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[43.01] An Observation of Saturn's Aurora with HST/STIS

John Trauger (JPL), John T. Clarke, G. E. Ballester (U. Michigan), Karl Stapelfeldt, Robin Evans (JPL), WFPC2 Science Team

HST/STIS observations of Saturn's aurora were carried out in October 1997, using both the imaging and spectroscopic modes, providing access to the auroral emissions from atomic and molecular hydrogen in the northern and southern auroral zones. Two STIS imaging modes were used for discrimination between hydrogen Lyman-\alpha and H₂ emissions between 1200-1650 {Å}ngstroms. Both atomic and molecular emissions are seen in the STIS clear imaging mode, while the addition of a SrF₂ longpass blocker discriminates against Lyman-\alpha to isolate the H₂ molecular emissions. The imaging data were taken in time-tagged mode, providing a clear picture of the movements of auroral emissions over the period of observations. These images extend a baseline of HST observations of Saturn's aurora begun in October 1995 and October 1994 with WFPC2 Wood's filter imagery, but with improved sensitivity and spectral discrimination. We now report that the observed auroral features have been modeled to unfold the latitude, longitude, vertical extent, and radiated power of the emissions. We confirm that the auroral emissions are tightly confined to latitudes near 76^\circ in the north and south, with persistent arc morphology that is roughly fixed in local time, but with slow variations in locally bright emission features and in the mean latitudes of the auroral emissions. These HST/STIS images provide new insights into the physical mechanisms that power Saturn's aurora.