P41E-09
New Insights into the Structure, Origin, and Evolution of Pluto and Charon
Thursday, 17 December 2015: 09:42
2022-2024 (Moscone West)
William B McKinnon1, Alan Stern2, Harold A Weaver Jr3, John R Spencer4, Francis Nimmo5, Carey Michael Lisse3, Orkan M Umurhan6, Jeffrey M Moore7, Marc W Buie4, Simon Porter4, Catherine Olkin4, Leslie Ann Young4, Kimberly Ennico Smith8 and New Horizons Geology, Geophysics and Imaging Theme Team, (1)Washington University in St Louis, St. Louis, MO, United States, (2)Southwest Research Institute, Boulder, CO, United States, (3)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (4)Southwest Research Institute Boulder, Boulder, CO, United States, (5)University of California-Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA, United States, (6)SETI Institute Mountain View, Mountain View, CA, United States, (7)NASA Ames Research Center, Moffett Field, CA, United States, (8)NASA Ames Research Center, MS 245-3, Moffett Field, CA, United States
Abstract:
The July 2015 New Horizons flyby has removed a long-standing obstacle to understanding the cosmogony of the Pluto-Charon system: the uncertain radius of Pluto. Combined with precise astrometric fits to the barycenter of the Pluto-Charon binary from HST observations of the more distant, small satellites (M. Brozović et al., Icarus 246, 317–329, 2015), the densities of both Pluto and Charon are now known. At the 10% level, the densities of Pluto and Charon are rather similar, as opposed to the more divergent density estimates of years past in which Charon was thought to be substantially icier. In the context of a giant impact origin for binaries, a rock-poor Charon corresponds to an iron-poor Moon in the terrestrial case, with differentiated precursors being implied in both cases. A rock-rich Charon, however, implies that the precursor impacting bodies were at most only partially differentiated — possessing relatively thin ice shells (R.M. Canup, Astron. J. 141, 35, 2011). This suggests some combination of relatively slow and/or late accretion in the ancestral Kuiper belt. A more rock-rich Charon also implies a more vigorous geological history, all other things being equal. For Pluto, the evolution to the surface of a substantial mass of supervolatile ices increases the likelihood that internal volatiles such as ammonia and methanol have been sequestered in an internal, aqueous layer (or ocean).
