Comets are not made of ices. The "Deep Impact" mission showed this beyond doubt. Hydroxyl (not water) emissions were approximately one percent of the debris from the "impact" event, which was much more energetic than impact models alone suggested. The electric force is responsible for ripping comets apart, just as it's responsible for cometary jets. Comets are rocks, they are not fragile, what's fragile is the Astronomy Picture of the Day's explanation that comets are fragile icy balls of dirt.
Read more at antwrp.gsfc.nasa.gov/ap...
