Masses and densities of Pluto and Charon

by: Null, G. W.; Owen, W. M., Jr.; Synnott, S. P.

ABSTRACT

We have analyzed HST Wide Field Camera CCD images of Pluto, Charon, and a
background star to observe Pluto's barycentric motion and to determine
the individual masses and bulk densities of Pluto and Charon. The most
fundamental new result was an accurate solution for a previously undeter-
mined parameter, the Charon Pluto mass ratio q the new solution is q =
0.0837 - 0.0147. Significant accuracy improvements by almost a factor of
two were obtained for Charon's orbital semimajor axis, a = 19,405 - 86 km
and the Pluto system mass of 1.401 - 0.019 x 10 exp 8 inverse solar masses.
The Pluto and Charon masses were (13.10 - 0.24) x 10 exp 24 g and (1.10 -
0.18) x 10 exp 24 g, respectively. Computed densities depend strongly on
the assumed radius values. The density of Pluto is 2.13 - 0.04 g cu cm
and that of Charon is 1.30 - 0.23 g cu cm.

Astronomical Journal vol. 105, no. 6 p. 2319-2335. June 1993