Jupiter is the largest planet in the Solar System and is the innermost of the gas giants. Named after the Roman King of the Gods the planet is located beyond the asteroid belt. Jupiter orbits between 740 million and 778 million km from the Sun and is primarily composed of hydrogen and helium. It is the fourth brightest object in the sky behind the Moon, Sun and Venus and has an extremely fast rotation period, completing one every ten hours. The planet takes eleven years to complete an orbit of the Sun.



Jupiter is quite unlike Earth and its neighbours as it is mostly composed of gases rather than heavier elements. Jupiter is two and a half times more massive than all the other planets put together and is about as large as a planet of its type can grow. If it were to take on more mass the diameter would actually decrease from the increased gravity. If it were 75 times larger then it would be able to fuse hydrogen and become a star, this has lead some astronomers to label the planet as a failed star. However despite its humble status as a planet Jupiter does create a substantial amount of its own heat, generating more than it receives from the Sun.

The atmosphere of Jupiter is made of many distinctive bands of gas and light elements. Different areas of the planet have been shown to rotate at different speeds, and there are many storms present. The most notable storm on Jupiter is the Great Red Spot. This giant anomaly on the surface of the planet is larger than Earth and is a storm that has been raging ever since we first discovered the planet. Jupiter is peppered with similar storms and recently three large grey ones merged into one storm, similar to the red spot.

Jupiter has only been explored by automatic deep-space probes, there is no surface to land on and there have been no landings on any of its moons yet. The first probe to fly-by Jupiter was the Pioneer 10 in 1973. Pioneers 10 and 11 would gather a multitude of images and date about the planet, detecting the magnetic field and radiation belts. In 1979 Voyagers 1 and 2 passed Jupiter followed by Ulysses in 1992. The only probe to orbit Jupiter is the Galileo spacecraft, which reached the gas giant in 1995. The craft stayed in orbit for seven years, releasing an atmospheric probe in July 1995. The probe descended into Jupiter and sent back data for 57 minutes before it was crushed by the pressure. Eventually Galileo was sent into the planet in order to prevent it crashing into and contaminating any of Jupiter's moons.

Jupiter has 63 moons, some of which are among the largest objects in the Solar System. The four largest are Io, Callisto, Ganymede and Europa, known as the Galilean moons after their discoverer Galileo. The moons of Jupiter are among the most interesting bodies in the Solar System with some striking geological activity and possible sites for life. The moon Europa may be the site of a liquid ocean underneath its icy crust and is a place that scientists are extremely interested in exploring. The moons of Jupiter are not as cold and lifeless as they may be otherwise due to tidal flexing providing friction on the inside of the planet and keeping them active. Io is the most geologically active body in the Solar System with over 400 volcanoes, Ganymede is the largest non-planet and Callisto is considered a possible site for extra-terrestrial microbial life.

Jupiter is not as openly considered for colonisation as our nearby planets Mars and Venus. The giant planet does however offer an inviting location for a stepping stone into the outer Solar System. Its many moons could make good places for colonies and may even provide economic benefits through mining. The future will see further missions to the moons to look for signs of life and liquid oceans.