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

TL;DR

This study analyzes the mutual gravitational interactions and forced frequencies in the Pluto-Charon moon system, revealing that the moons' orbits can be modeled as superpositions of oscillations induced by the binary and mutual effects, especially affecting lighter moons over time.

Contribution

It introduces a combined semi-analytic and numerical approach to identify dominant forced frequencies in the Pluto-Charon system, highlighting the significance of mutual gravitational effects on moon orbits.

Findings

Orbits can be approximated as superpositions of forced oscillations.

Mutual gravitational effects significantly influence long-term orbital evolution.

Lighter moons are more affected by these modes over extended periods.

Abstract

Context. The orbits of the four small moons in the Pluto-Charon system, Styx, Nix, Kerberos and Hydra, are circumbinary, as the former form a binary dwarf planet. Consequently, the orbit of each one of them is characterized by a number of frequencies, arising by the central binary and the mutual gravitational interactions. Aims. In this work, we identify the most prominent of these forced frequencies using Fast Fourier Transformations. Methods. Two methods are implemented, a semi-analytic and a numerical one, and comparisons are being made. Results. The results indicate that as a first approximation, moon orbits may well be modelled as the superposition of a series of inevitable oscillations, induced by Pluto and Charon, deviating from circular ones, 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.