Saturn's C ring and Cassini division: Particle sizes from Cassini UVIS, VIMS, and RSS occultations

Jerousek, R. G.; Colwell, Joshua; Hedman, Matthew M.; French, R. G.; Marouf, E. A.; Esposito, L. W.; Nicholson, P. D.

doi:10.1016/j.icarus.2019.113565

Cited by 6 publications

(4 citation statements)

References 52 publications

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“…After correcting for this offset, the calculated shadowed altitudes along Cassini's trajectory precisely match the dips in H 2 + density for orbits 288 and 292. We can further compare the estimated mean optical depths for the ringlets/plateaus to those derived from stellar occultations by Jerousek et al (2020), with the values agreeing well (see Table 1). The fact that these narrow ringlets and plateaus, with widths of 70-250 km and calculated altitudinal shadow extents of just 5-16 km along the trajectory of Cassini (traveling at a velocity of ∼34 km s −1 ), are clearly visible in the H 2 + data is consistent with the short-lived nature of these ions (∼0.5 s) and low ion flow speeds near periapsis for orbits 288 and 292.…”

Section: Discussionsupporting

confidence: 64%

“…results of this estimation are listed for the analyzed ringlets/plateaus in Table 1. Considering this simple method, the derived n t agree remarkably well with those derived from stellar occultation measurements by Jerousek et al (2020). The mean optical depths are calculated by taking the mean of the calculated optical depth according to Equation (5) for each H 2 + data point in each shadowing bin.…”

Section: Hsupporting

confidence: 66%

“…This method can be used to calculate the normal optical depth profile across the C ring, as shown in Figure 5. Comparing with Figure 1 in Jerousek et al (2020) shows that our derived estimates for the background optical depth profile generally exceed the stellar occultation measurements by up to a factor of ∼2, but it should be noted that due to the variable H 2 + densities it is impossible to derive a precise background profile. At higher altitudes, photochemical equilibrium does not apply and thus this method would not work for these regions, for example, to estimate the B ring optical depth profile.…”

Section: Hmentioning

confidence: 57%

“…Dips (used further to describe sharp and narrow decreases) in the H 2 + density for the outbound part of orbit 292 were described in Dreyer et al (2021), who suggested ringlet shadowing signatures as a potential explanation, which we will further study here. We adopt the terminology of Colwell et al (2009): ringlets (R) as narrow rings with increased optical depth within gaps where the background optical depth drops to practically zero, embedded ringlets (ER) as regions with prominent increases in optical depth compared to the background optical depth profile (but not offset from it by a gap), and plateaus (P) denoting embedded ringlets with optical depths of τ ∼ 0.4 rising sharply from the background and peak optical depths at the edges (see Figure 1 in Jerousek et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn’s Ionosphere

et al. 2022

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For orbits 288 and 292 of Cassini’s Grand Finale, clear dips (sharp and narrow decreases) are visible in the H 2 + densities measured by the Ion and Neutral Mass Spectrometer (INMS). In 2017, the southern hemisphere of Saturn was shadowed by its rings and the substructures within. Tracing a path of the solar photons through the ring plane to Cassini’s position, we can identify regions in the ionosphere that were shadowed by the individual ringlets and plateaus (with increased optical depths) of Saturn’s C ring. The calculated shadowed altitudes along Cassini’s trajectory line up well with the dips in the H 2 + data when adjusting the latter based on a detected evolving shift in the INMS timestamps since 2013, illustrating the potential for verification of instrument timings. We can further estimate the mean optical depths of the ringlets/plateaus by comparing the dips to inbound H 2 + densities. Our results agree well with values derived from stellar occultation measurements. No clear dips are visible for orbits 283 and 287, whose periapsides were at higher altitudes. This can be attributed to the much longer chemical lifetime of H 2 + at these higher altitudes, which in turn can be further used to estimate a lower limit for the flow speed along Cassini’s trajectory. The resulting estimate of ∼0.3 km s−1 at an altitude of ∼3400 km is in line with prior suggestions. Finally, the ringlet and plateau shadows are not associated with obvious dips in the electron density, which is expected due to their comparatively long chemical (recombination) lifetime.

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Section: Discussionsupporting

confidence: 64%

Section: Hsupporting

confidence: 66%

Section: Hmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

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Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn’s Ionosphere

et al. 2022

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The Composition of Saturn’s Rings

Miller,

Filacchione,

Cuzzi

et al. 2024

Space Sci Rev

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The origin and evolution of Saturn’s rings is critical to understanding the Saturnian system as a whole. Here, we discuss the physical and chemical composition of the rings, as a foundation for evolutionary models described in subsequent chapters. We review the physical characteristics of the main rings, and summarize current constraints on their chemical composition. Radial trends are observed in temperature and to a limited extent in particle size distribution, with the C ring exhibiting higher temperatures and a larger population of small particles. The C ring also shows evidence for the greatest abundance of silicate material, perhaps indicative of formation from a rocky body. The C ring and Cassini Division have lower optical depths than the A and B rings, which contributes to the higher abundance of the exogenous neutral absorber in these regions. Overall, the main ring composition is strongly dominated by water ice, with minor silicate, UV absorber, and neutral absorber components. Sampling of the innermost D ring during Cassini’s Grand Finale provides a new set of in situ constraints on the ring composition, and we explore ongoing work to understand the linkages between the main rings and the D ring. The D ring material is organic- and silicate-rich and water-poor relative to the main rings, with a large population of small grains. This composition may be explained in part by volatile losses in the D ring, and current constraints suggest some degree of fractionation rather than sampling of the bulk D ring material.

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