Jupiter

JUPITER

Distance from Sun 778.3 million km (483.7 million miles, 5.20 AU) 
Equatorial diameter 142,984 km (88,864 mi.) 
Equatorial diameter (Earth=1) 11.209 
Mass (Earth=1) 317.9 
Mean density 1.3 g/cm3
The largest planet in the Solar System and the fifth in order from the Sun. Jupiter is a gas giant, with 11 times the diameter of Earth, and two and half times the mass of all the other planets and satellites combined. It has an extensive family of satellites and a faint ring system. In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular results. Jupiter's immense atmosphere consists of about 75% hydrogen and 25% helium by mass (90% hydrogen and 10% helium by number of atoms), with trace amounts of methane, ammonia, and other light substances. The upper atmosphere is striated into wide parallel bands at different latitudes because of a combination of the planet’s rapid rotation and extensive convection caused by internal heat rising to the surface. Winds of more than 600 km/h blow in opposite directions in adjacent bands, while slight chemical and temperature differences between the bands are responsible for their different shades of yellow, brown, orange, and red. The light-colored bands are referred to as zones and the dark ones as belts. The zones are at a slightly higher altitude and about 15 K cooler than the belts. Complex vortices in the boundary regions between the bands were first seen by Voyager. The Galileo spacecraft's small descent probe also found turbulence in the Jovian atmosphere, indicating that Jupiter's winds are driven largely by the planet's internal heat rather than by solar radiation as on Earth. The colors of the surface gases are believed to be due in part to the release of phosphorous and the formation of acetylene. The colors correlate with the cloud's altitude: blue lowest, followed by browns and whites, with reds highest. Sometimes we see the lower layers through gaps in the upper ones. An enormous elliptical region in Jupiter's South Equatorial Belt, known as the Great Red Spot, is though to be a centuries'-old cyclone. Other similar but smaller and less long-lived spots have been known for decades. Intense lightning and powerful aurorae are other features of the jovian atmosphere. Jupiter spins around on its axis once every 9.8 hours (Jupiter's "day"). This is so fast, given Jupiter's size and the fact that it mostly a fluid, that Jupiter is noticeably squashed at its poles. Measuring longitude values on Jupiter is complicated by the fact that the planet spins more rapidly near the equator than it does at the poles. Three systems are used. Jupiter System I is used for features within about 10° of the equator, where a full rotation takes about 9h 50.5m. Jupiter System II is used for features north and south of this zone (such as the Great Red Spot), where a rotation takes about 9h 55.7m. Finally, Jupiter System III, which is based on the rotation of Jupiter’s interior, is used for radio observations and isn't particularly useful for visual observers. This rotation time of 9h 55.5m probably reflects the rate at which the solid core of Jupiter rotates, far below the cloud layers. Jupiter radiates about 2? times more heat than it receives from the Sun, indicating a substantial source of internal heat, almost certainly gravitational contraction, to account for the surface temperature. At its center, Jupiter is thought to have solid metal-rock core, similar in composition to Earth, with a diameter of about 24,000 km and a mass of 10 to 15 Earth-masses. Surrounding this, out to a diameter of about 100,000 km, is a metallic mixture of hydrogen and helium. On Earth we know these two as gases; in Jupiter's interior the pressure is so high that the hydrogen takes up a state in which it behaves like a metal. Outside this metallic hydrogen zone is a shell of liquid molecules, mainly hydrogen and helium, with the cloudy atmosphere, richer in ammonia and methane, about 1,000 km deep, above. Temperatures range from -130°C at the top of the clouds, to 30°C about 70 km below, to perhaps 20,000 K at the planet's center.