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Session 27 - Planets.
Oral session, Wednesday, January 07

[27.07] HST/STIS Imaging of Saturn's Far-UV Aurora

J. T. Trauger, K. R. Stapelfeldt (JPL), J. T. Clarke, G. S. Ballester (U. Mich.), WFPC2 Science Team

We report the first images of Saturn's Far-UV aurora with STIS on board the Hubble Space Telescope in October 1997, revealing details of the auroral emissions from atomic and molecular hydrogen in the northern and southern circumpolar auroral zones. Two STIS imaging modes have been used to provide discrimination between hydrogen Lyman-\alpha and H_2 emissions between 1200-1650 Ångstroms. Both atomic and molecular emissions are seen in the STIS clear imaging mode. The addition of a SrF_2 longpass blocker discriminates against Lyman-\alpha and only the molecular emissions are seen. These images are compared with previous FUV imaging of Saturn's aurora with WFPC2 in October 1995 and October 1994. The observed auroral features have been modeled to unfold the latitude, longitude, and vertical extent of the emissions. We confirm that the auroral emissions are tightly confined to latitudes near 76^\circ in the north and south, with a persistent brightening fixed in local time within the dawn sector. These HST images provide the first new observational insights to the physical mechanisms that power Saturn's aurora since the Voyager encounters sixteen years ago.

Program listing for Wednesday