ENA generation mechnism Krimigis et al, 2004 Some Questions about the Interaction between Trapped Particles and Neutrals l What is the source of trapped particles? l How are they accelerated to high energies? l What is the principal loss mechanism? l How do particles respond in the rotating magnetic field of Saturn? l Are particle collisions with ring and icy moon surfaces important? ENA generation mechnism Energetic Neutral Atom (ENA) Imaging O + fast + H O fast + H + Grid outlines INCA FOV Hydrogen Oxygen ENA emission modulated at Saturns rotation period ENA PERIODICITIES With what else does this ENA oscillation correlate? Energetic (25-200keV) e - B-field SKR Oxygen ENA modulation is time- dispersed in energy--high energies lead low, due to grad-B drifts At what radial distance is the corotating ENA emission concentrated? 7 R s Highest ENA production The density of OH in the 6-10 Rs region is comparable to H density in the Geocorona. O is probably about the same as OH. O+ lifetime in the Earths ring current is ~ 8h. O+ lifetime in the inner Saturn magnetosphere could be much shorter, depending on its radial placement (O, OH charge-exchange cross-section is larger than H) Hydrogen Geocorona Rairden et al. (1986) Earth Ring Current Devoid of energetic ions Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini (Mauk et al, GRL, June 2005) Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini Modulation persistence and phase lock suggest an active longitude (could be a quadrant) coupled with a preferred local time for ion injection Neutral Gas? Ion Dispersion Event Gas Hot H+, O+ Saturn Cassini How do these events look from an off-equatorial vantage point? Same event, higher energy H Watch the rotating blob Brightest ENA emission from interface between dense gas cloud in vicinity of E-Ring, and energetic ions just outside that region. Large scale ion injections are commonly seen as corotating brightenings in ENA. Ion injections are well correlated with SKR, including when they are seen repeating at Saturns rotational period. Oxygen ENA emission shows more pronounced, and more regular, rotation modulation than hydrogen. Energetic oxygen lifetime in the inner magnetosphere should be no longer than hours, given the density of the water-product cloud in the vicinity of the E-ring. The repeated, un-damped rotational modulation therefore requires nearly continual replenishment of the energetic oxygen ions. The synchronicity of the modulated ENA emission, as well as the unchanging energy dispersion, requires repeated injections preferentially at the same Saturn IAU longitude --possibly the same clock that drives the SKR. Summary of Observations on Periodicities