The Ice Planet
Pluto is smaller than one of Neptune's moons, Triton
Pluto is usually 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 nearer to the Sun than Neptune. While it is nearer to the Sun, 
Pluto has an atmosphere. The methane and nitrogen frozen at the poles form an atmosphere. 
Pluto has only one known moon. Pluto's moon, Charon, is half the size of Pluto. 
to the Solar System page