It probably consists of a core of icy rock covered by a thick layer of water ice . The surface is reddish in color and contains frozen methane , nitrogen and carbon monoxide. There is a thin atmosphere. The following information was kindly contributed by Russell Odell. Pluto is the black sheep of the solar system.
Astronomers ignore it.
It is the only planet in the solar system that lacked the importance of being visited by a space probe. Charon is about half the size of the planet. Moons are always much smaller than the planet they orbit. As an example, our moon is about one fourth the size of our earth. The moons of Jupiter, Saturn and Neptune are much smaller than their respective planets.