IUES DETECTION OF TENUOUS SO2 FROST ON GANYMEDE AND ITS RAPID TIME VARIABILITY

International Ultraviolet Explorer (IUE) observations of Ganymded demo nstrate decade length or less temporal variations at a few discreet tr ailing side longitude regions. The temporal changes are seen in compar isons of IUE spectra from 1984-1986 with new IUE observations from 199 6. Variations are observed on the trailing side associated with the ne w detection of SO2 frost. A distinctive SO2 frost spectral signature a t 0.32 mu m is detected in the 1984-1986 spectra of trailing side regi ons from 2.25 degrees to 285 degrees which are absent in corresponding 1996 measurements.