Diameter: 88,730 miles (142,796 km).

Mass: 317.8 Earth masses

Rotation period: 0.41 days.

Inclination of equator to orbit: 3.1 degrees.

Mean orbital speed: 8 Miles per second (13 km/s)

Mean distance from the sun: 485 million miles (778 million km)

THE STRUCTURE OF JUPITER

Jupiter is the fourth brightest object in the sky, and Galileo's discovery that four points of light (the four Galilean moons) rotated around the planet disproved the theory that everything revolved around the earth. It was a major finding in the supporting of the Copernicus heliocentric theory of the motions of the planets.

Jupiter's equatorial diameter, 88,846, is 11 times that of the earth. It is 317 times as massive as the earth and twice as big as all of the other planets in our solar system combined...with a gravitational pull second only to the sun. These startling figures begin to give us a picture as to the sheer size and presence of Jupiter within our solar system. Jupiter is approximately 485 million miles from us, and we have had to wait for the space age to see it up close, with its complex atmosphere, diverse retinue of moons and even a faint ring system. There have been fly byes (pioneer 10 in 1973, and Pioneer 11 in 1974) and visits to this colossal planet (Voyager 1 in 1979, and Voyager 2 a few months later), generating many images of the planets atmospheric features and its four largest satellites.  However it was Galileo, which arrived in 1995, which has provided us with the most telling evidence to date. This included eye opening images of Jupiter's surface, the surface of its satellites, and it also gave the first directly obtained data of the physical and chemical nature of the planets gaseous upper layers by deploying a probe into Jupiter's atmosphere.

Crossing Jupiter's surface are both bright and dark streaks, which are known as zones and belts respectively. They are essentially long lasting features which have remained at the same attitudes for at least a hundred years. These zones and belts are created by jets of wind circulating in alternating directions. The Galileo space probe found the winds on the planet to blow at speeds of around 400 miles per hour, and furthermore such winds may extend thousands of miles below the cloud tops. These winds may be driven by convection currents produced by an internal energy source....afterall it radiates twice as much energy as it receives from the sun because it is still cooling off from its formation.  The clouds markings are a result of chemical reactions and are also related to the clouds altitudes. Blue clouds lie deepest within the atmosphere, while brown and white clouds occur higher up. Rust coloured clouds are highest of all, and could be coloured by traces of phosphorous brought up by convection from Jupiter's interior.

As a gas giant Jupiter's structure and composition are radically different to those of the terrestrial planets. The atmosphere consists of 86% hydrogen and 14% helium, with traces of methane, water and ammonia. This mixture is thought to be much like the composition of the solar nebula, from which the solar system formed. Just beneath the cloud top is a layer of hydrogen gas. Some 600 miles below this, the hydrogen becomes liquefied, a point which marks the boundary between the planets outer atmosphere  and its interior. At a depth of between 16,000 and 19,000 miles, and under an estimated 4 million bars of pressure, the hydrogen becomes metallic, and can conduct electricity. It is thought that this is what generates Jupiter's powerful magnetic field, 20,000 times stronger than the earths. In the upper atmosphere temperatures are about –162 Fahrenheit , yet at the planets centre, which may be that of a rocky core,  temperatures increase to 40,000 Fahrenheit.

One other startling fact is that Jupiter is actually slowing down due to the tidal drag produced by the Galilean satellites. However the same tidal forces are changing the orbits of the moons, very slowly forcing them further away from the gas giant.

THE GREAT RED SPOT

Of all the cloud formations on Jupiter, the most renown has to be the large red spot which has been observed for more than 300 years. It varies in size, colour and intensity, and at its largest is 25,000 miles long and 8,700 miles wide. Infra red observations and the direction of its rotation indicate that the spot is a high pressure region whose cloud tops are significantly higher and colder than the surrounding regions.

RINGS AND MOON

Jupiter's ring was discovered by Voyager 1 in a single image that was targeted specifically to search for a faint ring system. Subsequently Voyager 2 was reprogrammed to take a more complete set of images. The ring is now known to be composed of three major components. The main ring is about 7000km wide and has an abrupt outer boundary. The main ring encompasses the orbits of two small moons, Adrastrea and Metis, which may act as the source for the dust that makes up most of the ring. At its inner edge the main ring merges gradually into the halo. The halo is a broad, faint torus of material about 20,000 km thick and extending halfway from the main ring down to the planets cloud tops. Just outside the main ring is the broad and exceedingly faint gossammer ring, which extends out beyond the orbit of the moon Amalthea.

Jupiter's ring is probably composed of dust particles less than ten microns in diameter, about the size of cigarette smoke particles. The origin of the ring is probably from micro–meteorite bombardment of the tiny moons orbiting within the ring.

The four largest of Jupiter's known 60 moons – Calisto, Ganymede, Io and Europa – were discovered in 1610 by Galileo, and referred to as the Galilean satellites. Ganymede and Calisto are larger than mercury and Pluto, whilst Europa and Io are similar in size to our moon. It is also interesting to note that Io, Europa and Ganymede are locked together in a 1:2:4  orbital resonance and their orbits evolve together. In a few hundred million years Calisto will be locked in too, orbiting at exactly twice the period of Ganymede. Below is a list of some of Jupiter's satellites, please click on the links to look at each of the moons in more detail....

SATELLITE

DISTANCE (KM)

RADIUS (KM)

MASS (KG)

Metis

128

20

9.56

Areas

129

10

1.91

Amalthea

181

98

7.17

Thebe

222

50

7.77

Io

422

1815

8.94

Europa

671

1569

4.80

Ganymede

1070

2631

1.48

Callisto

1883

2400

1.08

Leda

11094

8

5.68

Himalia

11480

93

9.86

Lysithea

11720

18

7.77

Elara

11737

38

7.77

Ananke

21200

15

3.82

Carme

22600

20

9.56

Pasiphae

23500

25

1.91

Sinope

23700

18

7.77

Callirrhoe

24,200,000

10

Chaldene

23,179,000

3.8

Erinome

23,279,000

3.2

Harpalyke

21,105,000

4.3

Locaste

21,269,000

5.2

Isonone

23,217,000

3.8

Kalyke

23,583,000

5.2

Magaclite

23,806,000

5.4

Praxidike

21,147,000

6.8

Taygete

23,360,000

5.0

Themsito

7,507,000

8.0

Euporie

Kale

Orthosie

Thyone

Euantha

Hermippe

Eurydome

Aitne

Sponde

Autonoe