The Evolution of Rings and Satellites

Andrew J Hesselbrock, Purdue University

Abstract

Planetary rings are, and have been, a common feature throughout the solar system. Rings have been observed orbiting each of the giant planets, several Trans-Neptunian Objects, and debris rings are thought to have orbited both Earth and Mars. The bright, massive planetary rings orbiting Saturn have been observed for centuries, and the Cassini Mission has given researchers a recent and extensive closeup view of these rings. The Saturn ring system has served as a natural laboratory for scientists to understand the dynamics of planetary ring systems, as well as their influence on satellites orbiting nearby. Researchers have shown that planetary ring systems and nearby satellites can be tightly-coupled systems.In this work, I discuss the physics which dominate the dynamical evolution of planetary ring systems, as well as the interactions with any nearby satellites. Many of these dynamics have been incorporated into a one-dimensional mixed Eulerian-Lagrangian numerical model that I call “RING-MOONS,” to simulate the long-term evolution of tightly coupled satellite-ring systems. In developing RING-MOONS, I have discovered that there are three evolution regimes for tightly-coupled satellite-ring systems which I designate as the “Boomerang,” “Torque-Dependent,” and “Slingshot” regimes. Each regime may be defined using the rotation period of the primary body and the bulk density of the ring material.The slow rotation period of Mars places it in the Boomerang regime. I hypothesize that a giant impact with Mars ejected material into orbit, forming a debris ring around the planet. Using RING-MOONS, I demonstrate how Lindblad torques cause satellites which form at the edge of the ring to initially migrate away from the ring, but over time as the mass of the ring decreases, tidal torques always cause the satellites to migrate inwards. Assuming the satellites rapidly tidally disrupt upon migrating to the rigid Roche limit, a new ring is formed. I show that debris material cycles between orbiting Mars as a planetary ring, or as discrete satellites, and that Phobos may be a product of a repeated satellite-ring cycle. Uranus, which has a faster rotation rate falls within the Torque-Dependent regime. Hypothesizing that a massive ring once orbited Uranus, I use RING-MOONS to demonstrate how the satellite Miranda may have formed from such a ring, and migrated outwards to its current orbit, but that any other satellites would have migrated inwards overtime.Lastly, I examine Trans-Neptunian Objects (TNOs) in binary systems. Tidal torques exerted on each body can decrease the mutual semi-major axis of the system. I outline the conditions for which a fully synchronous system may experience a complete decay of the mutual orbit due to tidal torques. As the semi-major axis decreases, it is possible for the smaller of the two bodies to shed mass before coming into contact with the more massive to form a contact binary. I hypothesize that Chariklo and Chiron are contact binaries that formed via the tidal collapse of a binary TNOs system, and demonstrate how mass shedding may have occurred to form the rings observed today.

Degree

Ph.D.

Advisors

Minton, Purdue University.

Subject Area

Astronomy|Mathematics

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