Morrison, S.J., Helfenstein, P., Thomas, P.C., Veverka, J. (2010). "Color Photometry of the Small Saturnian Satellites: Global and Regional Variations on Prometheus and Calypso" American Astronomical Society, DPS meeting #42, #09.05.


Abstract
We investigate color variations of Prometheus and Calypso using recent high resolution calibrated Cassini Imaging Subsystem (ISS) images with the Narrow Angle Camera (NAC) broadband filters UV3 (338 nm) , GRN (568 nm), and IR3 (930 nm) in comparison to those of Pandora, Janus, Epimetheus, and Telesto examined previously (Morrison et al., 2009, DPS 45.04). The average UV3/IR3 ratio values are as follows: Prometheus- 0.47, Pandora- 0.53, Janus- 0.57, Epimetheus- 0.58, Telesto- 0.95, and Calypso- 0.77 with formal uncertainties < 0.01 due to noise. While both Prometheus and Calypso continue the trend of increasing blueness toward the E-ring, Calypso differs in color from Telesto with a lower UV3/IR3 ratio and a mean UV3/GRN ratio value of ~0.7 compared to Telesto's mean UV3/GRN value of ~0.9 despite both being Trojans of Tethys. Calypso's surface also exhibits wider color and albedo variations than on Telesto and distinct UV3-bright units undergoing downslope transport with UV3/IR3 ratio values of ~0.05 greater than the mean. Calypso's mean global CLR (611 nm) albedo at normal incidence and 35 degrees phase is ~13% higher than Telesto's, but its albedo range is broader and overlaps Telesto's. The color differences between these two moons may reflect varying degrees of surface burial and contamination from ring particles.