Tidal evolution of the Pluto-Charon binary

TL;DR

This paper models the tidal evolution of the Pluto-Charon system, considering a 3D approach and the influence of the Sun, revealing how initial conditions affect the system's eccentricity and stability over time.

Contribution

It introduces a comprehensive 3D model for binary tidal evolution, applying it to Pluto-Charon and exploring the effects of initial obliquity and solar perturbations.

Findings

High eccentricity is prevented by Sun's influence via Lidov-Kozai cycles.

High initial obliquity or spin-orbit capture dampens eccentricity efficiently.

The system can sustain moderate eccentricity despite strong tidal dissipation.

Abstract

A giant collision is believed to be at the origin of the Pluto-Charon system. As a result, the initial orbit and spins after impact may have substantially differed from those observed today. More precisely, the distance at periapse may have been shorter, subsequently expanding to its current separation by tides raised simultaneously on the two bodies. Here we provide a general 3D model to study the tidal evolution of a binary composed of two triaxial bodies orbiting a central star. We apply this model to the Pluto-Charon binary, and notice some interesting constraints on the initial system. We observe that when the eccentricity evolves to high values, the presence of the Sun prevents Charon from escaping because of Lidov-Kozai cycles. However, for a high initial obliquity for Pluto or a spin-orbit capture of Charon's rotation, the binary eccentricity is damped very efficiently. As a result, the system can maintain a moderate eccentricity throughout its evolution, even for strong tidal dissipation on Pluto.