Orbital analysis of the Pluto-Charon moon system’s mutual interactions and forced frequencies

Department of Physics, University of Patras, Patras, 26504 Rio, Greece
e-mail: dgakis@upnet.gr; kngourg@upatras.gr

Received: 9 August 2022
Accepted: 4 January 2023

Abstract

Context. The orbits of the four small moons in the Pluto-Charon system, Styx, Nix, Kerberos, and Hydra, are circumbinary, as Pluto and Charon form a binary dwarf planet. Consequently, the orbit of each moon is characterized by a number of frequencies, arising from the central binary and the mutual gravitational interactions.

Aims. In this work, we identify the most prominent of these forced frequencies using fast Fourier transforms.

Methods. Two methods were implemented, a semi-analytic and a numerical one, and comparisons are made.

Results. The results indicate that as a first approximation, moon orbits may well be modeled as the superposition of a series of inevitable oscillations induced by Pluto and Charon, deviating from circular orbits, even if the eccentricity is set to zero. Moreover, the mutual gravitational effects are significant in their long-term evolution, especially for the lighter moons Styx and Kerberos, activating modes that dominate the low-frequency region of the power spectrum. This becomes evident through the comparison of simulations where only one moon is included along with the binary dwarf planet and simulations of the entire six-body system. These modes become noticeable over long integration times and may affect the orbits of the lighter moons of the system.