Multispectral Analysis and Photometry of Galileo Europa Data
Jupiter's moon Europa likely possesses an ocean of liquid water beneath its icy surface, but estimates of the thickness of the surface ice shell vary from a few kilometers to tens of kilometers. Color images of Europa reveal the existence of a reddish, non-ice component associated with a variety of geological features. The composition and origin of this material is uncertain, as is its relationship to Europa's various landforms. Published analyses of Galileo Near Infrared Mapping Spectrometer (NIMS) observations indicate the presence of highly hydrated sulfate compounds. This study uses additional spectral information from the Galileo Solid State Imager (SSI) to further elucidate the nature of the surface deposits, particularly when combined with information from the NIMS. Previously, little effort has been focused on this approach because proper calibration of the color image data is challenging, requiring both skill and patience to process the data and incorporate the appropriate scattered light correction. In this study we apply radiometric correction of the SSI data set to enable the use of photometric modeling to understand surface properties such as porosity, density, fine structure and phase response. We properly calibrate then utilize SSI data in combination with NIMS data to compare the non-ice component across Europa's surface to examine possible variations associated with geological features. Detailed comparisons between color data and the morphology of geological features permits improved understanding of the origin and subsequent alteration of non-ice materials. This synthesis of Europa multispectral observations allows us to better understand the composition and possible formation mechanisms of features on Europa's surface associated with non-ice regions. Moreover, by applying the scattered light correction to the Galileo SSI color data set and contributing those corrected data to the PDS, we enable future additional utilization of a valuable data resource.