Unveiled density wave in Saturn’s rings

This paper considers resonantly forced spiral density waves in a dense planetary ring that is close to the threshold for viscous overstability. We solved numerically the hydrodynamical equations for a dense thin disk in the vicinity of an inner Lindblad resonance with a perturbing satellite. Our numerical scheme is one-dimensional so that the spiral shape of a density wave is taken into account through a suitable approximation of the advective terms arising from the fluid orbital motion. This paper is a first attempt to model the co-existence of resonantly forced density waves and short-scale free overstable wavetrains as observed in Saturn’s rings, by conducting large-scale hydrodynamical integrations. These integrations reveal that the two wave types undergo complex interactions, not taken into account in existing models for the damping of density waves. In particular we found that, depending on the relative magnitude of both wave types, the presence of viscous overstability can lead to the damping of an unstable density wave and vice versa. The damping of the short-scale viscous overstability by a density wave was investigated further by employing a simplified model of an axisymmetric ring perturbed by a nearby Lindblad resonance. A linear hydrodynamic stability analysis as well as local N-body simulations of this model system were performed and support the results of our large-scale hydrodynamical integrations.

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Structure and dynamics of Saturn's rings as seen by the Voyager stellar occultation

International Astronomical Union Colloquium ◽

10.1017/s0252921100101228 ◽

1984 ◽

Vol 75 ◽

pp. 229-250

Author(s):

L.W. Esposito

Keyword(s):

Mass Density ◽

Density Wave ◽

Power Spectra ◽

Current Data ◽

Density Waves ◽

Stellar Occultation ◽

Dominant Individual ◽

Saturn’S Rings ◽

Detailed Search ◽

Saturn's Rings

The stellar occultation of δ Scorpii by Saturn's rings shows radial structure in Saturn's rings down to the resolution element of ~100m. Density waves, embedded moonlets, and other proposed mechanisms are insufficient to explain the observed structure. A limit of less than 100 density waves are likely to be found in the rings in the current data. Unresolved waves do not seem to play a major role, either. A detailed search and histogram of optical depth in the outer B ring show no evidence of embedded moonlets. The mass of Saturn's rings is 5(±3) x 10-8of Saturn's mass. Power spectra of the rings show no dominant individual wavelengths: we do not see any preferred size for radical structure in the rings. A straightforward comparison of earth-based photometry and the viscosity and mass density of the rings inferred from density wave observations leads to a model of the rings that is many-particles thick. The vertical thickness of the rings would be about 50 m.

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Comments on collision mechanics in ring systems

International Astronomical Union Colloquium ◽

10.1017/s0252921100101472 ◽

1984 ◽

Vol 75 ◽

pp. 407-422

Author(s):

William K. Hartmann

Keyword(s):

Asteroid Belt ◽

Surface Erosion ◽

Surface Layers ◽

Ring Systems ◽

Eclipse Observations ◽

Saturn’S Rings ◽

Saturn's Rings

ABSTRACTThe nature of collisions within ring systems is reviewed with emphasis on Saturn's rings. The particles may have coherent icy cores and less coherent granular or frosty surface layers, consistent with thermal eclipse observations. Present-day collisions of such ring particles do not cause catastrophic fragmentation of the particles, although some minor surface erosion and reaccretion is possible. Evolution by collisional fragmentation is thus not as important as in the asteroid belt.

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Voyager UVS observations of stellar occultations by the rings of Saturn

International Astronomical Union Colloquium ◽

10.1017/s0252921100101265 ◽

1984 ◽

Vol 75 ◽

pp. 265-277

Author(s):

J.B. Holbelg ◽

W.T. Forrester

Keyword(s):

Optical Depth ◽

Distance Scale ◽

Density Waves ◽

Ring Density ◽

Stellar Occultations ◽

Saturn’S Rings ◽

Saturn's Rings

ABSTRACTDuring the Voyager 1 and 2 Saturn encounters the ultraviolet spectrometers observed three separate stellar occultations by Saturn's rings. Together these three observations, which sampled the optical depth of the rings at resolutions from 3 to 6 km. can be used to establish a highly accurate distance scale allowing the identification of numerous ring features associated with resonances due to exterior satellites. Three separate observations of an eccentric ringlet near the location of the Titan apsidal resonance are discussed along with other ringlet-resonance associations occurring in the C ring. Density waves occurring in the A and B rings are reviewed and a detailed discussion of the analysis of one of these features is presented.

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