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T. W. Momary, K. H. Baines, P. A. Yanamandra-Fisher (JPL/CalTech), L. A. Lebofsky (U.of Arizona), W. Golisch, C. Kaminski (NASA/IRTF)
We report absolutely-calibrated photometry of the Saturnian satellites in canonical near-infrared filters, including the first such spectrum of the leading side of Enceladus. The satellites were observed during Ring Plane Crossing in August and September of 1995 with the NSFCAM instrument at the NASA/IRTF. These observations were also simultaneous with those of the Uranian system, taken with the same instrument and filters, and analyzed by Baines {\it et al.} ({\it Icarus} {\bf 132}, 266-284, 1998). Results are reported for J, H, and K filters near 1.27, 1.62, and 2.20 \mum, and two 0.1 \mum-wide filters centered at 1.73 and 2.27 \mum. We find that Enceladus has a peak brightness at 1.27 \mum with a geometric albedo of 0.898 ± 0.063, in contrast to the Uranian satellites Miranda, Ariel, and Titania, which are relatively dim at this wavelength (albedos of roughly 0.3). The J-H band depth of Enceladus is about 30%, characteristic of spectra of Rhea, Tethys, and the trailing side of Iapetus, taken from Clark {\it et al.} ({\it Icarus} {\bf 58}, 265-281, 1984) and convolved with our filters. By contrast, the darker Uranian satellites display a J-H band depth of less than 10%. From H to 1.73 \mum, the full-disk albedo of Enceladus increases by 27%, similar to the Uranian satellites. The dip in the Enceladus spectrum from J to H, as well as the subsequent rise from H to 1.73 \mum, are an expected signature of water ice. Finally, preliminary results for the albedos of Tethys, Dione, Rhea, and Mimas, as well as Enceladus, at 2.27 \mum compare favorably with the visible albedos of Buratti and Veverka ({\it Icarus}, {\bf 58}, 254-264, 1984).
The author(s) of this abstract have provided an email address for comments about the abstract: momary@aloha.jpl.nasa.gov