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[40.23] Energetic Nitrogen Ions within the Inner Magnetosphere of Saturn

E. C. Sittler (NASA/GSFC), R. E. Johnson (UVA), J. D. Richardson, S. Jurac (MIT), M. Moore, J. F. Cooper (NASA/GSFC), B. H. Mauk (JHU/APL), H. T. Smith, M. Michael (UVA), C. Paranicus (JHU/APL), T. P. Armstrong (Fundamental Technologies, LLC), B. Tsurutani (NASA/JPL), J. E. P. Connerney (NASA/GSFC)

Titan's interaction with Saturn's magnetosphere will result in the energetic ejection of atomic nitrogen atoms into Saturn's magnetosphere due to dissociation of N₂ by electrons, ions, and UV photons. The ejection of N atoms into Saturn's magnetosphere will form a nitrogen torus around Saturn with mean density of about 4 atoms/cm³ with source strength of 4.5x10²⁵ atoms/sec. These nitrogen atoms are ionized by photoionization, electron impact ionization and charge exchange reactions producing an N⁺ torus of 1-4 keV suprathermal ions centered on Titan's orbital position. We will show Voyager plasma observations that demonstrate presence of a suprathermal ion component within Saturn's outer magnetosphere. The Voyager LECP data also reported the presence of inward diffusing energetic ions from the outer magnetosphere of Saturn, which could have an N⁺ contribution. If so, when one conserves the first and second adiabatic invariant the N⁺ ions will have energies in excess of 100 keV at Dione's L shell and greater than 400 keV at Enceladus' L shell. Energetic charged particle radial diffusion coefficients are also used to constrain the model results. But, one must also consider the solar wind as another important source of keV ions, in the form of protons and alpha particles, for Saturn's outer magnetosphere. Initial estimates indicate that a solar wind source could dominate in the outer magnetosphere, but various required parameters for this estimate are highly uncertain and will have to await Cassini results for confirmation. We show that satellite sweeping and charged particle precipitation within the middle and outer magnetosphere will tend to enrich N+ ions relative to protons within Saturn's inner magnetosphere as they diffuse radially inward for radial diffusion coefficients that do not violate observations. Charge exchange reactions within the inner magnetosphere can be an important loss mechanism for O⁺ ions, but to a lesser degree for N⁺ ions. Initial LECP results using composition data at energies greater than 200 keV/nucl., showed that heavy ions within Saturn's inner magnetosphere dominated over protons, but that contrary to original suggestions that these ions were O⁺ , we now argue that they are instead N⁺ ions. With energetic N⁺ ions bombarding the icy satellite surfaces chemical reactions can occur at the end of the ion tracks and produce nitrogen oxides or other nitrogen containing molecules such that the radiology within the icy surfaces is driven by the impacting energetic nitrogen ions. These can accumulate over the lifetime of the Saturn system.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.