Europa’s disk-resolved ultraviolet spectra: Relationships with plasma flux and surface terrains

Abstract

The full set of high-resolution observations from the Galileo Ultraviolet Spectrometer (UVS) is analyzed to look for spectral trends across the surface of Europa. We provide the first disk-resolved map of the 280 nm SO 2 absorption feature and investigate its relationship with sulfur and electron flux distributions as well as with surface features and relative surface ages. Our results have implications for exogenic and endogenic sources. The large-scale pattern in SO 2 absorption band depth is again shown to be similar to the pattern of sulfur ion implantation, but with strong variations in band depth based on terrain. In particular, the young chaos units show stronger SO 2 absorption bands than expected from the average pattern of sulfur ion flux, suggesting a local source of SO 2 in those regions, or diapiric heating that leads to a sulfur-rich lag deposit. While the SO 2 absorption feature is confined to the trailing hemisphere, the near UV albedo (300–310 nm) has a global pattern with a minimum at the center of the trailing hemisphere and a maximum at the center of the leading hemisphere. The global nature of the albedo pattern is suggestive of an exogenic source, and several possibilities are discussed. Like the SO 2 absorption, the near UV albedo also has local variations that depend on terrain type and age.