Pluto: The First Dwarf Planet
	Pluto is actually smaller than one of Neptune's moons, Triton.

For many years, Pluto was thought of as the farthest known planet from the Sun. It has a very unusual orbit. Once every 248 Earth years, Pluto swings inside the orbit of Neptune. It stays there for twenty years. During those twenty years, Pluto is closer to the Sun than Neptune. While it is closer to the Sun, Pluto has an atmosphere. The methane and nitrogen frozen at the poles thaw out, rise, and temporarily form an atmosphere. As it moves toward its farthest point from the Sun, Pluto's atmosphere freezes and falls back to the ground. Since the year 2000, astronomers realized that Pluto was not like the other eight planets but very much like a new group of objects found in the outer solar system. In 2006, astronomers re-classified Pluto to be a dwarf planet. Pluto has three moons. Pluto's largest moon, Charon, is half the size of Pluto. In 2005, astronomers observed two more moons of Pluto. The moons were named Nix and Hydra.

A Question What are the names of Pluto's three moons?