1 -- The pictures taken by the Impactor on Tempel 1 approach showed a rocky surface, with the occasional white blob of something on it. Eventually, wouldn't all surface ices sublimate away, so that only a rock surface with no visible ice deposits would be seen?

2 -- Once #1 happens, the core ice deposits are now more insulated. Doesn't htat mean that less and less water (and attendant dust-in-solution) gets emitted as a visible tail?

3 -- Eventually, all the water/ice/non-rocky content will have blown off, leaving just this big rock sailing across the Universe. At this point, what do you call this thing? It would have no tail, so by definition (?) you couldn't call it a comet any more...at what point does a comet stop being a comet, and become an asteroid (or sumpin else) with an extremely elliptical orbit?

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1. The white blobs, something similar was seen on Wild 2 when Stardust flew past. The belief then was that they were areas of out gasing, geysers possibly. In the Temple 1 images I've noticed that the white areas seem to line up with what appear to be faults or fractures in the comet. So it could be possible that what we're seeing is ices erupting from somewhere below the surface.

2. Yes, but as the comet nears the sun and heats up, the most volitile ice sublimates first and finds it's way to the surface through the fractures and a big hole that a wayward spacecrft punched into the comet.

3. Once all the ice is gone it would be an asteroid.

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Thankee, Super...

...hmmm...

I wonder how many of the asteroids we treck today (Ceres, etc) started out life as comets?

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"If a tree is cut down in the rainforest, and is used to make paper to print a book, and the book is really bad, and there's nobody that will read it, do you still hear a sucking sound?"
Charlie in Dayton, A.AsC.

Probably alot of them, especially the ones in highly elliptical orbits.

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I'm not a scientist, but I play one on the internet.
http://www.rrac.org

Could we call it an asteroid or would we call it a bunch of meteoroids flying in very close formation? Presumably most rocky material in a comet isn't in the form of a huge boulder, but a bunch of gravel and sand. Or am I getting it wrong?

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I think we've had this discussion before about when is it a meteoroid, an asteroid or a planet. It's a continuum, I don't think anyone has designated the cut off size of each.

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I don't think that those areas are so much "white" as merely over exposed. The surface of a comet is very dark. To get any detail in the darkest areas, you wind up over exposing the lighter areas.

The dark surface is very good at absorbing heat from the Sun and transfering it to the volitiles deeper inside. These volitiles sublimate and seep out or often blow out of the interior.

It won't be a solid rock, but more of a gravel pile held together by it's own gravity. The asteroid Phaeton is thought to be such a remnant of a burned out comet.

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As a matter of fact, many asteroids are believed to be rubble piles. Most asteroids that have known satellites are much less dense than they should be if their composition is what is measured. Of course, the events that created those satellites may have disturbed the asteroids so we may have biased data.

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(1) AFAIK there is nothing that says that the surface was "a rocky surface". It certainly was mostly smooth (at a resolution of dozens of meters) but is/was still probably ices. The quick interpretation of the impact event suggests a top layer of very loose material with a deeper much more solid layer.