Charon is composed mostly of water-ice. Although both Charon and Pluto are covered with ice, Charon's gray surface is less reflective and doesn't have any color. That's because Charon's surface is made of dirty water-ice. Pluto is 50 percent brighter than Charon.
Every 124 years (twice in Pluto's revolution around the Sun), Charon's orbit lines up directly in front of Pluto. This results in a cycle of eclipses that lasts several years. As Charon circles behind Pluto and back in front every six days, hundreds of eclipses occur. The last eclipse cycle occurred from 1985 to 1990. In the year 2109, the next cycle will begin.
