Possible Origin and Early Dynamical Evolution of the Pluto-Charon Binary

Abstract

The dynamical state of the Pluto-Charon binary is distinctive in several respects including its well-known position in the Neptune 3:2 mean motion resonance, its librating argument of perihelion, and its high heliocentric eccentricity and inclination. Here we present a suite of numerical simulations of bodies in the outer Solar System which demonstrate that Pluto's high-heliocentriceccentricity and high-inclination states can both result directly from objects initially on low-inclination, nearly-circular orbits. This evolution occurs entirely due to gravitational interactions with the giant planets in their present orbits and causes objects to be trapped in both the Neptune 3:2 mean motion resonance and a perihelion libration similar to Pluto's, but with a 3:2 libration amplitude that is much larger than that of the Pluto-Charon binary. Therefore, in order to achieve a complete scenario for the evolution of Pluto into its present dynamical state, it is also necessary for Pluto's 3:2 libration amplitude to be damped by some dissipative event or events. We show that there are several mechanisms that can achieve this dissipation including (i) a single giant impact (which may have formed the binary itself), or (ii) a large number of physical collisions and gravitational interactions with the primordial Kuiper belt population.