Plasma, Neutral Atmosphere, and Energetic Radiation Environments of Planetary Rings

Cooper, J. F.; Johnson, R. E.; Kollmann, P.; Roussos, E.; Sittler, E. C.

doi:10.1017/9781316286791.014

Cited by 6 publications

(19 citation statements)

References 191 publications

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“…Kollmann et al () modeled the radiation belt fluxes with the assumption that this increase arose from the source neutron spectrum, but the present work rules that out for neutrons from the main rings. This confirms the similar result of Cooper et al () for the ring neutrons, but they also found no large low‐energy increase in fluxes of neutrons from GCR interactions in Saturn's upper atmosphere. Any actual increase in the proton fluxes below 10 MeV, if not from penetrating radiation background in the low‐energy proton channels, would then need to come either from non‐CRAND sources such as local ionization and trapping of energetic neutral atoms from the magnetosphere or from energy‐dependent time evolution of the proton spectrum during trapping.…”

Section: Model Resultssupporting

confidence: 91%

“…Although Cooper (1983) originally did similar calculations with the approximation of the ring material as uniformly thick slabs of ice, we follow Blake et al (1983) in using ice spheres as radiation targets. Cooper et al (2018) have shown that the same results for secondary neutron fluxes at the 20-GeV vertical cutoff are obtained from an ice sphere of radius r = 75 cm as compared to an ice slab of thickness σ = 100 cm, consistent with σ = 4r/3 for the average column thickness of a sphere. Further results reported here extend that comparison for slabs equivalent to 300-and 1,000-cm spheres.…”

Section: Model and Measurement Approachsupporting

confidence: 67%

“…However, our calculation above is for omnidirectional emission of >100 gamma ray photons from the rings. However, Blake et al (), as later discussed by Cooper et al (), showed in the comparable case of neutrons that the fluxes would be highly directional with peak flux tangential to the ring plane. This is because the density of ring body sources in the field of view is more concentrated at tangential rather than vertical angles to the ring plane.…”

Section: Discussionmentioning

confidence: 93%

“…There is also the problem that GCR fluxes and the resultant radiolytic production rates of O 2 gas would be highest at the 2009 solar activity minimum when the measured O 2 densities were at minimum levels. A solution to this problem could be that GCR‐driven radiolysis in the volume ring ice could be biased against O 2 production (Cooper et al, ) in favor of other oxidants such as H 2 O 2 that cannot escape from the ice at seasonally varying ring temperatures below 80 K. These trapped oxidants could then oxidize hydrocarbon contaminants in the rings to produce escaping mass‐28 CO molecules that are detected in the outer magnetosphere as CO + ions (Christon et al, ). In any case, the observed O 2 + density and its seasonal variation in the inner magnetosphere does not constrain the total ring mass and the maximum sizes of ring bodies.…”

Section: Discussionmentioning

confidence: 99%

“…An updated review of the ring plasma and energetic radiation environment has recently been published by Cooper et al (), including new calculations for energetic particle and gamma ray photon emissions at 10 keV to 1 TeV from the inner section of the A ring for the 20‐GeV energy threshold of GCR proton irradiation. The present paper expands on these calculations for ring emission spectra closer to Saturn in the B, C, and D rings at higher vertical cutoff energies for ring body sizes now extending down to 1 cm in radius.…”

Section: Introductionmentioning

confidence: 99%

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Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings

Cooper

Sturner

2018

JGR Space Physics

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Saturn's main rings have an energetic particle and gamma ray photon radiation environment produced by ring interactions of galactic cosmic ray (GCR) protons and heavier ions penetrating the planetary dipolar magnetic field. Accurate models of this radiation environment are important for interpretation of Pioneer 11 and Cassini in situ measurements near the rings and for constraints on radiolytic contributions to neutral gas production and ice chemistry. A GEANT (GEometry ANd Tracking) based simulation is used to model flux spectra of protons, electrons, positrons, charged pions, neutrons, and gamma ray photons emitted from GCR interactions with H2O ice spheres approximating the ring material. Dependent on location in the A to D rings within the planetary magnetic field of Saturn, only GCR protons above respective energies of 20 to 72 GeV can reach the rings without being deflected away by the magnetic field. Calculated differential and integral fluxes from our simulations have good agreement with in situ Pioneer‐11 measurements in selected energy channels. The charged particle and neutral radiation measurements are sensitive, respectively, to the sizes and areal mass densities of ring bodies. Computed gamma ray emission fluxes are 8% of our calculated limit for detection from the Earth by the Fermi Large Area Telescope. Addition of charged particle sensors and neutron‐photon imaging spectrometers to a future Saturn Ring Observer mission would provide valuable information on the ring mass structure. The present paper provides a foundation for modeling of Pioneer 11 and Cassini radiation measurements across the main rings and future measurements of radiation from the rings.

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Section: Model Resultssupporting

confidence: 91%

Section: Model and Measurement Approachsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings

Cooper

Sturner

2018

JGR Space Physics

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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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A radiation belt of energetic protons located between Saturn and its rings

Roussos

Kollmann

Krupp

et al. 2018

Science

Self Cite

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Saturn has a sufficiently strong dipole magnetic field to trap high-energy charged particles and form radiation belts, which have been observed outside its rings. Whether stable radiation belts exist near the planet and inward of the rings was previously unknown. The Cassini spacecraft’s Magnetosphere Imaging Instrument obtained measurements of a radiation belt that lies just above Saturn’s dense atmosphere and is decoupled from the rest of the magnetosphere by the planet’s A- to C-rings. The belt extends across the D-ring and comprises protons produced through cosmic ray albedo neutron decay and multiple charge-exchange reactions. These protons are lost to atmospheric neutrals and D-ring dust. Strong proton depletions that map onto features on the D-ring indicate a highly structured and diverse dust environment near Saturn.

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Plasma, Neutral Atmosphere, and Energetic Radiation Environments of Planetary Rings

Cited by 6 publications

References 191 publications

Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings

Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings

The Composition of Saturn’s Rings

A radiation belt of energetic protons located between Saturn and its rings

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