These observations supported a number of longstanding hypotheses about comet construction , particularly Fred Whipple 's `` dirty snowball '' model , which correctly predicted that Halley would be composed of a mixture of volatile ices -- such as water , carbon dioxide , and ammonia -- and dust .
These observations supported Fred Whipple 's `` dirty snowball '' model . This correctly predicted that Halley would be composed of a mixture of volatile ices -- such as water , carbon dioxide , ammonia , -- and dust .