Regarding the Putative Eccentricity of Charon's Orbit

Abstract

Based on astrometry from an orbit derived by Hubble Space Telescope imagery, Charon's orbital eccentricity has been reported to be in the range of 0.003-0.008. Solar and planetary tides are orders of magnitude too small to induce the reported eccentricity. This nonzero value, if correct, therefore indicates some significant forcing against the two-body tidal equilibrium value, which should formally be zero. Here we follow up on a preliminary study to investigate whether the reported eccentricity of Charon's orbit could be due to gravitational perturbations by Kuiper belt object (KBO) flybys through the Pluto-Charon system and KBO impacts directly onto Pluto and Charon. We find it is unlikely that Charon's reported eccentricity could be caused by this effect. Although we cannot rule out some additional source of eccentricity excitation (e.g., an undiscovered satellite in the system, or a Kozai resonance), our analysis indicates it is plausible that Charon's actual orbital eccentricity is substantially smaller than the 0.003 lower limit reported previously.

Lévy Flights of Binary Orbits Due to Impulsive Encounters

“…However, our analysis alleviates their need for numerical simulations and predicts the entire distribution of the eccentricity. The distributions measured by Stern et al (2003) are not all correct as their model includes only impact parameters out to twice the semimajor axis. In their simulations where q = 3.5 and 4.0, this excludes the impacts that are most relevant over an eccentricity damping timescale.…”

Kozai Cycles, Tidal Friction, and the Dynamical Evolution of Binary Minor Planets

“…In addition, the Kozai mechanism may still excite small eccentricities in BMPs in the KCTF regime. Such excitations could be the source of small but nonzero eccentricities of BMPs in the KCTF regime, such as observed for the binary asteroid Emma and the Pluto-Charon system in the Kuiper Belt (Stern et al 2003;Marchis et al 2008). Such excitations are likely to be higher for BMPs with low-mass ratios.…”

Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL 61

“…The 0.05 eccentricity of the system thus appears difficult to explain from orbital evolution alone. Stern et al (2003) considered perturbations from surrounding bodies as a method to excite the putative eccentricity of the Pluto-Charon system. Scaling their detailed calculations to the circumstances of 2003 EL 61 , we find that typical eccentricities for the 2003 EL 61 system should be on the order of e ≈ 0.003, much smaller than the observed eccentricity.…”