Tethys: Modeling of Near Infrared Telescopic Observations

We have analyzed near-infrared telescopic spectral observations of Tethys for comparison to Cassini observations. A mixture modeling code based on Hapke theory (Hapke, 1981, 1993) has been adapted and combined with an iterative simplex algorithm (Press et al., 1992; Bauer et al., 1998) and applied to observations of Tethys. The mnodel can treat spectra as nonlinear mixtures of various grain sizes and compositions, as linear mixtures of adjacent spatial regions, or a coimbination of both. We have assembled from various sources (Ockman, 1957; Warren, 1984; Hudgins et al., 1993; Grundy and Schmitt, 1998) water ice optical constants for the near-infrared spectral range for temperatures of 70, 80, 90, and 100 K. Preliminary results indicate that telescopic spectra of Tethys are best matched by crystalline water ice with a range of grain sizes, with a small complement of dark material such as amorphous carbon.