• Discovered: Prehistoric times
• Diameter: 143,000 km
• Temperature: -150 °C (in the atmosphere)
• Distance from the Sun: Varies between 740 - 817 million km

This enormous orange gas giant is made up of 90 per cent hydrogen. The atmosphere is not only poisonous, its pressure is so strong deep down that hydrogen gas is compressed into a liquid and any spacecraft would be crushed.

Although it takes 12 years to orbit the Sun, Jupiter only has a ten hour day. As a result, the planet rotates so fast that it produces violent winds, bulges 9,000 km at its equator and stretches the striped white clouds of ammonia ice. Its distinctive Red Spot is a 40,000 km storm system and could swallow the entire Earth.

Jupiter, with its many moons, is often compared to a miniature solar system. The astronomer Galileo discovered Jupiter’s four planet-sized moons in 1610. Today Io, Europa, Ganymede and Callisto are known as the Galilean satellites and are a source of great interest for space scientists.

Io is a volcanic minefield while Ganymede is the largest moon in our Solar System (it’s bigger than the planet Mercury) and is the only moon to have its own magnetic field. Meanwhile, Europa and Callisto may house a liquid ocean beneath their frozen crusts.

Jupiter also has a ring system. The Voyager 1 spacecraft first discovered a ring and subsequent Voyager 2 images found that it had three distinct components or bands, with the main ring thought to be formed by smashed meteoroids or the debris from small moons.

All eyes were on the planet in July 1994 when fragments of comet Shoemaker Levy 9 crashed into the planet producing fireballs and impact sites larger than the Earth.

There have been several recent visitors to Jupiter – including Ulysses en route to observe the Sun’s poles and Cassini during its highly successful mission to Saturn.

Galileo was the first spacecraft to orbit Jupiter and the last dedicated mission to the planet. It arrived at Jupiter in December 1995 after a six year journey. It also sent the first probe into Jupiter’s atmosphere and beamed back unprecedented information about wind speeds, temperature and pressure, studying the planet as well as its larger moons.

UK scientists from Oxford University, Imperial College London and the Open University were involved in three of the 11 instruments onboard Galileo, contributing greatly towards the mission’s success.

In 2003, after 14 years and 4.6 billion km later, Galileo made its final journey. It was sent plunging into Jupiter’s atmosphere and vaporised.