An Evolving View of Saturn’s Dynamic Rings

Cuzzi, J. N.; Burns, Joseph A.; Charnoz, Sébastien; Clark, R. N.; Colwell, J. E.; Dones, L.; Esposito, L. W.; Filacchione, G.; French, R. G.; Hedman, M. M.; Kempf, S.; Marouf, E. A.; Murray, C. D.; Nicholson, P.; Porco, C. C.; Schmidt, J.; Showalter, M. R.; Spilker, L. J.; Spitale, J. N.; Srama, R.; Sremčević, M.; Tiscareno, Matthew S.; Weiss, J. W.

doi:10.1126/science.1179118

Cited by 130 publications

(89 citation statements)

References 62 publications

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“…B ombardment of Saturn's rings by interplanetary meteoroids (1)(2)(3) and the observation of rapid processes in the ring system (4) indicate that the shape of the particle size distribution is likely not primordial or a direct result of the ring-creating event. Rather, ring particles are believed to be involved in active accretion-destruction dynamics (5-13) and their sizes vary over a few orders of magnitude as a power law (14)(15)(16)(17), with a sharp cutoff for large sizes (18)(19)(20)(21).…”

mentioning

confidence: 99%

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

Brilliantov

Krapivsky

Bodrova

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

135

129

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Saturn's rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, ∼ r −q with q ≈ 3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75 ≤ q ≤ 3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn's rings. (1-3) and the observation of rapid processes in the ring system (4) indicate that the shape of the particle size distribution is likely not primordial or a direct result of the ring-creating event. Rather, ring particles are believed to be involved in active accretion-destruction dynamics (5-13) and their sizes vary over a few orders of magnitude as a power law (14-17), with a sharp cutoff for large sizes (18-21). Moreover, tidal forces fail to explain the abrupt decay of the size distribution for house-sized particles (22). One wishes to understand the following: (i) Can the interplay between aggregation and fragmentation lead to the observed size distribution? And (ii) is this distribution peculiar for Saturn's rings, or is it universal for planetary rings in general? To answer these questions quantitatively, one needs to elaborate a detailed model of the kinetic processes in which the ring particles are involved. Here we develop a theory that quantitatively explains the observed properties of the particle size distribution and show that these properties are generic for a steady state, when a balance between aggregation and fragmentation holds. Our model is based on the hypothesis that collisions are binary and that they may be classified as aggregative, restitutive, or disruptive (including collisions with erosion); which type of collision is realized depends on the relative speed of colliding particles and their masses. We apply the kinetic theory of granular gases (23, 24) for the multicomponent system of ring particles to quantify the collision rate and the type of collision. Results and DiscussionModel. Ring particles may be treated as aggregates built up of primary grains (9) of a certain size r 1 and mass m 1 . [Observations indicate that particles below a certain radius are absent in dense rings (16).] Denote by m k = km 1 the mass of rin...

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mentioning

confidence: 99%

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

Brilliantov

Krapivsky

Bodrova

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

135

129

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“…Our understanding of these mechanisms is highly relevant to other disc systems, including protoplanetary and debris discs. Existing data give preliminary hints that self-gravity wakes and spiral density waves, which are important diagnostics as well as driving phenomena in Saturn's rings (e.g., Cuzzi et al, 2010), also exist in at least some parts of Uranus' rings, but much more detailed observation is needed to characterise them.…”

Section: How Do Dense Rings Behave Dynamically?mentioning

confidence: 99%

The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets

Arridge¹,

Achilleos²,

Agarwal³

et al. 2014

Planetary and Space Science

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“…It is difficult to estimate the mass of a ring system without an orbiting spacecraft, so reliable estimates of the mass of the rings have come about only recently, based on Cassini observations. Much of the mass is concentrated in the A and B rings, which together contain about 10 22 to 10 23 grams of icy material [115,116]. If all of the ring material were gathered into a single object, it would correspond to an icy satellite 150 to 300 km in radius, roughly the size of Saturn's moon Mimas.…”

Section: Ringsmentioning

confidence: 99%

Formation of exomoons: a solar system perspective

Barr

2016

Astronomical Review

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Satellite formation is a natural by-product of planet formation. With the discovery of numerous extrasolar planets, it is likely that moons of extrasolar planets (exomoons) will soon be discovered. Some of the most promising techniques can yield both the mass and radius of the moon. Here, I review recent ideas about the formation of moons in our Solar System, and discuss the prospects of extrapolating these theories to predict the sizes of moons that may be discovered around extrasolar planets. It seems likely that planet-planet collisions could create satellites around rocky or icy planets which are large enough to be detected by currently available techniques. Detectable exomoons around gas giants may be able to form by co-accretion or capture, but determining the upper limit on likely moon masses at gas giant planets requires more detailed, modern simulations of these processes.

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An Evolving View of Saturn’s Dynamic Rings

Cited by 130 publications

References 62 publications

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets

Formation of exomoons: a solar system perspective

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