134340 Pluto was formerly the ninth planet (or the first dwarf planet to be classified) from the sun. With the addition of Ceres, it is now the 2nd dwarf planet from the Sun.
Like other Dwarf Planets in the Kuiper Belt, Pluto has an orbit that is so tilted, that it crosses the orbit of Neptune and the other Plutoids (all 3 Kuiper Belt dwarfs have orbits that cross the orbit of Neptune). This was one reason Pluto was changed from a major planet to dwarf planet in 2006. Pluto has 5 moons. Discovered in 1978, Charon is the largest of Pluto's moons and is half the size as Pluto and thus, they have often been considered as a Double Dwarf planet, but the IAU has not yet classified them as a double Dwarf Planet.The other moons (Nix, Hydra, P4,P5) are very small.
Scientists think that Pluto is made of Ice and Rock. Its atmosphere contains Nitrogen and Carbon monoxide.
The naming of Pluto is a story by itself. Early suggestions of the name of the new planet were: Atlas, Zymal, Artemis, Perseus, Vulcan, Tantalus, Idana, Cronus. The New York Times suggested Minerva, reporters suggested Osiris, Bacchus, Apollo, Erebus. Lowell's widow suggested Zeus, but later changed her mind to Constance. Many people suggested the planet be named Lowell. The staff of the Flagstaff observatory, where Pluto was discovered, suggested Cronus, Minerva, and Pluto. A few months later the planet was officially named Pluto. The name Pluto was originally suggested by Venetia Burney, an 11-year-old schoolgirl in Oxford, England.
Voyagers 1 and 2 nor Pioneers 10 and 11 were able to meet Pluto. The New Horizons spacecraft was launched in 2006 and passed Jupiter in 2007. It is now heading for an encounter with Pluto and its moons, along with MakeMake. Its stop at Pluto is scheduled for July 2015.