Transcript: Pluto's satellite Charon is half the size of Pluto itself. The ratio between the planet and its moon is the smallest in the solar system. Pluto rotates in 6.4 days, and the orbital period of Charon is the same number, 6.4 days. They are in a synchronous orbit and so always face each other. The density of Pluto is about 2000 kilograms per cubic meter which indicates that Pluto is composed roughly of 70 percent rock and 30 percent ice. The somewhat lower density of Charon indicates that it's more ice rich. The orbit of Charon and Pluto has been beautifully mapped out using the Hubble Space Telescope which can clearly resolve the two objects.