallic. Its core may be as hot as 54,000 degrees Fahrenheit (30,000 C).
Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and Venus; at some times Mars is also brighter). It has been known since prehistoric times.
Jupiter is a "gas giant"; all gas giants are similar to Jupiter in composition. Jupiter's diameter is 11 times Earth's diameter and 20% larger than Saturnšs, making it the largest planet in the solar system. Gas giants are also very much larger than terrestrial planets.
The gas planets do not have solid surfaces; their gaseous material simply gets denser with depth (the radii and diameters quoted for the planets are for levels corresponding to a pressure of one atmosphere). A vast ocean of liquid hydrogen may lie beneath the clouds, with a solid core probably 10 to 20 times as massive as Earth.
What we see when looking at these planets is the tops of clouds high in their atmospheres (slightly above the one atmosphere level).
Jupiter is about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass) with traces of methane, water, ammonia and "rock". Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.
Jupiter and the other gas planets have high velocity winds, which are confined in wide bands of latitude. The winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences between these bands are responsible for the colored bands that dominate the planet's appearance. The light colored bands are called zones; the dark ones are called belts. The data from the Galileo probe indicate that the winds are even faster than expected (more than 400 mph) and extend down into as far as the probe was able to observe. Jupiter's atmosphere was also found to be quite turbulent. This indicates that Jupiter's winds are driven in large part by its internal heat rather than from solar input as on Earth.
Unlike Saturn's intricate and complex ring patterns, Jupiter has a simple ring system that is composed of an inner halo, a main ring and a Gossamer ring. To the Voyager spacecraft, the Gossamer ring appeared to be a single ring, but Galileo imagery provided the unexpected discovery that Gossamer is really two rings. One ring is embedded within the other. The rings are very tenuous and are composed of dust particles kicked up as interplanetary meteoroids smash into Jupiter's four small inner moons. Many of the particles are microscopic in size.
In addition, Jupiter's rings are dark (albedo about .05). Unlike Saturn's rings, they seem to contain no ice.
The temperature on Jupiter varies widely depending on the depth below the top of the atmosphere, ranging from much hotter to much colder than any place on Earth. Humans will probably never visit Jupiter. It is possible that some form of life may exist there, although it would be very different from life on Earth.
| Great Red Spot
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The solar system's best-known hurricane is Jupiter's Great Red Spot. It was first seen in 1664, although it surely existed even before then. In more than 300 years of observations, its size and color have varied, but it's never disappeared.
The Great Red Spot is a storm befitting the solar system's largest planet. It's wide enough to swallow three Earths, and winds reach 1,000 miles an hour at the storm's rim.
The storm is driven by Jupiteršs internal heat. Relatively warm water and ammonia rise from far below Jupiteršs visible cloud tops, and spread out as they reach the upper atmosphere. Jupiteršs rotation causes the flattened cloud to spin rapidly -- up to a thousand miles an hour at its rim.
Despite decades of study, though, scientists arenšt sure why the storm is so big, so persistent, or so red. The other storms on Jupiter are much smaller, and are colored brown or white. They generally last from a few months to a few years. None has ever been this big or this red.
The Galileo spacecraft may provide new clues during its final year of operation. Or the Great Red Spot may keep its secrets until scientists can drop a probe into its clouds -- well into the next century. In 1989, the Voyager 2 spacecraft found another giant storm in the atmosphere of Neptune, another gas-giant planet. It was called the Great Dark Spot for its dark blue color.
Like the Great Red Spot, Neptune's Great Dark Spot was about twice is long as it was wide. The two storms were located at about the same latitudes, too south of their planets' equators.
But the Great Dark Spot has since disappeared. Like hurricanes on Earth, it blew itself out.
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