Microwave observations of Saturn's rings: anisotropy in directly transmitted and scattered saturnian thermal emission

Dunn, D. E.; Molnar, Lawrence A.; Niehof, Jon; Pater, Imke de; Lissauer, Jack J.

doi:10.1016/j.icarus.2004.04.008

Cited by 29 publications

(13 citation statements)

References 23 publications

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“…In Saturn's rings, the preferred orientation of excited gravitationally unstable density waves produces brightness azimuthal variations similar to those observed by Camichel (1958), Lumme & Irvine (1976), Lumme et al (1977), Thompson et al (1981), Franklin et al (1987), Dones et al (1993), Dunn et al (2004), French et al (2007), and others. Even though the analysis presented here shows that there is a dominant nonaxisymmetric (ψ 0) Fourier mode of maximum instability with λ crit ≈ 100 m, at the present time we cannot explain the angle ψ crit in the local WKB version of our theory.…”

Section: Discussionsupporting

confidence: 79%

“…As for the present study, the Jeans-unstable spiral density waves also cause the ring A's quadrupole azimuthal brightness asymmetry detected first by Camichel (1958) and then by Lumme & Irvine (1976), Lumme et al (1977), Thompson et al (1981), Franklin et al (1987), Dones et al (1993), Dunn et al (2004), and others (see , for a discussion). The physics underlying these selfgravity waves is essentially the same as the "density wave structure" which was studied in the context of galactic disks by Lin & Shu (1966), Lin et al (1969), Shu (1970), Lau & Bertin (1978), Lin & Lau (1979), Bertin (1980), Morozov (1980), Montenegro et al (1999), Griv et al (2002), and others.…”

Section: Fine-scale Structuresupporting

confidence: 78%

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Fine-scale density wave structure of Saturn's rings: A hydrodynamic theory

Griv

Gedalin

2010

A&A

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Aims. We examine the linear stability of the Saturnian ring disk of mutually gravitating and physically colliding particles with special emphasis on its fine-scale ∼100 m density wave structure, that is, 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. Methods. We analyze the Jeans' instabilities of gravity perturbations (e.g., those produced by a spontaneous disturbance) analytically by using the Navier-Stokes dynamical equations of a compressible fluid. The theory is not restricted by any assumptions about the thickness of the system. We consider a simple model of the system consisting of a three-dimensional ring disk that is weakly inhomogeneous and whose structure is analyzed by making a horizontally local short-wave approximation. Results. We demonstrate that the disk is probably unstable and that gravity perturbations grow effectively within a few orbital periods. We find that self-gravitation plays a key role in the formation of the fine structure. The predictions of the theory are compared with observations of Saturn's rings by the Cassini spacecraft and are found to be in good agreement. In particular, it appears very likely that some of the quasi-periodic microstructures observed in Saturn's A and B rings -both axisymmetric and nonaxisymmetric onesare manifestations of these effects. We argue that the quasi-periodic density enhancements revealed in Cassini data are flattened structures, with a height to width ratio of about 0.3. One should analyze high-resolution of the order of 10 m data acquired for the A and B rings (and probably C ring as well) to confirm this prediction. We also show that the gravitational instability is a potential cluster-forming mechanism leading to the formation of porous 100-m-diameter moonlets of preferred mass ∼10 7 g each embedded in the outer A ring, although this has yet to be directly measured.

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Section: Discussionsupporting

confidence: 79%

Section: Fine-scale Structuresupporting

confidence: 78%

Fine-scale density wave structure of Saturn's rings: A hydrodynamic theory

Griv

Gedalin

2010

A&A

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“…Ground-based observations have suggested that the particle size distribution extends to smaller sizes in the trans-Encke region than it does anywhere else in the A ring ( French and Nicholson 20 0 0 ). Determining particle sizes in Saturn's rings is complicated by azimuthal brightness asymmetries found in Saturn's A and B rings ( Camichel, 1958;Colombo et al, 1976;Lumme and Irvine, 1976;Reitsema et al, 1976;Lumme et al, 1977;Gehrels and Esposito, 1981;Thompson et al, 1981;Dones and Porco, 1989;Dones et al, 1993;Dunn et al, 2004;Nicholson et al, 2005 ). These observations have since been explained by the presence of aligned trailing density enhancements ( Julian and Toomre 1966 ) now known as selfgravity wakes ( Colwell et al 2006 ).…”

Section: Introductionmentioning

confidence: 99%

Small particles and self-gravity wakes in Saturn's rings from UVIS and VIMS stellar occultations

Jerousek

Colwell

Esposito

et al. 2016

Icarus

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“…For a more realistic illustration, see Fig. 3. radiation transmitted through the rings (Dunn et al, 2004). Wake structure has also been suggested to explain the asymmetry in the thermal radiation scattered by the rings (van der Tak et al, 1999;Dunn et al, 2002); due to Saturn being the source of radiation this asymmetry manifests as a difference between East and West ansae (not to be confused with the visual 'east-west asymmetry' mentioned above).…”

Section: Introductionmentioning

confidence: 99%