The Composition of Saturn's Rings and Satellites from Cassini VIMS and UVIS

Details The Composition of Saturn's Rings and Satellites from Cassini VIMS and UVIS The Composition of Saturn's Rings and Satellites from Cassini VIMS and UVIS

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p14b..05c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P14B-05

Physics

[6008] Planetary Sciences: Comets And Small Bodies / Composition, [6020] Planetary Sciences: Comets And Small Bodies / Ices, [6055] Planetary Sciences: Comets And Small Bodies / Surfaces, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites

Scientific paper

Spectra of the rings and icy satellites of Saturn from Cassini UVIS and VIMS, covering from ~0.1 to 5.1 microns show both expected and unusual properties. The spectra of all these objects are dominated by absorption and scattering by water-ice grains, variable amounts of a non-ice material that is strongly absorbing with a stronger UV absorption, small and variable amounts of CO2 and trace amounts of CH compounds, trapped H2, and possible trace NH compounds. The dark material seems to contain the trapped H2, CO2 and NH compounds. Classical interpretations of the UV absorber and dark material are varying amounts of tholins and carbon. A newer interpretation is that the main spectral components are ice + nano-grains of metallic iron, and nano-hematite. Iron is an efficient H2 trap. Iron has the highest absorption coefficient we have found, approaching one million per cm at 0.25 microns. Nano-sized grains create both Rayleigh absorption and Rayleigh scattering producing the variable spectral signatures seen in the Saturn system. The large spectral range of combined UVIS + VIMS spectra provide strong constraints on composition and grain size distribution. Spectra of the rings and all icy satellites indicate a large range of ice grain sizes, from tens of microns to sub-micron. Sub-micron ice grains create unusual spectral properties, including decreased reflectance near 5-microns, decreased 3.1-micron Fresnel peak, decreased 2.6-micron reflectance, asymmetric to longer wavelength 2-micron absorption, reduced 1.5/2-micron ice band depth ratio, and enhanced reflectance at shorter wavelengths, all of which are seen in the spectra of the rings and satellites. In the blue/UV, spectra of the rings and satellites depart from that of ice because of the UV absorber. Some spectra of Saturn's rings are very similar to spectra of some locations on icy satellites, indicating common compounds are spectrally active from the rings to Iapetus. Sub-micron ice grains create Rayleigh scattering into the UV which competes with the UV absorber to create the various spectral shapes seen in the Saturn system.

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