On the Origin of Pluto's Small Satellites by Resonant Transport

TL;DR

This paper investigates whether Pluto's small satellites could have been transported to their current orbits via mean-motion resonances during Pluto-Charon's tidal evolution, concluding it is highly unlikely.

Contribution

The study demonstrates that stable resonant transport of Pluto's small satellites during tidal evolution is improbable under realistic conditions.

Findings

Stable resonance capture is possible at 5:1, 6:1, and 7:1 commensurabilities.

Resonant transport at 3:1 and 4:1 is not stable.

Resonant transport is unlikely given the orbital eccentricities and Pluto's shape parameters.

Abstract

The orbits of Pluto's four small satellites (Styx, Nix, Kerberos, and Hydra) are nearly circular and coplanar with the orbit of the large satellite Charon, with orbital periods nearly in the ratios 3:1, 4:1, 5:1, and 6:1 with Charon's orbital period. These properties suggest that the small satellites were created during the same impact event that placed Charon in orbit and had been pushed to their current positions by being locked in mean-motion resonances with Charon as Charon's orbit was expanded by tidal interactions with Pluto. Using the Pluto-Charon tidal evolution models developed by Cheng et al. (2014), we show that stable capture and transport of a test particle in multiple resonances at the same mean-motion commensurability is possible at the 5:1, 6:1, and 7:1 commensurabilities, if Pluto's zonal harmonic $J_{2P} = 0$. However, the test particle has significant orbital eccentricity at the end of the tidal evolution of Pluto-Charon in almost all cases, and there are no stable captures and transports at the 3:1 and 4:1 commensurabilities. Furthermore, a non-zero hydrostatic value of $J_{2P}$ destroys the conditions necessary for multiple resonance migration. Simulations with finite but minimal masses of Nix and Hydra also fail to yield any survivors. We conclude that the placing of the small satellites at their current orbital positions by resonant transport is extremely unlikely.