Where is the center of mass of the Pluto-Charon system located?
Pluto has a mass of 0.0024 Earth's. Its radius is 1151 kilometers.
Charon has a mass of 0.01 x Earth's Moon or 0.000123 Earth masses. Its
radius is estimated to be 600 kilometers at a distance of 19,700 kilometers
from Pluto. This would put the barycenter of this system at
19,700 x (0.000123/(0.0024+0.000123) = 19,300 kilometers from the center
of Charon along a line connecting their centers. This puts it
400 kilometers from the center of Pluto, or about
1151-400 = 751 kilometers beneath the surface of Pluto.
By comparison, the Moon-earth center is located
384,401 km x (0.0123/(1.0 + 0.0123) = 4670 kilometers from the center of the
Earth, or ( 6378 - 4670 ) = 1700 kilometers beneath the Earth's surface.