• Discovered: 1781 by William Herschel from Bath, England
• Diameter: 51,499 km
• Temperature: -210 ºC (at cloud tops)
• Distance from the Sun: Varies between 2.7 and 3 billion km
• Satellites: 27

The third largest planet in the Solar System, Uranus is named after the Greek god of the heavens and was the first planet to be discovered through a telescope.

Uranus has a total of 13 rings and 27 known moons, all named after characters in works by William Shakespeare and Alexander Pope. A day on the planet lasts 17 hours while a year on Uranus is equivalent to 84 Earth years.

Structure

Uranus is referred to as an ‘ice giant’ and has no solid surface. Its atmosphere is made up of hydrogen (83 per cent) and helium (15 per cent) with small amounts of methane, water and ammonia.

The bulk of the planet's mass is contained in a liquid mantle surrounding a small, rocky core and Uranus’ blue colour results from methane in its atmosphere.

Winds in the upper atmosphere can blow up to 600 km per hour and, because it is so far away from the Sun, it takes Uranus 84 years to complete a single orbit. It also explains why the temperature near the cloud tops is a chilly -210º C.

Rotation

Unlike other planets in the Solar System, Uranus rotates as though it has been tipped on its side: the planet turns at right angles to its orbit around the Sun. This means that the rings and moons are also at right angles and circle Uranus like a target.

The result is that the poles experience periods of darkness and light lasting 42 years as the planet orbits the Sun. Scientists believe that Uranus is unlikely to have formed naturally this way. One suggestion for how this occurred is that it may have collided with another body.

Missions

Much of what we know about Uranus has been discovered relatively recently. The rings were identified in 1977 and only one spacecraft has passed close enough to observe the planet in detail.

In 1986, Voyager 2 came within 82,000 km of the planet’s cloud-tops and was able to send back thousands of images. The spacecraft can also lay claim to identifying 11 of the planet’s moons.

At present there are no firm plans for a return mission to this mysterious and intriguing planet.