Hope they don't knock it into the earth.
On July 4, the Deep Impact mission will smash a probe into Tempel 1, a potato-shaped comet discovered in 1867 and believed to be representative of most comets. The impact will carve out a stadium-sized crater and provide valuable information about a comet's interior.
http://www.cnn.com/2005/TECH/space/06/07/deep.impact/index.html