re: Good survey of Deep Impact info
Was reading Astronomy mags while on vacation and came across an article that says comets might not be as pristine as thought because of radiation penetration up to a few yards. With this talcum like powder surface it isn't hard to imagine.
But is the heat from inside a comet and passing by the sun evaporating it away?
The dirty ice/rock comet talk seems right with dark observations of Borelly and other comets. Can radiation exposure create the dark ares?
Hopefully Stardust will give us some insight.
Credit: Univ. Maryland, JPL-Caltech, NASA