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| Titel |
Fine-Scale ~ 100 m Density Wave Structure of the Saturnian Ring Disk: A Hydrodynamic Theory |
| VerfasserIn |
E. Griv, M. Gedalin |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022256
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| Zusammenfassung |
| The linear stability of the Saturnian ring disk of mutually gravitating and physically colliding
particles is examined with special emphasis on its fine-scale of the order of 100 m or even
less density wave structure (almost regularly spaced, aligned cylindric density enhancements
and optically-thin zones with the width and the spacing between them of roughly
several tens particle diameters). Jeans instabilities of gravity perturbations (e.g.,
those produced by a spontaneous disturbance) are analyzed analytically through
the use of Navier-Stokes equations of a compressible fluid. An essential feature
of this study is that the theory is not restricted by any assumptions regarding the
thickness of the system. The simple model of the system is considered: the ring
disk is considered to be thin and its structure is considered in a horizontally local
Wenzel-Kramer-Brillouin (or short-wavelength) approximation. A plasma physics
method is given for the solution of the self-consistent system of the gasdynamical
equations and the Poisson equation describing the stability of Saturn’s A, B, and C
rings when the system is perturbed in an arbitrary manner. That is, when a gravity
perturbation does not distort the rings’ plane (modes of even symmetry with respect to
the equatorial plane, or even Jeans-type perturbations) and when does distort the
rings’ plane (odd bending-type perturbations). This approach is introduced here
for the first time in an astrophysical context. We show that the disk is probably
unstable and gravity perturbations grow effectively within a few orbital periods;
self-gravitation plays a key role in the formation of the fine-scale structure while
particle collisions play a secondary role. It appears very likely that some of the
microstructures in Saturn’s rings recently revealed by the CASSINI spacecraft high-resolution
observations is a manifestation of these density wave effects. The predictions of
the theory are compared with observations of Saturn’s rings by the CASSINI and
are found to be in good agreement. Particulary, we show that the quasi-periodic
density enhancements are flattened structures, with height/width ratio of about
0.3.
This work was supported in part by the Israel Science Foundation and the Binational
US-Israel Science Foundation. |
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