Most of the time, the planet Pluto orbits behind the planet Neptune. Because of its small size it is now classified as a "dwarf planet". It is smaller than the seven moons of our solar system. Pluto was reclassified on August 24, 2006.
Pluto was discovered by an unusual accident in 1930 by Clyde W. Tombaugh at Lowell Observatory. The Lowell Observatory is based in Arizona. Tombaugh was basing his search on calculations that were incorrect, but ironically he found Pluto in spite of this.
No spacecraft has as of yet visited Pluto. In January of 2006 a spacecraft called New Horizons was launched and if it continues its journey uninterrupted it should reach Pluto by the year 2015.
In 1978 it was discovered that Pluto had a satellite. Its name is Charon. In 2005 two additional moons were found orbiting Pluto. They are very small. The Hubble Space Telescope was used to find the moons. The moons are known as Nix and Hydra. They are between 50 and 60 kilometers in diameter. While the total of the two masses (Pluto and Charon combined) are pretty well known. It is more difficult however to figure their individual mass because they are so small and far away. This makes it hard to decide which one is which at this distance.
Pluto is the second most contrasty body in the universe. This means it shows sharp contrasts between light and dark.
Pluto's orbit is considered to be unusually erratic. It sometimes orbits closer to the sun than Neptune. Pluto also orbits in the opposite direction than most of the other planets.
It takes 248 years for Pluto to orbit the sun. This means that since it wasn't discovered until 1930. This also means it will have to orbit for another 167 years to complete one orbit around the sun from the time of it's discovery.
Pluto is only about two thirds the diameter of Earth's Moon. It most likely has a rocky core surrounded by ice. Pluto is extremely cold. It is around -233 degrees C. At this temperature the only things that could survive on the tiny planet and remain unfrozen are neon, hydrogen and helium.
Since Pluto has the second slowest orbit of all the planets, a day of Pluto lasts for 6 days and nine hours in Earth time.
If Pluto were any closer to the sun it would be considered a comet.
Pluto is an interesting part of the Solar System and when the spacecraft makes a landing there perhaps it will become even more so.