Comets
Dirty iceball model
Dirty snowball theory
A model for a cometary nucleus proposed by Fred Whipple (1950-51), according to which the nucleus is a solid body (a few kilometers across) made up of various ices (frozen water, methane, ammonia, carbon dioxide, and hydrogen cyanide) in which dust is embedded. Dust particles are liberated when the ices vaporize as the comet approaches the Sun, and they get blown away by solar radiation pressure, often forming impressive, gently curved dust tails.
Dirty snowball model