Energetic nitrogen ions within the inner magnetosphere of Saturn

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Read Full Article (file size: 1988180 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A09223, doi:10.1029/2004JA010509, 2006 Energetic nitrogen ions within the inner magnetosphere of Saturn E. C. Sittler Jr. NASA Goddard Space Flight Center, Greenbelt, Maryland, USA R. E. Johnson Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA H. T. Smith Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA J. D. Richardson Center for Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA S. Jurac Center for Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA M. Moore NASA Goddard Space Flight Center, Greenbelt, Maryland, USA J. F. Cooper Raytheon Technical Services Company LLC, Reston, Virginia, USA B. H. Mauk Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA M. Michael Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA C. Paranicas Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA T. P. Armstrong Fundamental Technologies, Lawrence, Kansas, USA B. Tsurutani Jet Propulsion Laboratory, Pasadena, California, USA Abstract We investigate the importance of nitrogen ions within Saturn's magnetosphere and their contribution to the energetic charged particle population within Saturn's inner magnetosphere. This study is based on the Voyager observations of Saturn's magnetosphere and Cassini observations. The latter have shown that water group ions dominate both the plasma and energetic particle populations but that nitrogen ions over a broad range of energies were observed at ∼5% abundance level. In the outer magnetosphere, methane ions were predicted to be an important pickup ion at Titan and were detected at significant levels in the outer magnetosphere and at Titan. O⁺ ions were found to be the dominant heavy ion in the outer magnetosphere, ∼60%, with methane ions being ∼30% of the heavy ions and N⁺ being a few percent. The two major sources of nitrogen ions within Saturn's magnetosphere are Titan's atmosphere and primordial nitrogen trapped in the icy crust of Saturn's moons and its ring particles deep within the magnetosphere. It is important to understand the source, transport, and sinks of nitrogen in order to determine whether they have a primordial origin or are from Titan's atmosphere. The energetic component is important, since it can come from Titan, be implanted into the surfaces of the icy moons, and reappear at plasma energies via sputtering obfuscating the ultimate source. As we will show, such implantation of nitrogen ions can produce interesting chemistry within the ice of Saturn's moons. The emphasis will be on the nitrogen, but the oxygen and other water group ions are also considered. We argue that neutral clouds of heavy atoms and molecules within Saturn's outer magnetosphere may be the dominant source of energetic heavy ions observed within the inner magnetosphere. Pickup heavy ions in the outer magnetosphere have energies ∼1–4 keV when born. If they diffuse radially inward, while conserving the first and second adiabatic invariants, they can have energies greater than several hundred keV inside of Dione's L shell. We will show how observations relate to the various sources and acceleration processes such as ionization, collisions, wave-particle interactions, and radial diffusion. Received 29 March 2004; accepted 4 May 2006; published 29 September 2006. Keywords: Saturn; Titan; icy moons; magnetosphere; plasma; energetic particles. Index Terms: 2756 Magnetospheric Physics: Planetary magnetospheres (5443, 5737, 6033); 2732 Magnetospheric Physics: Magnetosphere interactions with satellites and rings; 6275 Planetary Sciences: Solar System Objects: Saturn; 6280 Planetary Sciences: Solar System Objects: Saturnian satellites; 6281 Planetary Sciences: Solar System Objects: Titan. Read Full Article (file size: 1988180 bytes) Cited by Citation: Sittler, E. C., Jr., et al. (2006), Energetic nitrogen ions within the inner magnetosphere of Saturn, J. Geophys. Res., 111, A09223, doi:10.1029/2004JA010509. Copyright 2006 by the American Geophysical Union.

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