Jupiter

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 143,000 kilometres (89,400 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 vapour 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.

Colourful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The Great Red Spot is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the centre, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found through out the banded clouds.

Auroral emissions, similar to Earth's northern lights, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from Io that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed.

Jupiter's Ring

Unlike Saturn's intricate and complex ring patterns, Jupiter has a single ring that is almost uniform in its structure. It is probably composed of dust particles less than 10 microns in diameter -- about the size of cigarette smoke particles. It extends to an outer edge of about 129,000 kilometres (80,161 miles) from the centre of the planet and inward to about 30,000 kilometres (18,642 miles). The origin of the ring is probably from micrometeorite bombardment of the tiny moons orbiting within the ring.

Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the Jovian magnetosphere or magnetic environment, which extends 3 to 7 million kilometres (1.9 to 4.3 million miles) toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit - a distance of 750 million kilometres (466 million miles).

Jupiter Statistics:

Time taken to orbit the Sun in Earth years: 11.86
Average orbital velocity in miles/second (km/sec): 8.1 (13.1)
Angle between orbit of planet and orbit of Earth: 1.30º
Time taken to rotate on axis in Earth time: 9hr 55min
Tilt of axis to perpendicular of orbital plane: 3º
Average distance from Sun in astronomical units*: 5.20
Average distance from Sun in miles (km): 480 million (778 million)
Average surface temperature in degrees Celsius: -123º (at cloud tops)
Density relative to water: 1.3
Equatorial diameter relative to Earth diameter**: 11.2
Equatorial diameter in miles (km): 89,400 (143,000)
Mass relative to Earth: 318
Escape velocity in miles/second (km/sec): 37.06 (59.64)
Number of known moons: 16
Number of known rings: 1
* One astronomical unit is 92,956,000 miles (149,598,000km)
** Earth's diameter is 7,926 miles (12,756km)