Inner Magnetospheric Nitrogen Source Detected at Saturn

The Cassini Plasma Spectrometer (CAPS) detected low energy N+ in Saturn's inner magnetosphere (3.5 < L < 9.5), providing the first evidence for the presence of neutral nitrogen that is locally ionized in this region. We have detected nitrogen ions during 10 orbits when Cassini passed through the inner magnetosphere. Voyager's detection of unresolved mass/charge 14-16 amu/e ions in this region caused much debate over the possible presence of N+ in Saturn's magnetosphere, however CAPS can distinguish between N+ and water group ions. Two principal nitrogen sources have been suggested: material from Titan's atmosphere and nitrogen compounds trapped in the icy satellite and ring particle surfaces (e.g., Sittler et al 2004a, b; Smith et al. 2004). However, with CAPS we have not been able to detect N+ further than |sim9.5 Rs from Saturn while Titan is over 20 Rs away. Additionally, the N+ average energies are low and indicative of local pick-up ion sources. This indicates a nitrogen source connected directly with the icy satellites or from grains from the icy satellites. This may be primordial nitrogen (e.g. NH3 in ice; Stevenson 1982; Squyers et al. 1983) or nitrogen that has been implanted in the surface (Delitsky and Lane 2002). Here we present CAPS N+ observations and show that the immediate nitrogen source and describe the connection is likely to be the icy satellites and/ or E-ring (Young et al. 2005; Smith et al. 2005a).