Pluto Discovered!

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid owing to the discovery that it is only one of several large bodies within the Kuiper belt.
Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small, approximately one-sixth the mass of the Earth's Moon and one-third its volume.

From its discovery in 1930 until 2006, Pluto was classified as a planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's relatively low mass, its status as a major planet began to be questioned. This definition excluded Pluto as a planet and added it as a member of the new category 'dwarf planet' along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and given the number 134340.