PlutoPluto is a distant, cold and icy world orbiting the Sun many millions of miles away from it in a region of the Solar System known as the Kuiper Belt. Smaller than several moons in the Solar System, including Earth's moon, Pluto is the most well-known of the Dwarf Planets. It is only 2,370 kilometres wide and takes 248 years to orbit the Sun.
Pluto was discovered in 1930 when astronomers were on the look-out for a mysterious "Planet X" after it was realised there must be something beyond Neptune which was affecting its orbit. Clyde Tombaugh found "Planet X", which was later named Pluto by a young English girl (after the Roman God of the Underworld, not Mickey Mouse's dog!).
After its discovery, Pluto became recognised as the ninth planet in the Solar System. It remained this way until August 2006 when scientists from all over the world voted for it to be reclassified as a Dwarf Planet mainly due to the fact that it orbits in a region of similar objects in the Kuiper Belt, beyond the orbit of Neptune. Added to this is the fact that, unlike the rest of the planets, which orbit in fairly circular orbits and on the same plane as each other, Pluto's orbit is elliptical and tilted. Its elliptical orbit means that, for a few years during each of its 248 year long journeys around the Sun, it is actually closer to it than Neptune!
Pluto has five moons orbiting it. Charon was discovered in 1978 and is almost as large as Pluto. The two objects appear to spin around each other, taking 6 days to complete a full orbit. If Pluto was still a planet, the two objects would probably be classed as "binary planets". Two smaller, irregularly-shaped moons, were also discovered in October 2005. These moons, named Hydra and Nix take 38 days and 25 days respectively to complete their orbits. A fourth moon, now named Kerberos, was discovered in 2011, and a fifth moon, Styx, was discovered in 2012. Pluto and other Kuiper Belt objects are due to be visited by NASA's New Horizons probe which was launched in January 2006 and should get there in 2015. This mission will hopefully finally reveal some of the secrets that Pluto, its moons, and other Kuiper Belt objects and Dwarf Planets currently hold!