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Sources and losses of energetic protons in Saturn's magnetosphere |
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| Authors: | C Paranicas DG Mitchell DC Hamilton N Krupp RE Johnson TP Armstrong |
| Institution: | a The Johns Hopkins University Applied Physics Laboratory, MS MP3-E128, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA b Department of Physics, University of Maryland, College Park, MD 20742, USA c Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany d MSSL, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK e Centre for Planetary Sciences, University College London, Gower Street, London WC1E 6BT, UK f University of Virginia, Thornton Hall, Charlottesville, VA 22904, USA g Heliospheric Physics Lab, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA h Fundamental Technologies, Lawrence, KS 66046, USA |
| Abstract: | We present Cassini data revealing that protons between a few keV and about 100 keV energy are not stably trapped in Saturn's inner magnetosphere. Instead these ions are present only for relatively short times following injections. Injected protons are lost principally because the neutral gas cloud converts these particles to energetic neutral atoms via charge exchange. At higher energies, in the MeV to GeV range, protons are stably trapped between the orbits of the principal moons because the proton cross-section for charge exchange is very small at such energies. These protons likely result from cosmic ray albedo neutron decay (CRAND) and are lost principally to interactions with satellite surfaces and ring particles during magnetospheric radial diffusion. A main result of this work is to show that the dominant energetic proton loss and source processes are a function of proton energy. Surface sputtering by keV ions is revisited based on the reduced ion intensities observed. Relatively speaking, MeV ion and electron weathering is most important closer to Saturn, e.g. at Janus and Mimas, whereas keV ion weathering is most important farther out, at Dione and Rhea. |
| Keywords: | Saturn magnetosphere Saturn satellites Saturn rings Satellites surfaces |
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