Multispectral Terrain Analysis of Europa from Galileo Images

Galileo's Solid State Imaging camera recorded six images at wavelengths from 0.41 to 0.99 μm of Europa's trailing hemisphere (∼1.6 km/pixel resolution) during the G1 orbit (1st orbit—target Ganymede) of the nominal mission. We have photometrically corrected these data and extracted spectra representing Europa's diverse geologic terrains. The goals of the analysis of these spectra are (1) to determine whether Europa's geologic units differ spectrally from one another, (2) to determine the number of color components necessary to explain Europa's dark material spectral behavior, and (3) to examine how europan dark materials may change in color with time. Our data indicate that europan dark spots, lineaments and triple band side materials represent a single “dark” and reddish endmember component. We see no evidence for more than one dark endmember; however the dark endmember seen in these G1 data is probably not a “pure” exposure of europan dark material. Mottled terrains, brighter lineaments, and aging triple bands can be modeled by a mixture of bright plains materials and the dark component. Exposures of europan dark materials may thus be brightening with time, eventually blending into the surrounding bright plains.