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R. N. Clark (USGS), R. H. Brown (U.A.), R. Jaumann (DLR), D. P. Cruikshank (NASA), R. M. Nelson, B. J. Buratti (JPL), T. B. McCord (HIGP/SOEST), T. M. Hoefen, J. M. Curchin (USGS), G. Hansen, K. Hibbits (PSI), K-D. Matz (DLR), K. H. Baines (JPL), G. Bellucci (IFSI, CNR), J.-P. Bibring (U. Paris), E. Bussoletti (U. Navale), F. Capaccioni, P. Cerroni, A. Coradini, V. Formisano (IFSI, CNR), Y. Langevin (U. Paris), D. L. Matson (JPL), V. Mennella (IFSI, CNR), P. D. Nicholson (Cornell U.), B. Sicardy (Obs. de Paris), C. Sotin (U. Nantes), VIMS Team
The Cassini-Huygens spacecraft encountered Phoebe on June 11, 2004. The Visual and Infrared Mapping Spectrometer (VIMS) obtained spatially resolved hyperspectral images of Phoebe at 352 wavelengths (0.4-5 microns) from 8:47 UT June 11, 2004 at at an initial range of 245,833 km and phase angle of 84.9 degrees, to 10:22 UT June 12, 2004 at a final range of 338,401 km and a phase angle of 92.2 degrees. The closest image was obtained on June 11 at 19:32 UT at a range of 2,178 km and solar phase angle of 24.6 degrees. The spatial mapping of the VIMS, with an instantaneous field of view of 0.25 by 0.5 milliradian resulted in spatial coverage at full spectral resolution as small as 1 km/pixel. The spatially resolved spectra of Phoebe indicate a low surface albedo, from <1 to ~6 absorption features due to materials which occur with variable abundances and/or grain sizes in different locations on the body. These include: water ice (previously identified by Owen et al, 1999), bound water, and trapped CO2. A broad 1-micron feature is interpreted to be due to Fe2+ bearing minerals. Water ice is observed with absorptions at 3.1, 2, 1.5, 1.25, and 1.04 microns. Variable absorption strengths indicate a variety of ice abundances ranging from almost non detect to >50 than a few hundred microns. Absorptions located in the 3.3 and 1.7 micron region indicate the presence of organic molecules, and a prominent absorption at 2.42 microns is best explained by a cyanide compound. Spectral structure at 4.8-5 microns is also consistent with cyanide compounds. Absorptions at 4.5, 3.3 and 1.7 microns indicate a probable nitrile compound. These compounds argue for either an outer solar system origin for Phoebe, or that its surface has been coated with outer solar system materials.
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The author(s) of this abstract have provided an email address for comments about the abstract: rclark@usgs.gov
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.