Orbital Evolution of Outer Solar System Satellites

Grant #: NNX14AO38G
Senior Scientist: Matija Cuk

This proposal focuses on the dynamics of satellites orbiting three outer solar system objects: Saturn, Pluto and the triple trans-Neptunian object (TNO) 1999 TC_36. The proposed work is divided into two main themes, one dealing with the dynamical evolution of the Saturnian satellite system, and the other concentrating on the dynamics of gravitationally bound fragments in TNO collisions. 

First, we will test the recent suggestion by Lainey et al.(2012) that the tidal response of Saturn is an order of magnitude stronger than commonly thought. They claim that this stron ger tidal response is causing orbital migration of Saturn's moons that is faster than current estimates. Lainey et al.(2012) derive this fast migration from long-baseline astrometric data, and show that low tidal Q could explain the heat flux of Enceladus. Faster tidal evolution is also consistent with the evolved state of the Titan-Hyperion resonance, but implies a relatively recent (re)accretion of the icy moons interior to Titan. In Task 1.1, we propose to study a possible past resonance involving the Sun, Titan and previous-generation icy satellites (similar to Enceladus and Dione). For the fast tidal evolution to be viable, this resonance must be able to generate the present eccentricity of Titan and destabilize the previous generation of medium-sized satellites. In Task 1.2, we will revisit resonant encounters between the extant icy satellites as they evolved into their present orbits, and compare results acquired using low and high tidal Q values. In Task 1.3, we will explore the dynamics of Iapetus over billions of years. Iapetus is unique among satellites as it is equally perturbed by Titan and the Sun. We will construct a secular model to efficiently model Iapetus's orbit, and constrain possible changes to its initial eccentricity and inclination over the last 4 Gyr. 

Second, we will study the dynamics of eccentric debris originating in collisions that formed the Pluto-Charon binary and possibly the 1999 TC_36 triple. Both systems have large obliquities, enabling loosely bound ejecta from the collisions to experience strong perturbations from the Sun (the "Kozai resonance"). This process could decouple the debris from the inner boundary long enough for the inner binary to evolve tidally and prevent further Kozai oscillations. In Task 2, we will construct a full Bulirsch-Stoer integrator in order to determine if such material could eventually form the small moons of Pluto. We will apply the same analysis to the TNO triple 1999 TC_36}. We will also explore whether solar resonances affect the dynamics of the resultant proto-satellite disk around Pluto.