An Etymological Dictionary of Astronomy and Astrophysics

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.

See also: → dirty; → ice; → ball; → model.