Quickly, this is how I've done my "planet ring" image. First I made a photoshop file 512x512 with the quarter of a ring. the ring is only a "noise effect" applied on a black layer.(see the details on pic1) In bryce a create a symetrical lattice, then in the terrain editor I apply my ring image (see pic 2) I adjust the settings (crop, dampen, smoothing) till I get the exact result I'm looking for. (see pic3)