PIONEER-10 ULTRAVIOLET PHOTOMETER OBSERVATIONS OF JOVIAN UV EMISSION IN 1973

The Pioneer 10 ultraviolet measurements obtained during the Jupiter en counter in 1973 have been further examined by using improved data hand ling and analysis techniques. The Pioneer 10 observations of Jupiter a nd its satellites during the encounter have been carefully reviewed in order to improve our understanding of the morphology of the To plasma torus and Jupiter's upper atmosphere and to investigate the possible existence of other emission source such as Europa. In addition, the mo rphology of Io's bimodal torus observed during the Pioneer 10 encounte r has been compared with the Voyager observations obtained approximate ly 6 years after the Pioneer 10 flyby and significant differences in t he torus characteristics are found. The To torus in 1973 was more simi lar to the 1992 Ulysses observations of a longitudinally asymmetric ri ng than to the complete ring observed by Voyager. Pioneer 10 observed a significantly dimmer Io torus and Jupiter upper atmosphere in the EU V compared to the Voyager observations. Apart from the torus and Jupit er, Pioneer 10 observed additional emissions which have been attribute d to Io itself. Three distinct possibilities have been discussed to ex plain these additional emissions. The most likely is that Pioneer 10 o bserved volcanism on Io. There is also evidence of Pioneer 10 observin g emissions from Europa. The present analysis clearly shows that the J ovian system in 1973 was significantly different from that observed in 1979.