Dr. Ignacio Mosqueira

December 21, 2006

“Formation and Dynamics of Planetary Ring/Moon Systems”

NCC 2–1398

In this research the dynamics of the narrow Uranian rings have been studied, the formation of satellite systems of the giant planets have been investigated, and the likely connections existing between rings and moons concerning ring morphology and composition are being pursued. An investigation of three scenarios for ring particle collisions to alter the uniform precession condition applicable to rings that exhibit apse-alignment, bring the theory into better agreement with observations.AS model was generated for the formation, migration and survival of regular satellites of Jupiter, Saturn and Uranus in extended gaseous nebulae. Applications are noted principally to Callisto, Ganymede, Titan, Hyperion, Iapetus and the inner icy satellites of Saturn, are predictions testable by Cassini have been made.An explanation for the Ganymede-Callisto dichotomy is presented that does not rely on fine-tuning poorly known parameters. The research will improve existing ring models by generalizing the streamline precession term due to particle collisions to cases such that the density gradients in the ring take place over lengthscales comparable to the mean free path of a ring particle, and to include the effects of shepherd satellites in the determination of ring masses. A study will be made of the structure of the outer B ring. The satellite formation model will be extended to Neptune by considering a scenario in which Neptune’s primordial satellite system was largely analogous to that of Uranus, so as to determine whether the capture of Triton from heliocentric orbits is consistent with the present semi-major axis, eccentricity and inclination of Nereid. We will explore the connections between our satellite formation model, the resulting properties of the inner moons of the giant planets, and the consequences to their ring systems—in particular, (a) why Jupiter has a less massive ring system than Saturn, and (b), why Saturn’s rings have high albedo and appear to be made mostly of water ice, while no spectral evidence for the presence of water ice has been found in the case of the Uranian rings. A study will be made of the thermal histories of Ganymede, Callisto and Titan and we will investigate the predictions that current satellite formation models make for the state of Titan when compared to those of Ganymede and Callisto. This research will also adapt a symplectic code to efficiently handle the bombardment of accreting satellite embryos by heliocentric planetesimals in order to address the issue of why Titan is the only large Saturnian satellite. We are expanding our satellite formation model to include 3-D effects on our tidal torque calculations, and are investigating the disk conditions that led to the primordial capture of Hyperion into a 4:3 resonance with Titan but failed to either to capture or to retain such objects in the case of Ganymede and Callisto. By expanding our knowledge base in several key areas as of 2004, the upcoming Cassini mission makes these exciting and timely areas of research.