From Encyc

Pluto is a Trans-Neptunian object, the first to be identified in history. It was discovered in 1930 by Clyde Tombaugh.

It was considered as the ninth and last planet, lying beyond Neptune. However, the formal definition of a planet introduced by the International Astronomical Union in 2006 resulted in Pluto losing its status and becoming a dwarf planet. It is very small, rocky, and cold, because it receives little light from the Sun.

It has three satellites. Charon is the biggest, about half its size, and the first to be discovered. The other two are Nix and Hydra.