On the existence of regular and irregular outer moons orbiting the Pluto-Charon system

TL;DR

This study investigates how the Sun's gravitational effects influence the orbits of potential outer moons and rings around Pluto, suggesting that irregular, highly inclined satellites are more likely to exist beyond a certain distance due to secular evolution.

Contribution

It demonstrates that solar perturbations significantly affect outer satellite orbits around Pluto, predicting the existence of irregular, inclined moons beyond the inner system.

Findings

Secular evolution affects outer satellites beyond 0.0035 AU.

Outer satellites likely to be irregular and highly inclined.

Potential for detection by New Horizons mission.

Abstract

The dwarf planet Pluto is known to host an extended system of five co-planar satellites. Previous studies have explored the formation and evolution of the system in isolation, neglecting perturbative effects by the Sun. Here we show that secular evolution due to the Sun can strongly affect the evolution of outer satellites and rings in the system, if such exist. Although precession due to extended gravitational potential from the inner Pluto-Charon binary quench such secular evolution up to $a_{crit}\sim0.0035$ AU ($\sim0.09$ $R_{Hill}$ the Hill radius; including all of the currently known satellites), outer orbits can be significantly altered. In particular, we find that \emph{co-planar} rings and satellites should not exist beyond $a_{crit}$; rather, satellites and dust particles in these regions secularly evolve on timescales ranging between $10^{4}-10^{6}$ yrs, and quasi-periodically change their inclinations and eccentricities through secular evolution (Lidov-Kozai oscillations). Such oscillations can lead to high inclinations and eccentricities, constraining the range where such satellites (and dust particles) can exist without crossing the orbits of the inner satellites, or crossing the outer Hill stability range. Outer satellites, if such exist are therefore likely to be \emph{irregular} satellites, with orbits limited to be non-circular and/or highly inclined. These could be potentially detected and probed by the New-Horizon mission, possibly providing direct evidence for the secular evolution of the Pluto satellite system, and shedding new light on its origins.