The Composition of Saturn's Rings

Poulet, F.; Cuzzi, J. N.

doi:10.1006/icar.2002.6967

Cited by 48 publications

(27 citation statements)

References 34 publications

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“…A hint of an impurity band near 0.85 µm was reported by Clark (1980). Recently, the composition of the rings has been studied by modeling a composite spectrum (0.3-4.0 µm) of the overall main rings with a Shkuratov-type albedo model by Poulet & Cuzzi (2002). This study confirmed that the reddish absorber likely is represented by tholins which are molecularly mixed with water ice particles.…”

Section: Introductionmentioning

confidence: 53%

Compositions of Saturn's rings A, B, and C from high resolution near-infrared spectroscopic observations

Poulet

Cruikshank

Cuzzi

et al. 2003

A&A

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Abstract. We used the NASA IRTF spectrograph SpeX to obtain near-infrared spectra (0.9-5.4 µm) of Saturn's rings, achieving spectral resolution λ/∆λ of about 2000. The spatial resolution (about 1 arcsec) is sufficient to distinguish the three main ring components (A, B and C rings) from one another. These new observations of Saturn's rings are the first to combine an extended spectral range with high spectral resolution and good spatial resolution. We combined these data with recent photometric observations acquired by HST in the 0.3-1.0 µm range. The spectra of the A band B rings are dominated by strong features due to crystalline water ice. The shape and the depth of these absorptions differ for each ring, which indicates different water ice grain sizes and abundances. No spectral evidence for volatile ices other than water ice has been detected. Both the lower albedo and the less blue slope in the near-infrared reflectance of the C ring indicate a concentration of dark material different from that in the A and B rings. The broader triangular Fresnel reflection peak at 3.1 µm may support the presence of some amount of amorphous ice. The C ring spectrum exhibits bands centered at 1.73 and 3.4 µm which agree in position quite well with the C-H bands. Although the detection is probable, it requires confirmation. With a radiative transfer model, we constrain the grain sizes and the relative abundances of water ice, a dark colorless component (amorphous carbon) to adjust the albedo and a second contaminant to reproduce the reddening in the UV-visible range represented here by organic tholins. The dark component of the C ring spectrum is included as an intra-mixture only. The cosmogenic implications of the inferred compositions are discussed.

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Section: Introductionmentioning

confidence: 53%

Compositions of Saturn's rings A, B, and C from high resolution near-infrared spectroscopic observations

Poulet

Cruikshank

Cuzzi

et al. 2003

A&A

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“…3) (16). Because the rings_ scattering function is insensitive to the physical thickness of the rings in this intermediate-phase viewing geometry, our spectra provide evidence that most small-scale variations in ring brightness result from compositional differences (17,18). If the rings began as nearly pure water ice, regions of smaller optical depth are expected to become more polluted by interplanetary dust, resulting in reduced particle albedos (19,20).…”

Section: S P E C I a L S E C T I O Nmentioning

confidence: 81%

Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites

Porco

Baker

Barbara

et al. 2005

Science

184

128

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Images acquired of Saturn's rings and small moons by the Cassini Imaging Science Subsystem (ISS) during the first 9 months of Cassini operations at Saturn have produced many new findings. These include new saturnian moons; refined orbits of new and previously known moons; narrow diffuse rings in the F-ring region and embedded in gaps within the main rings; exceptionally fine-scale ring structure in moderateâ to highâoptical depth regions; new estimates for the masses of ring-region moons, as well as ring particle properties in the Cassini division, derived from the analysis of linear density waves; ring particle albedos in select ring regions; and never-before-seen phenomena within the rings.

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“…In the optical, the ring particle albedo increases toward larger wavelengths becoming then flat enough up to ∼1.5 µm (e.g., Poulet & Cuzzi 2002;Porco et al 2005) so that α V is about the value in the green filter. The situation is much less known in the mid-infrared where Saturn's emissivity is maximum.…”

Section: Heat Diffusion Equation and Its Scalingmentioning

confidence: 99%

“…Measurements of optical parameters for polluted ices by Hudgins et al (1993) in the relevant temperature and spectral range reveal several absorption features. Generally, though the mid-infrared absorptivity α I is assumed to be close to unity for the inferred composition (e.g., Irvine & Pollack 1968;Kawata & Irvine 1975;Hudgins et al 1993;Poulet & Cuzzi 2002;Poulet et al 2003).…”

Section: Heat Diffusion Equation and Its Scalingmentioning

confidence: 99%

Thermal forces on planetary ring particles: application to the main system of Saturn

Vokrouhlický

Nesvorný

Dones

et al. 2007

A&A

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Context. The motion of small particles in planetary rings is affected in the long-term by radiation forces. While the PoyntingRobertson effect has been extensively discussed and applied to the dynamics of micron-sized ring particles, studies of thermal selfacceleration of particles are only in their infancy. Aims. We extend the pioneering work of Rubincam (2006, Icarus 184, 532) by a more thorough analytical formulation of both planetary and solar thermal forces on ring particles. Methods. Within a sparse disk model we analytically compute both seasonal and diurnal variants of the thermal forces and we demonstrate that the diurnal effect components vanish for a sample of rapidly rotating particles with randomly oriented spin axes. For sufficiently slowly rotating ring particles, though, these diurnal components might significantly modify the expected planetocentric secular drift rates of their orbits. We also take into account the orbital effects of Poynting-Robertson drag that begin to dominate the thermal forces for particles with sizes ≤5 mm. Our formulation of the Poynting-Robertson drag is the first to account properly for the influence of the planetary shadow. Results. We critically review the previous suggestion that Saturn's A and B ring boundaries might correlate with radiative null-torque orbits of small particles. Using the best estimates of optical and thermal parameters of Saturn's ring particles, we show that the millimetre to several centimetre size particles mostly drift inward to the planet with a characteristic radial speed ν r ∼ 3 × 10 −6 cm/s, corresponding to drift across the whole main ring system in ∼(1−5) × 10 8 years if the effects of inter-particle collisions are neglected. The radial speed is comparable to, or even larger than, the effective radial drift rate of small particles due to redistribution of collisional ejecta from micrometeoroid impacts. Therefore, radiation forces may be important for estimating the evolution timescales of Saturn's rings as derived from the ballistic transport theory. We propose that, in addition to collisional coagulation, radiation forces may efficiently remove centimetre-sized particles and thus help explain the observed paucity of these particles in Saturn's rings. A population of particles with spin axes aligned with normal to the disk plane, if it exists, would experience a net outward drift provided their rotation rate is larger than their orbital frequency.

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The Composition of Saturn's Rings

Cited by 48 publications

References 34 publications

Compositions of Saturn's rings A, B, and C from high resolution near-infrared spectroscopic observations

Compositions of Saturn's rings A, B, and C from high resolution near-infrared spectroscopic observations

Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites

Thermal forces on planetary ring particles: application to the main system of Saturn

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