Effects on Satellite and Ring Surfaces of Trapped Radiation in The Uranus Magnetosphere

The in-situ measurements by the Voyager 2 LECP experiment of the trapped magnetospheric radiation at the planet Uranus now permit quantitative assessments of the alteration and darkening of possible carbon-containing volatiles on the surfaces of the satellites and rings. We use for these assessments the laboratory-based measurements of the polymerization and residu-formations of CH sub 4 and CO ices that have been made at Bell Laboratories and the University of Virginia using hydrogen and helium ions over a wide range of incident energies, similar to those comprising the radiation environment of Uranus. We show that the expected times for producing alterations of the surfaces depends upon the location of the satellite/ring in the magneto-sphere. Typically, it can be expected that a freshly-exposed methane-covered surface will be polymerized and and blackened within 103-104 years to depths sufficient to affect even the infrared albedo of the surface. This time is very short on an astrophysical time scale.