HR: 10:50h
AN: P52A-03    [Abstracts]
TI: Sources for the Radiation Environment of Saturn's Main Rings and the Innermost Radiation Belt
AU: Maurice, S
EM: sylvestre.maurice@cesr.fr
AF: Centre d'Etude Spatiale des Rayonnements, Observatoire Midi-Pyr‚n‚es, 9, av. du colonel Roche, Toulouse, 31400 France
AU: * Cooper, J F
EM: jfcooper@pop600.gsfc.nasa.gov
AF: Raytheon Technical Services Company LLC, SSDOO Project, Code 632, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Johnson, R E
EM: rej@virginia.edu
AF: University of Virginia, Engineering Physics, Thornton Hall, Room B103, Charlottesville, VA 22904 United States
AU: Sittler, E C
EM: edward.c.sittler@nasa.gov
AF: NASA Goddard Space Flight Center, Code 692, Greenbelt, MD 20771 United States
AB: The energetic and plasma charged particle environment around and inwards of Saturn's main rings in the innermost radiation belt has sources from cosmic ray albedo neutron decay (CRAND), charge stripping of neutral atoms from the magnetosphere and gas clouds and tori beyond the main rings, and direct production of secondary charged particles from the same source as CRAND, high-energy cosmic ray interactions with icy ring bodies. Cosmic ray interactions with the planet's upper atmosphere provide an additional but weaker source of neutrons for the ring environment. Charged particle sputtering on ring body surfaces contributes to the neutral atmosphere extending from within the rings outward into the Saturn magnetosphere, and the CRAND source populates the higher energy proton and electron radiation belts in the magnetosphere. Radial distributions for remotely measurable surface composition by Cassini on ring bodies may be due in part to interactions with the radiation belt components and sources. Trapped particle radiation within the main ring region and towards the upper atmosphere of Saturn has been partly explored by the Pioneer 11 spacecraft in-situ in 1979 (e.g., Chenette et al., 1980; Cooper, 1983; Cooper et al., 1985), and more recently by Cassini, in-situ during Saturn orbit insertion and remotely by energetic neutral atom emissions. Gamma ray emissions at Pioneer 11 from the rings were reported by Cooper et al. (1985) and contributed with charged particle data to determination, independent from Voyager ring imaging, of the A and B ring mass column densities. Voyager and earth-based ultraviolet observations measured neutral cloud densities over and beyond the rings, and Voyager plasma instrumentation surveyed the associated pickup ion populations in the magnetosphere. Future missions could increase main ring coverage with spectroscopic x-ray, gamma-ray, and neutron emission measurements and provide new information on ring body composition and mass distribution. Within these rings the loss rates of trapped charged particles are high, but much larger fluxes could accumulate inwards of the B ring towards Saturn, similar to the well-known inner radiation belt and low-altitude equatorial belt of energetic particles at Earth. Diffusion models also predict that radial transport times would be relatively large in this region, probably largest for higher energy trapped particles and resulting in significant fluxes above the planetary atmosphere. Available data and models for particle flux spectra from Pioneer 11, Voyager, and later measurements will be used to estimate time scales for significant radiation chemistry effects on ring particles and in Saturn's upper atmosphere. Improved modeling of surface sputtering and energetic particle interactions for the rings will provide better models for neutral atom and CRAND contributions respectively to the Saturn neutral cloud and magnetospheric hot plasma environments beyond the rings. References: Chenette, D. L., et al., JGR, 85, 5785-5792, 1980 ; Cooper, J. F., JGR, 88, 3945-3954, 1983; Cooper, J. F., et al., JGR, 90, 3415-3427, 1985.
DE: 6265 Planetary rings
DE: 2104 Cosmic rays
DE: 2720 Energetic particles, trapped
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 2756 Planetary magnetospheres (5443, 5737, 6030)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting