What Mechanism Appears to Have Made the Surfaces of Many

What mechanism appears to have made the surfaces of many moons and the particles in the ring material of the outer planets very dark?

A) collection of large amounts of fine dust, perhaps carbon dust or soot, from interplanetary space
B) long-term bombardment by electrons and ions in the magnetosphere: radiation darkening
C) burning and charring of the surfaces by successive passages through the planet's atmosphere, similar to the formation of dark fusion crusts on meteorites that have hit Earth
D) chemical changes that are caused by long-term exposure to solar ultraviolet radiation