Re. the fate of comet tails.
http://www.space.com/scienceastronom...il_000405.html
Here's a small excerpt:-
Scientists say the Ulysses-Hyakutake collision will help comet experts understand the life cycle and fate of comets, which many think of as prehistoric relics from the earliest days of the solar system. In particular, the discovery of such a long comet tail invites astronomers to believe that they may find and study past comets whose tails are still intact.
"Nobody really believed that you could have a comet tail this long," said Gloeckler. "They thought it would break up, dissipate, and it would be so diluted, you wouldnt see it at all. But now with this kind of measurement, its clear that these tails stay intact far longer."