The Statistical Morphology of Saturn's Equatorial ENA Projections

Saturn's magnetosphere is an efficient emitter of Energetic Neutral Atoms (ENAs), given the presence of an extended neutral cloud that originates from Enceladus. The ENA emission is symptomatic of the global circulation of plasma in Saturn's magnetosphere. Energetic ions are injected from the outer magnetosphere following magnetotail dynamics and reconnection events. These ions charge exchange with the neutral cloud (confined mostly to the spin plane), producing ENAs. The global ENA emission is dynamic, displaying sudden brightening on the nightside, and discrete rotating enhancements which circle the planet for many hours as energetic ions drift with the bulk plasma flow.

Our characterization of the ENA emission at Saturn is made possible using imagery from the Ion-Neutral Camera (INCA) that flew onboard Cassini. Observations were made over the entire mission lifetime. We present an analysis of the complete INCA image set, using equatorial projections of the flux distribution to reveal the time-averaged morphology of Saturn's ENAs. A comprehensive algorithm was used to calibrate, clean and project all high-inclination orbit days. In the average pictures, many of the projected pixels consist of tens to hundreds of days continuous exposure, captured with a line-of-sight >50° elevation and within 30 R_S distance from the spacecraft.