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T. McCord (HIGP/SOEST, University of Hawaii), G. Teeter (EMSL, Pacific NW National Laboratory), G. Hansen (HIGP/SOEST, University of Hawaii), M. Soeger, T. Orlando (EMSL, Pacific NW National Laboratory)
A growing body of evidence indicates that an ocean is hidden beneath the icy crust of Jupiter's second moon, Europa. Galileo mission data reveal surface features indicating surface disruption, magnetic fields indicating moving, conducting fluids, and cycloidal cracks likely caused by ocean tides. Spectral evidence from the NIMS indicates hydrated materials, suggested to be salts, on the surface in concentrated deposits closely associated with the fractures and disturbed terrain [McCord et al., 1998, 1999]. Hydrated salts are indicated also by thermal evolution models of Europa's interior and laboratory studies of meteorites [Fanale et al., 1977, 1998; Kargel, 1991]. The hydrated mineral deposits might result from exposing salty ocean water to the surface. To investigate this possibility we prepared frozen sulfate and carbonate brine samples by rapid thermal quenching and measured IR reflectance spectra of these flash frozen brines as a function of hydration level in situ in cold vacuum. Ab intio calculations of intermolecular distances, molecular mechanics simulations of aqueous salt solutions, and the temperature and cooling rate in our experiment indicate the anions should be fully solvated and the average number and configuration of hydration waters in the first solvation shell should be ``frozen in" during deposition. Thus, we should be dealing with frozen brines rather than crystallized minerals. These spectra are even more like the Europa non-ice endmember material spectrum than are previously reported spectra for warm and cold crystalline samples prepared at ambient. Thus, the strengthened spectroscopic evidence, along with geologic evidence, geochemical models and meteorite studies, strongly suggest that a major portion of the non-ice material on Europa that is closely associated with the surface disruption processes is a somewhat disordered hydrated salt-like material that is endogenic in origin. This work is supported by NASA Galileo Mission and JSDAP Program and the Dept. of Energy Basic Energy Sciences Program.
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