Determination of commensurabilities in the dynamics of the Pluto-Charon's satellites

TL;DR

This study precisely identifies and analyzes the commensurabilities among Pluto-Charon's satellites using advanced frequency analysis, combining analytical and numerical methods to enhance understanding of their long-term dynamical behavior.

Contribution

It introduces a detailed frequency analysis approach to identify known and new commensurabilities in the Pluto-Charon satellite system, validating results with both analytical and numerical models.

Findings

Successfully identified all fundamental frequencies of the system.

Confirmed alignment of results with epicyclic analytical theory.

Discovered new commensurabilities and observed libration phenomena.

Abstract

The Pluto-Charon system is a binary system, characterised by its high mass ratio and its tidally locked synchronous orbit. Surrounding the central binary, four satellites - Styx, Nix, Kerberos and Hydra - follow near-circular and near equatorial orbits. Mutual tidal forces have probably a great influence on their long term dynamics. Several studies have pointed out some commensurabilities, sometimes using the fast Fourier transform technique. We intend to precisely identify the commensurabilities between the Pluto-Charon satellites, using the tool of fine frequency analysis, not only to investigate known commensurabilities but also to explore new ones. We used a combination of analytical and numerical approaches. The epicyclic theory of Lee and Peale served as an initial description of the motions and a comparative benchmark for numerical integrations. These integrations were performed using the IAS15 integrator within the N-body orbital integrator, REBOUND, considering both 3-body with the central binary and a single moon, and complete 6-body models. Additionally, we applied Frequency Map Analysis to determine precisely the numerical values of the system's fundamental frequencies. Our fine frequency analysis successfully identified all fundamental frequencies of the system, along with a detailed examination of the associated uncertainties. The findings, obtained with both 3-body and 6-body numerical models, align well with predictions from the epicyclic analytical theory. Notably, we highlight commensurabilities previously reported and introduce novel ones. Furthermore, we demonstrate how smooth alterations of the initial conditions can lead to the observation of libration in specific arguments, providing insights into the dynamical behavior of such a complex system.