Self-gravity wakes and radial structure of Saturn's B ring

Colwell, Joshua; Esposito, L. W.; Sremčević, M.; Stewart, G. R.; McClintock, W. E.

doi:10.1016/j.icarus.2007.03.018

Cited by 116 publications

(138 citation statements)

References 32 publications

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“…Radial wavelike axisymmetric structures with a wavelength of 100 -200 m have indeed been found independently in UVIS and RSS occultation scans of Cassini [19,74], proving the existence of overstability in the rings.…”

Section: Viscous Overstabilitymentioning

confidence: 70%

Hydrodynamics of Saturn’s Dense Rings

Seiß

Spahn

2011

Math. Model. Nat. Phenom.

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Abstract. The space missions Voyager and Cassini together with earthbound observations revealed a wealth of structures in Saturn's rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn's moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Furthermore, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn's dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves.

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Section: Viscous Overstabilitymentioning

confidence: 70%

Hydrodynamics of Saturn’s Dense Rings

Seiß

Spahn

2011

Math. Model. Nat. Phenom.

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“…The ragged, "irregular" structure formation process in planetary rings was demonstrated in the simulations carried out by Salo (1992Salo ( , 1995 and others (e.g., Griv 2005a;Griv & Gedalin 2005) and observed in Cassini experiments (e.g., Colwell et al 2007, p. 142, "the sheets are loosely organized into the trailing spiral density enhancements"). Cassini observations indicated that axisymmetric periodic microstructure in Saturn's rings coexists with nonaxisymmetric structure (Colwell 2006(Colwell , 2007Thomson et al 2007). Clearly, in this case of both radial and spiral excitation, the distribution of the surface density along the spiral arms is not uniform, but describes a sequence of maxima, that might be identified with forming embedded clusters of particles, resembling a "beads on a string" structure.…”

Section: Formation Of Clumpsmentioning

confidence: 99%

“…5A and F therein), and then Cassini UVIS and radio occultations (Colwell et al 2006(Colwell et al , 2007Thomson et al 2007). Cassini VIMS observations ) and infrared observations of Saturn's rings by Cassini CIRS (Leyrat et al 2008a;Ferrari et al 2009) also detected fine structure in the A ring.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Typical collision velocities in the unperturbed rings are well below 1 cm s −1 (Esposito 2002;Colwell et al 2009), but gravitational perturbations may raise the average collision speed considerably. The collisions dissipate kinetic energy from the rings and thereby determine the stability of the rings Schmidt et al 2001); consequently, data pertaining to collisional properties and outcomes are vital to model efforts which are used to understand ring instabilities, wakes and overall structure, including the very strongly confined heights observed in Saturnian and other ring systems (Colwell et al 2006(Colwell et al , 2007Hedman et al 2007;Thomson et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Collisions of small ice particles under microgravity conditions

Hill

Heißelmann

Blum

et al. 2015

A&A

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Context. Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims. Collisions of 1.5 cm ice spheres composed of pure crystalline water ice, water with 5% methanol, and water with 5% formic acid were investigated to determine the effect of the ice composition on the collisional outcomes. Methods. The collisions were conducted in a dedicated experimental instrument, operated under microgravity conditions, at relative particle impact velocities between 0.01 and 0.19 m s −1 , temperatures between 131 and 160 K and a pressure of around 10 −5 mbar. Results. A range of coefficients of restitution were found, with no correlation between this and the chemical composition, relative impact velocity, or temperature. Conclusions. We conclude that the chemical composition of the ice (at the level of 95% water ice and 5% methanol or formic acid) does not affect the collisional properties at these temperatures and pressures due to the inability of surface wetting to take place. At a level of 5% methanol or formic acid, the structure is likely to be dominated by crystalline water ice, leading to no change in collisional properties. The surface roughness of the particles is the dominant factor in explaining the range of coefficients of restitution.

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Self-gravity wakes and radial structure of Saturn's B ring

Cited by 116 publications

References 32 publications

Hydrodynamics of Saturn’s Dense Rings

Hydrodynamics of Saturn’s Dense Rings

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

Collisions of small ice particles under microgravity conditions

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