[Cross posting this to the three threads where it's being discussed]
Having intimate knowledge of the DI spacecraft and mission:
The purpose of the mission has nothing to do with "blowing it up", "knocking it off course" or anything of the like. The purpose is to examine for the first time the composition of cometary material, primarily original core material shielded by billions of years of melting and refreezing.
The DI Impactor will create a large crater in Tempel 1, while the Flyby will examine the ejected material with an array of optical sensors.
While the media has focused on several comments made early in the program to the effect that since we really don't know the density of a comet, DI *could* conceivably break it apart, most scientists working this issue are convinced that the impact will create a significant crater but nothing more.
I found most amusing the quote from the article "But Russian astrologist Marina Bai gave it a try, and, according to her lawyer Alexander Molokhov, it looks like she may just pull it off."
I don't know who's crazier, she or her lawyer.