re: A stationary BB would alter its orbit
In about 20 years Comet Tempel 1 will make a close pass at Jupiter, which will alter its orbit by 20 million miles. Jupiter is the biggest comet influencer in the Sol system, at least until we improve our space infrastructure and start mining comets for fuel.
As others have said, and Russian astrologers aside, Deep Impact hitting the 9-mile-long comet is like a mosquito hitting a 767.