Infrared Images of the Uranian Rings

Images of the Uranian rings at a wavelength of 2.2 micrometers, chosen to reduce the problem of scattered light from the planet, have been acquired on several occasions spanning the period 1978-1983. Although individual rings are not resolved in these images, the integrated brightness of the system is observed to vary with azimuth. The phase and amplitude of this variation is found to be consistent with the precession rate and variable width of the epsilon ring, as deduced from stellar occultation data. Quantitative analyses of the brightness variations permit an upper limit of approx. 0.0015 to be pladed on the average normal optical depth of any diffuse inter-ring material. Preliminary absolute calibration of the 1983 data yields an average ring geometric albedo, at 2.2 micrometers, of 0.22 + or - 0.002, consistent with previous estimates. Lastly, the potential use of near-infrared images in searches for faint inner satellites of Uranus is discussed.