Bulk Properties of Pluto and Charon.

D. J. Tholen and M. W. Buie. In Pluto and Charon (D. J. Tholen and S. A. Stern, eds.) UA Press, Tucson, AZ (1997) .


Much of what we can deduce about the origin and evolution of the Pluto-Charon system, and its implications for the outer Solar System, depends on our knowledge of the bulk properties of the two bodies. In this chapter, we review the inventory of the system, the orbits of the two bodies, their rotational states, sizes, masses and densities, other global surface characteristics, and their atmospheres. Historically significant improvements to these various parameters are mentioned, and we attempt to assess the reliability of the latest values and reach a consensus where possible. Key quantities include a 6.38726 +/- 0.00007 day rotational period for Pluto, a 6.387223 +/- 0.000017 day orbital period for Charon, an orbital semimajor axis of 19,636 +/- 8 km and significant nonzero eccentricity for Charon, a system mass of 0.002433 +/- 0.000003 Earth masses, a consensus Charon/Pluto mass ratio of 0.119 +/- 0.005, a Pluto radius between 1145 and 1200 km, a Charon radius between 600 and 650 km, a system mean density between 1.87 and 2.03 g cm-3, a Pluto density between 1.92 and 2.06 g cm-3, and a Charon density between 1.51 and 1.81 g cm-3. The surface composition of Pluto includes the spectroscopically detected ices of water, nitrogen, methane, and carbon monoxide, whereas only water ice has been detected on Charon. The composition of Pluto's atmosphere is apparently dominated by nitrogen, with much smaller amounts of methane and carbon monoxide; no detectable atmosphere has been found around Charon.

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