A pale white person or object, with a mental handicap. first used to describe: "The Moon" from the famous radio/television series The Mighty Boosh. Therefor most apt when used as an adjective to describe satellites with gypsum like properties, but has rapidly found it's way into common usage in the English language.
Tony Harrison: " I took a chance, how was I to know he was an alabaster retard"
What one may call someone who is particularly white and stupid for instance the moon when asked for directions - originated from BBC 3 comedy The Mighty Boosh
Ok i took a chance, how was i supposed to know he was an Alabaster Retard