[Windflier]

Comets consist of heavy water. Icy asteroids are more like regular H2O.

Um....maybe not. The last couple of missions to comets discovered them to be solid rock.

http://www.freerepublic.com/focus/chat/3704759/posts?page=24#24

[Vaquero]

Yeah once past the sun a few dozen times all the ice will have sublimated