Near-Infrared Photometry of the Saturnian Satellites during Ring Plane Crossing

The first near-infrared (0.9 μm) photometric observations of Saturn's five medium-sized satellites were obtained during the August 1995 ring plane crossing with Palomar Observatory's 60-in. telescope. The albedos of the satellites are very high, indicating that a very low fraction of dark opaque contaminants is present on their icy surfaces. The geometric albedos for the leading sides of the satellites are Enceladus: 1.02; Tethys: 0.90; Dione: 0.72; and Rhea: 0.76. The geometric albedo of the trailing side of Mimas is 0.72. The amplitudes of the satellites' rotational lightcurves are somewhat less than those measured at visible wavelengths. They range from 0.40 (Dione) to 0.10 (Rhea) to 0.05 (Tethys). Both Enceladus and Mimas are brighter on the trailing side, unlike the other three satellites. These results suggest that the optical properties of all five satellites are determined by interactions with Saturn's E-ring.