Evidence from IUE for Spatial and Temporal Variations in the Surface Composition of the Icy Galilean Satellites
Over a decade ago IUE measured the UV spectra of the icy Galilean satellites as a function of longitude (Nelson 1982, Lane et al. 1981, Ockert et al. 1987). Comparisons with new IUE observations taken in 1995 through 1996 explore possible decadal temporal variations. Europa: There have been no variations in the UV spectra of Euroop's trailing side in the past decade. The sulfur dioxide signature seen by Lane et al. (1981) is still evident. Slight variations of 10% to 15% in composition over the past decade are seen on the Jupiter facing and leading hemispheres, but none are detected on the trailing side. Both sets of IUE observations show longitudinal compositional variations. Ganymede: Both sets of IUE observations demonstrate leading vs trailing side compositional variations. The reflectance increases between 240 and 340nm from leading to trailing side. There is a factor of 2 darkening of the trailing side in this wavelength region as one goes to shorter wavelengths. This is not indicative of the characteristics of pure water ice. Neither IUE or HST (Noll et al. 1996) detect any sulfur dioxide absorption at 280nm. The spectra indicate a possible weak absorber in the 240 to 260nm region, and its presence appears stronger in the newer dataset. There is also evidence for decadal temporal variations on the hemisphere centered at 150 degrees longitude. Callisto: The current IUE observations demonstrate a definite variation in composition as a function of longitude. Not all of the former IUE observations have been reprocessed with the new calibration software, therefore complete coverage of this satellite is not currently available. The coverage we do have shows evidence for temporal variations on the hemisphere centered at 300 degrees longitude.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996