Orbital evolution of outer Solar System satellites

Grant #: NNX11AM48G
Senior Scientist: Matija Cuk

This proposal focuses on the dynamics of satellites orbiting three outer Solar System objects: Jupiter, Saturn and the dwarf planet Haumea. The proposed work is divided into three main themes, each dealing with one of the above systems. In each case we use dynamical models to uncover the past of the system. 

First, we propose to numerically integrate past tidal evolution of the Haumea's two satellites, in order to test the hypothesis of Ragozzine and Brown(2009) that their inclinations and eccentricities originated in a resonance (Task 1). Our model of the dynamics of resonance capture and escape will utilize imperfectly known parameters such as the average oblateness of Haumea, masses of the satellites and pre-resonance eccentricities and inclinations. Our simulation results will then be used to constrain these unknown parameters. Haumea's satellites offer us a unique example of the large scale tidal evolution of two large moons around a solid planet-sized object. 

Second, we will study how eccentric the orbit of Titan could have been in the past. Despite being circularized by satellite tides, Titan currently has an eccentricity of 0.03, indicating a puzzlingly high past eccentricity. We will use past interactions with other satellites to determine the largest allowable eccentricity that would still preserve the stability of the Saturnian regular satellite system (Task 2.1). An upper limit on Titan's past eccentricity helps put significant constraints on Titan's tidal response, and therefore on the character and the longevity of any possible oceans. We will also explore whether Titan could have obtained its eccentricity through ongoing chaotic interactions with Iapetus and the giant planets (Task 2.2). The similarity between the 900-year period of the Great Inequality of Jupiter and Saturn and a number of secular periods of Titan and Iapetus is likely to result in dynamical chaos, which may be producing otherwise unexplained inclination of Iapetus and eccentricity of Titan. 

Third, we will explore the ways in which the retrograde group of Jupiter's irregular satellites could have been captured. Some of these satellites are in a secular resonance with Jupiter, which suggests a past orbital migration, and may indicate a gas-drag capture. We will test whether the resonance capture could have lead to the survival of temporary satellites that were spiralling into proto-Jupiter due to gas drag (Task 3.1). We will also study whether a single encounter between Jupiter and a smaller protoplanet could have preferentially populated the orbital region of the present retrograde satellites, with some resonances forming later due to planetary migration (Task 3.2). Irregular satellite systems (and especially that of Jupiter) are sensitive records of the giant planet formation and migration, and we will use our results to constrain the early history of the Solar System. 

The proposed research is fundamental to the understanding of the origin and evolution of planetary satellites and Kuiper belt objects. The NRA for the OPR program states that `The Outer Planets Research (OPR) program supports diverse scientific investigations that contribute to the understanding of the giant planets in the outer Solar System, as well as the smaller solid bodies including comets, asteroids, and the Kuiper Belt'. The OPR objectives include `Improving our understanding of the evolution of the outer Solar System, including the giant planets, their satellites, and other small bodies.' Here we propose to study: 1) past evolution of the satellites of Haumea, 2) past orbital evolution of Titan and Iapetus, and 3) capture and evolution of retrograde satellites of Jupiter. Our goal is to constrain planetary formation processes and the events that have taken place in the Solar System over its history.