Statistical analysis of Saturn's UV auroral outer emission

Recent observations of Saturn’s aurora with the UVIS spectrograph on-board Cassini not only confirm the presence of a quasi-permanent partial ring of emission equatorward of the main auroral oval, but they also increase the number of positive cases and allow for a statistical analysis of the characteristics of this outer emission. This faint but distinct auroral feature appears at both hemispheres in the nightside sector. It magnetically maps to relatively large distances in the nightside magnetosphere, on the order of 9 RS. It was initially thought that pitch angle scattering of electrons into the loss cone by whistler waves would be responsible for the outer auroral emission. Rough estimates suggested that a suprathermal electron population observed with Cassini in the nightside sector between 7 and 10 RS might power this process. However, a new analysis of 7 years of Cassini electron plasma data indicates the presence of layers of upward and downward field aligned currents. They appear to be part of a large-scale current system involving dayside-nightside asymmetries as well as trans- hemispheric variations. This system comprises a net upward current layer, carried by warm electrons, limited to the nightside sector which may as well generate the outer UV auroral emission. The growing dataset of UVIS spectro- images is used to find any such asymmetries in the outer auroral emission.