Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusm.p32a..04h&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #P32A-04
Other
6020 Ices, 6280 Saturnian Satellites
Scientific paper
Enceladus' reflectance spectrum, while being very bright at VNIR wavelengths and consistent with a surface composed primarily of H2O ice, is darker at far-UV wavelengths than predicted by pure H2O ice spectral models. The visible spectrum of Enceladus is bright and featureless, like pure water ice, and the near-IR spectrum has also been compared to pure water ice (Cruikshank et al., 2005) or pure water ice plus a small amount of NH3 hydrate (Verbiscer et al., 2006) or NH3 (Emery et al., 2005). We investigate the darkness of the FUV spectrum by examining existing laboratory measurements of the optical constants and reflectance spectra of H2O and other candidate species, and by comparing with spectral models. We find that the FUV darkness of Enceladus can be explained by the presence of a small amount of NH3 and a small amount of a tholin in addition to H2O ice. (Optical constants for NH3 hydrate in the UV are not available but we expect that the gross spectral properties are similar to those of NH3 and cannot rule out the presence of NH3 hydrate rather than NH3.) The presence of these three species (H2O, NH3 and a tholin) appears to satisfy not only the FUV darkness and spectral shape, but also the visible wavelength brightness and spectral shape. We expect that ammonia in the Enceladus plume condenses in the E-ring, grains of which accumulate on and coat the surface Enceladus throughout its orbit, constantly enhancing the visible brightness of the moon and resupplying a small amount of NH3 to the surface.
Hansen Camilla Juul
Hendrix Amanda R.
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