Unraveling the zebra: Clues to the Iapetus dark material composition

A linear mixing model has been used to separate the high-resolution visible/near-infrared reflectance spectrum of the Iapetus dark material from the spectra of the leading and trailing sides of Iapetus. A distinct absorption feature centered at 0.67 mu m is apparent in the spectrum. 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. These absorption features are attributed to the (6)A(1) --> T-4(2)(G) and (6)A(1)--> T-4(1)(G) charge transfer transitions in minerals such as goethite and hematite that are products of the aqueous alteration of anhydrous silicates. We confirm the strong, positive spectral slope attributed to organic material. (C) 1996 Academic Press, Inc.