The Relative Surface Roughness of the two Sides of Iapetus

We apply Cassini ISS (Imaging Science Subsystem) data from the January 1st, 2005 flyby of Iapetus to a surface roughness model originally developed by Buratti and Veverka (1985). Since macroscopic features of topography alter the scattering properties of a planetary surface (Schoenberg, 1925; Hameen-Antilla et al., 1965; Hapke, 1966, 1984; Veverka and Wasserman, 1972; Lumme and Bowell, 1981; Buratti et al., 1985), this model uses the observed scattering behavior to provide a depth to radius factor q quantifying the size of craters on the surface. Relative surface roughness of the low albedo (leading) hemisphere and high albedo (trailing) hemisphere can then be determined by comparing the value for the two hemispheres, and any differences observed will provide an estimate of the depth of the dark material. Our preliminary findings show marked differences in macroscopic roughness between the high and low albedo hemispheres, indicating that the surface on the dark side is much smoother than the bright. Our results further suggest that the dark material is substantial enough to cause significant infilling of the craters on the dark side. Funded by the NASA Space Grant.