Improved Orbital and Physical Parameters for the Pluto-Charon System

Analysis of the observations of several Pluto-Charon occultation and transit events in 1985 and 1986 has provided a more detailed knowledge of the system. The sum of the radii of Pluto and Charon is 1786 $\pm $ 19 kilometers, but the individual radii are somewhat more poorly determined; Pluto is 1145 $\pm $ 46 kilometers in radius and Charon is 642 $\pm $ 34 kilometers in radius. The mean density of the system is 1.84 $\pm $ 0.19 grams per cubic centimeter, implying that more than half of the mass is due to rock. Charon appears to have hemispheres of two different colors, the Pluto-facing side being neutral in color and the opposite hemisphere being a reddish color similar to Pluto.