ARCS AND CLUMPS IN THE URANIAN LAMBDA-RING

Careful reprocessing of the Voyager images reveals that the Uranian la mbda ring has marked longitudinal variations in brightness comparable in magnitude to those in Saturn's F ring and Neptune's Adams ring. The ring's variations show a dominant five-cycle (72-degree) periodicity, although additional structure down to scales of about 0.5 degree is a lso present. The ring's shape is defined by a small overall eccentrici ty plus a six-cycle (60-degree) sinusoidal variation of radial amplitu de around 4 kilometers. Both of these properties can be explained by t he resonant perturbations of a moon at a semimajor axis of 56,479 kilo meters, but no known moon orbits at this location. Unfortunately, the mass required suggests that such a body should have been imaged by Voy ager.