Discovery of nitrogen in Saturn's inner magnetosphere

Abstract

We detected N+ in Saturn's magnetosphere in the range L ∼ 3.5 to ∼9.5 Saturn Radii (Rs) using data collected by the Cassini Plasma Spectrometer during Saturn Orbit Insertion and the following orbit (Rev A). The presence of N+ in Saturn's magnetosphere has been a source of much debate since Voyager's detection of unresolved mass/charge 14–16 amu ions in this region. Two principal nitrogen sources have been suggested: Titan's atmosphere and nitrogen compounds trapped in Saturn's icy satellite surfaces (Sittler et al., 2004; E. C. Sittler et al., Energetic nitrogen ions within the inner magnetosphere of Saturn, submitted to Journal of Geophysical Research, 2004). The latter may contain primordial nitrogen, likely as NH3 in ice (Stevenson, 1982; Squyers et al., 1983) or N+ that has been implanted in the surface (Delitsky and Lane, 2002). In addition to our nitrogen detection results, we also present an initial examination of possible sources of these ions.