HR: 0830h
AN: P51B-0445    [PDF]
TI: The Surface Composition of Europa: Mixed Water, Hydronium, and Hydrogen Peroxide Ice
AU: * Clark, R N
EM: rclark@usgs.gov
AF: U. S. Geological Survey, MS 964 Box 25046 Federal Center, Lakewood, CO 80228 United States
AB: Interpretations of the composition of the surface of Europa have been controversial, with different identifications resulting in correspondingly different implications for the origin and evolution of the satellite. The surface of Europa has an unusual water spectrum that has previously been interpreted as resulting from sulfate and carbonate salt minerals. However, the spectra of such minerals at the temperatures of Europa's surface have features which preclude their presence. This has led some investigators to postulate an unspecified hydrated mineral as the cause, and the term "non-icy" is now generally used to describe the Europa material. Europa's "non-icy" spectrum has also been interpreted as a sulfuric acid hydrate. Sulfuric acid hydrate spectral features are not unique to sulfuric acid, because other acids show similar features. These features are interpreted here as being due to hydronium, H3O, in the ice structure. Thus, Europa's "non-icy" material is interpreted as being due to hydronium. Hydronium ice may be caused by ionization defects in regular ice due to bombardment by magnetospheric particles, implantation of protons in the ice surface, or endogenic processes indicating an acidic ocean, or all three. Hydrogen peroxide also has been identified on Europa, and hydrogen peroxide-acid mixtures provide close matches to Europa's "non-icy" material. This too may be caused by ionization defects from the particle bombardment, or may indicate an ocean of acid and hydrogen peroxide. Spectra of Ganymede and Callisto show spectral characteristics of the Europa water-hydronium-peroxide ice, but with less intensity and are consistent with an exogenic modification of the surfaces by particle bombardment, rather than decreasing amounts of salt and oceanic processes as one moves away from Jupiter. Europa's "non-icy" spectra may be composed of $>$99% ordinary ice that has been disrupted by the particle bombardment, or an acid-hydrogen peroxide mixture composed of about 2/3 water. Liquid acid-hydrogen peroxide mixtures readily attack organic molecules, metals, and other compounds. If a lander melted this surface during its operations, the liquid could attack lander components and destroy experiments. An ocean composed of an acid-hydrogen peroxide mixture is a hostile environment for life as we currently know it.
UR: http://speclab.cr.usgs.gov
DE: 5709 Composition
DE: 5749 Origin and evolution
DE: 5757 Remote sensing
DE: 6008 Composition
DE: 6020 Ice
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting