Small particles and self-gravity wakes in Saturn's rings from UVIS and VIMS stellar occultations

Jerousek, R. G.; Colwell, Joshua; Esposito, L. W.; Nicholson, P. D.; Hedman, M. M.

doi:10.1016/j.icarus.2016.04.039

Cited by 19 publications

(12 citation statements)

References 33 publications

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“…5,6 and 19). Wake parameters including estimates of the ring thickness, have been derived for regions in the A and B rings by Colwell et al (2006), Hedman et al (2007), Colwell et al (2007), Nicholson and Hedman (2010) and Jerousek et al (2016). No such asymmetry is seen in the C ring or Cassini Division, consistent with theoretical models and the lower surface mass densities in these regions.…”

Section: Discussionsupporting

confidence: 59%

“…In at least one occultation by this star observed by both instruments it was possible to confirm the reality of a 500 m-wide clump of some sort in the F ring that occulted both stars (Esposito et al 2008). Comparisons of the optical depths measured simultaneously by both instruments in occultations by these stars have also made it possible to draw useful conclusions about the small end of the ring particle size distribution in some regions (Colwell et al 2014;Jerousek et al 2016), avoiding the complications introduced by the ubiquitous self-gravity wakes.…”

Section: Overview Of Vims Ring Occultationsmentioning

confidence: 82%

“…The High Speed Photometer channel of the Ultraviolet Imaging Spectrometer (UVIS) observed early-type stars through the rings at a wavelength of 150 nm, obtaining radial optical depth profiles with sampling intervals as short as 1 msec, corresponding to a nominal radial resolution as fine as 10-20 m (Esposito et al 2004;Colwell et al 2010;Jerousek et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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Occultation observations of Saturn's rings with Cassini VIMS

Nicholson

Ansty

Hedman

et al. 2020

Icarus

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We describe the prediction, design, execution and calibration of stellar and solar occultation observations of Saturn's rings by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini spacecraft. Particular attention is paid to the technique developed for onboard acquisition of the stellar target and to the geometric and photometric calibration of the data. Examples of both stellar and solar occultation data are presented, highlighting several aspects of the data as well as the different occultation geometries encountered during Cassini's 13 year orbital tour. Complete catalogs of ring stellar and solar occultations observed by Cassini-VIMS are presented, as a guide to the standard data sets which have been delivered to the Planetary Data System's Ring Moon Systems Node (Hedman and Nicholson 2019b).2 Subject to the constraint that only even offsets in Z are permitted. 3 In normal, or 'low-res' mode, the standard 0.5 × 0.5 mrad IR IFOV is actually synthesized by combining two adjacent hi-res measurements. The 0.25 mrad width of the hi-res pixel is set by the width of the spectrometer's entrance slit, while its 0.50 mrad height is set by the physical dimension of the IR pixels.

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Section: Discussionsupporting

confidence: 59%

Section: Overview Of Vims Ring Occultationsmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

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Occultation observations of Saturn's rings with Cassini VIMS

Nicholson

Ansty

Hedman

et al. 2020

Icarus

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“…The methods of the current work use Interactive Data Language (IDL 8.8) and Autodesk Maya software (2018). The relevant parameters involved in the construction of the arrays are the optical depth, τ, and the self-gravity wake ratios for the optically-thick ring regions wake vertical thickness to wake width,

, and wake separation to wake width,

(from estimations by [7] ). The arrays we create do not derive from any N-body dynamical code (such as [8] ), but we create them based on the general structure features derived from observations and must be taken as snapshots of the average structure of selected regions of the main rings, though they implicitly posses dynamical features.…”

Section: Introductionmentioning

confidence: 99%

Methods for ray-tracing thermal modelling of Saturn's main rings

García-Reyes

Flandes

2021

MethodsX

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The thermal emission and temperatures of the main rings of Saturn depend on the energy the ring particles absorb, reflect and scatter and/or on their Bond albedo, emissivity, thermal inertia, rotation rate and porosity. However, the energy that each particle absorbs also depends on the amount of energy (e.g., solar energy) that reaches its surface and this latter on the local optical depth, that controls the mutual eclipsing between neighbouring particles and, in general, all shadowing effects on the rings. On the other hand, thermal models of the rings of Saturn based on the energy balance equation strongly depend on a function that described how the non-shadowed area of ring particles changes with solar elevation. Experimental and analytical shadowing functions have been proposed by [6] and [1] , respectively. In this work, we propose shadowing functions based on the creation of 3D arrays of spherical particles that simulate specific regions of the main rings of Saturn. The methods implemented to obtain these shadowing functions follow the next general steps: • Arrays are created as a collection of spherical particles with a size distribution that follows a power law constrained to the optical depth of the region of study based on the UVIS instrument data. • The particles of the arrays are then reordered to add some relevant dynamical features observed in actual rings (e.g., wake structures in the case of optically-thick rings). • Under different illumination geometries, images of these arrays are rendered using ray tracing. From these images, an analysis of their pixel brightness values allows us to determine the non-shadowed fractional area of the particles in order to compose the corresponding shadowing functions.

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“…So far, there is a limited, but accurate knowledge of some microscopic and macroscopic signatures of the rings from the data taken by various instruments onboard Cassini. The ring optical depth obtained by stellar occultations is a pure macroscopic signature of the ring layer, since its variations contain information that allows retrieval of the size distribution of the ring particles (Zebker, Marouf & Tyler 1985;Jerousek et al 2016), the clumpiness of the rings (Colwell, Esposito & Sremčević 2006;Colwell et al 2007Colwell et al , 2009aHedman et al 2007), and the surface density of the ring layer (Baillié et al 2011;Colwell et al 2009a,b). On the other hand, during the last few years, additional constraints have been derived from the water ice band depths in the near-IR (Nicholson et al 2008;Filacchione et al 2012;Hedman et al 2013).…”

mentioning

confidence: 99%

Cassini CIRS and ISS opposition effects of Saturn’s rings – I. C ring narrow or broad surge?

Déau

Dones

Spilker

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We focus on the thermal and optical opposition effects of Saturn’s C ring seen by Cassini CIRS (Composite InfraRed Spectrometer) at 15.7 ${\mu}$m and ISS (Imaging Science Subsystem) at 0.6 ${\mu}$m. The opposition surge is a brightness peak observed at low phase angle (α → 0°). Saturn rings’ opposition surge was recently observed in reflected light and thermal infrared emission by Cassini. There is debate on whether the C ring’s thermal opposition surge width is narrow (≲1°) or broad (≳30°). This surge is important because its width was used to define the scale of ring properties driving the thermal peak. We parametrize the CIRS and ISS phase curves with several morphological models to fit the surge shape. For five of the largest C ring’s plateaus, we find that their thermal surge is 10 times wider than the optical surge and that the thermal surge width (∼4°) is neither narrow, nor broad. We compare radial differences between CIRS and ISS surge morphologies with the optical depth τ (from UVIS, UltraViolet Imaging Spectrograph) and water ice band depth (from VIMS, Visual and Infrared Mapping Spectrometer) profiles. We find that: water ice band depths (microscopic ring signatures) and τ (macroscopic ring signatures) show respectively little and large contrasts between the background and the plateaus. The thermal surge amplitude and τ are correlated, and we found no band depth dependence, contrary to the optical surge amplitude, which shows no correlation with τ. These correlations suggest a macroscopic scale dominance in controlling the C ring’s thermal opposition effect.

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Small particles and self-gravity wakes in Saturn's rings from UVIS and VIMS stellar occultations

Cited by 19 publications

References 33 publications

Occultation observations of Saturn's rings with Cassini VIMS

Occultation observations of Saturn's rings with Cassini VIMS

Methods for ray-tracing thermal modelling of Saturn's main rings

Cassini CIRS and ISS opposition effects of Saturn’s rings – I. C ring narrow or broad surge?

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