inner moons and rings can be products of disruption of several Puck-sized satellites during the last four and half billion years. Every such disruption would have started a collisional cascade that quickly ground almost all large bodies into much smaller particles, including dust. Eventually the majority of mass was lost, and particles survived only in positions that were stabilized by mutual resonances and shepherding. The end product of such a disruptive evolution would be a system of narrow rings. A few moonlets must still be embedded within the rings at present. The maximum size of such moonlets is probably around 10 km. The origin of the dust bands is less problematic. The dust has a very short lifetime, 100–1000 years, and should be continuously replenished by collisions between larger ring particles, moonlets and meteoroids from outside the Uranian system. The belts of the parent moonlets and particles are themselves invisible due to their low optical depth, while the dust reveals itself in forward-scattered light. The narrow main rings and the moonlet belts that create dust bands are expected to differ in particle size distribution. The main rings have more centimeter to meter-sized bodies. Such a distribution increases the surface area of the material in the rings, leading to high optical density in back-scattered light. In contrast, the dust bands have relatively few large particles, which results in low optical depth. Exploration The rings were thoroughly investigated by the Voyager 2 spacecraft in January 1986. Two new faint rings—λ and 1986U2R—were discovered bringing the total number then known to eleven. Rings were studied by analyzing results of radio, ultraviolet and optical occultations. Voyager 2'' observed the rings in different geometries relative to the sun, producing images with back-scattered, forward-scattered and side-scattered light. Analysis of these images allowed derivation of the complete phase function, geometrical and Bond albedo of ring particles. Two rings—ε and η—were resolved in the images revealing a complicated fine structure. Analysis of Voyager's images also led to discovery of eleven inner moons of Uranus, including the two shepherd moons of the ε ring—Cordelia and Ophelia. List of properties This table summarizes the properties of the planetary ring system of Uranus. Notes References External links Uranus' Rings by NASA's Solar System Exploration Uranus Rings Fact Sheet Hubble Discovers Giant Rings and New Moons Encircling Uranus – Hubble Space Telescope news release (22 December 2005) Gazetteer of Planetary Nomenclature –