Collisional Features in Saturn's F Ring.
Abstract
The role of physical collisions in shaping Saturn's F ring is explored using a mixture
of dynamical theory, image analysis and computer simulations. The F ring is highly
dynamic, being perturbed by the nearby moons, Prometheus and Pandora, and by
a population of small bodies, whose presence is inferred by their influence on the
ring, charged particle data and, occasionally, direct detection.
Small-scale features, termed `mini-jets', are catalogued from images taken by the
Imaging Science Subsystem of the Cassini spacecraft. More than 1000 are recorded,
implying a population of 100 objects on nearby orbits, colliding with the ring at
velocities of a few ms1. Many are seen to collide several times, forming repeated
structures, and must have enough physical strength, or self-gravity, to survive multiple
passages through the core.
Larger features, called `jets', share a similar morphology. They are likely caused
by a more distant population which collide at higher velocities ( 10 ms1) and
are roughly an order of magnitude less common. Differential orbital motion causes
jets to shear out over time, giving the ring its multi-stranded appearance. Jets have
different orbital properties to mini-jets, probably because they result from multiple,
overlapping collisions.
Simulations using an N-body code show that the shape of collisional features depends
heavily on the coefficient of restitution, particularly the tangential component.
When both components are < 1 large objects merely sweep up small particles. Features
like jets and mini-jets require large particles in both the target and impactor,
as is the case for two similarly-sized aggregates colliding.
A single population of aggregates is proposed, ranging from large, unconsolidated
clumps, embedded in the core, through mini-jet-forming objects to the more distant,
jet-forming colliders. Prometheus may be ultimately responsible for all of these
features as its gravity can trigger clump formation as well as perturb particles.
Authors
Attree, Nicholas OliverCollections
- Theses [3706]