The Christiansen Effect in Saturn's narrow dusty rings and the spectral identification of clumps in the F ring

Abstract

Stellar occultations by Saturn's rings observed with the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft reveal that dusty features such as the F ring and the ringlets in the Encke and the Laplace Gaps have distinctive infrared transmission spectra. These spectra show a narrow optical depth minimum at wavelengths around 2.87 microns. This minimum is likely due to the Christiansen Effect, a reduction in the extinction of small particles when their (complex) refractive index is close to that of the surrounding medium. Simple Mie-scattering models demonstrate that the strength of this opacity dip is sensitive to the size distribution of particles between 1 and 100 microns across. Furthermore, the spatial resolution of the occultation data is sufficient to reveal variations in the transmission spectra within and among these rings. For example, in both the Encke Gap ringlets and F ring, the opacity dip weakens with increasing local optical depth, which is consistent with the larger particles being concentrated near the cores of these rings. The strength of the opacity dip varies most dramatically within the F ring; certain compact regions of enhanced optical depth lack an opacity dip and therefore appear to have a greatly reduced fraction of grains in the few-micron size range.Such spectrally-identifiable structures probably represent a subset of the compact optically-thick clumps observed by other Cassini instruments. These variations in the ring's particle size distribution can provide new insights into the processes of grain aggregation, disruption and transport within dusty rings. For example, the unusual spectral properties of the F-ring clumps could perhaps be ascribed to small grains adhering onto the surface of larger particles in regions of anomalously low velocity dispersion.

42 pages, 15 figures, accepted for publication in Icarus. A few small typographical errors fixed to match correction in proofs

References in corpus (3)

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• The Architecture of the Cassini Division
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Cited by in corpus (15)

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• The Brightening of Saturn's F Ring
• Of Horseshoes and Heliotropes: Dynamics of Dust in the Encke Gap
• A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings
• Occultation observations of Saturn's rings with Cassini VIMS
• Analysis of Clumps in Saturn's F Ring from Voyager and Cassini
• The Vertical Structure of the F Ring of Saturn from Ring-Plane Crossings
• A Detailed Numerical Analysis of Asymmetrical Density Distribution in Saturn's F ring During an Encounter with Prometheus
• A curious ringlet that shares Prometheus' orbit but precesses like the F ring
• On the tidal environment of an outwardly migrated F-ring
• Prometheus Induced Vorticity In Saturns F Ring
• Higher order mass aggregation terms in a nonlinear predator-prey model maintain limit cycle stability in Saturn's F ring
• Changes in a Dusty Ringlet in the Cassini Division after 2010