Scheduled for July 4th, the Deep Impact mission will be sending an impact probe on a crash course with a comet half the size of Manhattan. The parent craft will record all the metrics of the impact from 310 miles away.
"In the world of science, this is the astronomical equivalent of a 767 airliner running into a mosquito," said Don Yeomans, a Deep Impact mission scientist at JPL. "The impact simply will not appreciably modify the comet's orbital path. Comet Tempel 1 poses no threat to the Earth now or in the foreseeable future."