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J.B. Dalton (SETI Institute / NASA Ames Research Center)
Telescopic and spacecraft observations indicate the ubiquitous presence of water ice on the surface of Europa. Additional components include hydrogen peroxide and possibly both sulfur dioxide and carbon dioxide. Irradiation by charged particles and possible communication with a convecting interior may also have led to the creation and exposure of additional surface compounds. Disrupted terrains on Europa, including linea, chaos regions, impact basins and significant portions of the trailing hemisphere reveal spectral evidence for an additional component. Near-infrared reflectance spectroscopy from Galileo NIMS (Near-Infrared Mapping Spectrometer) indicates that this material is highly hydrated, as evidenced by strongly asymmetric absorption features attributed to waters of hydration at 1.5 and 2.0 microns.
New laboratory studies of heavily hydrated salts demonstrate that as the number of waters of hydration increases, the similarity to spectral observations of Europa becomes more pronounced. We have conducted cryogenic reflectance spectroscopy of the highly hydrated sulfate compounds epsomite, mirabilite, hexahydrite, bloedite and magnesium sulfate dodecahydrate, measured at temperatures relevant to the surface of Europa (~100K). We present results of these studies, along with modeling results which constrain relative abundances of hydrated materials on Europa. Thus far, no material studied can by itself account for the observed spectral character of the reddish, disrupted Europan terrains. However, there are possible mixtures of materials which give reasonable approximations to the Europa observations, subject to considerations of uniqueness and both physical and chemical viability.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.