|Diameter||143000 km, 11 x Earth's|
|Mean Density||1.33 g/cm3|
|Mean Distance from Sun||788 x 106km = 5.203 AU|
|Eccentricity of Orbit||0.048|
|Inclination of Equator to Orbit||3.13°|
|Inclination of Orbit to Ecliptic||1.3°|
|Colour||Orangey-brown with white bands|
|Atmosphere||Hydrogen, ammonia and methane|
|Length of Day||10 hours|
|Length of Year||12 years|
|No. of Moons||16|
|Gravity||2.34 x Earth's|
|Escape Velocity||59.6 km/s|
Jupiter is the fifth planet from the Sun and is the first of the gas giants. It is the largest planet in the Solar System - so large that over 1300 Earths would fit inside it.
Jupiterís atmosphere is mainly hydrogen with ammonia and methane mixed in. It is these chemicals that give the planet its brown and white markings. The brown areas are regions of falling gas called bands, while the white areas are rising gas, called zones. The biggest feature on the surface of the planet is the Great Red Spot. This is a huge storm that has raged for hundreds of years. It is large enough to fit about 4 Earths inside it.
In 1994, pieces of the comet Shoemaker-Levy 9 crashed into Jupiter, allowing scientists to study the atmosphere. At least 21 pieces of the comet struck the planet, leaving marks on the surface that lasted for months. This was the first time anybody had ever seen a body from outer space collide with a planet.
Jupiter has the largest magnetic field of all the planets. It also radiates more energy than it receives from the Sun, meaning that it must have a faint internal heat source. The pressure at the centre of Jupiter is about 4 million times the pressure at the surface of Earth.
Jupiter and four of its moons, Ganymede, Europa, Callisto and Io can easily be seen through binoculars. They are called the Galilean moons because their orbits around Jupiter were first studied by Galileo. Jupiter also has very faint rings like Saturnís but they are made of much darker material so they are harder to see.
Jupiterís moons are also very interesting. Io is immensely volcanic because as it orbits the planet it is squashed and stretched by huge tidal forces. These are caused by the large gravitational pull of Jupiter. This squeezing and stretching heats up the inside just as a squash ball heats up if you squeeze it a lot. The rock in the centre of the moon then becomes molten and bursts out from the surface in huge eruptions that were photographed by the Galileo spacecraft.
Europa is thought to have a water ocean underneath its ice surface, making it one of the most likely places to find life in the Solar System. The dark lines across it's surface are believed to be cracks where the liquid ocean has welled up and burst out onto the surface. The ocean can stay liquid because it is warmed by the same tidal forces which heat up Io, but because Europa is further away, these forces are not so strong and the heating effect is therefore not quite so drastic. Research is currently being carried out to find a way to cut through the thick ice and send a spacecraft into this ocean to try to find life.
Authors: Carolyn Brinkworth and Claire Thomas
Last updated: July 2001