The largest moon of Pluto, Charon, was discovered in 1979. Charon is in a circular orbit of radius 19,600 km around Pluto and has an orbital period of 6.39 days. (By comparison, the Earth's moon has an orbital period of 27.32 days, and an orbit size of 384,400 km.) What is the total mass of the Pluto-Charon system?