The leading hemisphere is very dark and reddish in color at visible-near-IR wavelengths. The bizarre appearance of Iapetus has long intrigued researchers of this Saturnian moon. Iapetus and Phoebe as Measured by the Cassini UVIS Additional information is contained in the original extended abstract. This suggests possible mineralogical differences across the surface of this Saturnian satellite. A 0.67-micron absorption feature is seen in one of the two new spectra. We present two new dark material spectra of Hyperion compared with previously published dark material spectra of Hyperion and Iapetus. Hyperion's Dark Material: Rotational Variation High resolution reflectance spectra have been obtained of the Saturnian satellites Phoebe and Hyperion, the main candidates for a circumsaturnian origin of the Iapetus dark material. The spectral difference between two opposite sides of Phoebe suggests that an impact fragmented Phoebe's parent body, producing Phoebe at the junction of two different compositional units. The opposite side of Phoebe was covered by the other two observations. On two nights covering the same side of Phoebe, the photometry tested positively for an absorption feature centered at 0.7 mu m due to oxidized iron in phyllosilicates. Broadband photometry of Phoebe using ECAS filters was acquired on four nights in 1982 (Tholen and Zellner, Icarus, 1983). We confirm the strong, positive spectral slope attributed to organic material. These absorption features are attributed to (6) A1 -> (4) T2(G) and (6) A1 -> (4) T1(G) charge transfer transitions in minerals such as goethite and hematite that are products of the aqueous alteration of anhydrous silicates. A slight inflection covering 0.4 to 0.6 mu m and a change in slope near 0.73 mu m suggesting the lower wavelength edge of an absorption are also present. A distinct absorption feature centered at 0.67 mu m is apparent in the spectrum. J.Ī linear mixing model has been used to separate the high-resolution visible/near-infrared reflectance spectrum of the Iapetus dark material from spectra of the leading and trailing sides of Iapetus. The Composition of the Iapetus Dark Material, Hyperion and Phoebe These absorption features are attributed to the (6)A(sub 1) yields (4)T(sub 2)(G) and (6)A(sub 1) yields (4)T(sub 1)(G) ferric charge transfer transitions in iron alteration minerals such as goethite and hematite that are products of the aqueous alteration of anhydrous silicates. These absorptions are very similar to those identified in the spectrum of the dark material on the surface of Iapetus, suggesting that the dark material on these two satellites is compositionally similar and has a similar origin. A slight inflection near 0.4 - 0.6 micron and change in slope near 0.73 micron suggesting the lower wavelength edge of an absorption are also present. A distinct absorption feature centered at 0.67 micron is present. We use a linear mixing model to separate the reflectance spectrum of the dark material on Hyperion from the icy material. The spectrum of Hyperion shows the strong spectral slope apparent in spectra of many outer Solar System materials and attributed to organics. The spectrum of Phoebe is similar to the spectrum of a C-class asteroid, with an absorption feature centered near 0.43 micron superimposed on the UV/blue intervalence charge transfer transition present in the spectrum. Narrowband reflectance spectra of the Saturnian satellites S VII Hyperion and S IX Phoebe were obtained across the 0.4 - 0.8 micron spectral region. Are Hyperion and Phoebe Linked to Iapetus?
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