Pluto

Pluto is the second-largest known dwarf planet in the Solar System and the tenth-largest body observed directly orbiting the Sun. From the time of its discovery in 1930 by Clyde Tombaugh until 2006, Pluto was considered the Solar System's ninth planet; now recognised as the largest member of a distinct region called the Kuiper belt. It is primarily composed of rock and ice and is relatively small; approximately a fifth the mass of the Earth's Moon. Pluto has an eccentric orbit that takes it from 4.4-7.4 billion km from the Sun, and is highly inclined with respect to the planets. As a result, it occasionally comes closer to the Sun than Neptune. Pluto and its largest moon, Charon, are often considered a binary system. It has two known smaller moons, Nix and Hydra. Anxiously awaited follow-up observations with the NASA/ESA Hubble Space Telescope have confirmed the presence of these two new moons. The moons were first discovered by Hubble in May 2005.