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H. T. Smith (Univ. of Virginia), E. C. Sittler (NASA GSFC), R. E. Johnson (Univ. of Virginia), D. McComas (Southwest Research Institute), D. Reisenfeld (Univ. of Montana), M. Shappirio (NASA GSFC), M. Michael (Univ. of Virginia), V.I. Shematovich (Inst. of Astronomy, RAS), R. A. Baragiola (Univ. of Virginia), F. Crary, D. Young (Southwest Research Institute)
We are analyzing CAPS instrument data on Cassini to look for nitrogen ions in Saturn’s magnetosphere. Because Voyager could not separate oxygen and nitrogen, there has been considerable controversy on nitrogen’s presence and relative importance. Two principal sources have been suggested: Titan’s atmosphere and nitrogen species trapped in Saturn’s icy satellite surfaces (Sittler et al 2004). The latter may be primordial nitrogen, likely as NH3 in ice (Stevenson 1982; Squyers et al. 1983) or nitrogen ions that have been implanted in the surface (Delitsky and Lane 2002). We will present the results of Saturnian nitrogen cloud modeling and relevant CAPS observations.
We recently described the Titan source (Michael, et al. 2004; Shematovich et al. 2003; Smith et al. 2004; Sittler et al. 2004) in preparation for Cassini’s Saturnian plasma measurements. Two components were identified: energetic nitrogen ions formed near Titan and energized as they diffused inward (Sittler et al. 2004) and neutrals in orbits with small perigee that became ionized in the inner magnetosphere (Smith et al 2004). The latter component would be a source of lower energy, co-rotating nitrogen ions to the inner magnetosphere. Such a component would have an energy spectrum similar to nitrogen species sputtered from the icy satellite surfaces (Johnson and Sittler 1990). However, the mass spectrum would differ, likely containing NHx and NOx species also, and, hence, may be separated from the Titan source.
Our preliminary analysis for nitrogen species in the CAPS data will be compared to the models. Of interest will be the energy spectra, which can indicate whether any nitrogen present is formed locally or near Titan’s orbit and diffused inward.
This work is supported by the NASA Planetary Atmospheres, NASA Graduate Student Research, Virginia Space Grant Consortium Graduate Research Fellowship and the CAPS Cassini instrument team programs.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.