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Asteroids and comets: Every year, millions of these 'stray bullets' streak the skies, and tons of small meteorites strike our planet! Some 65 million years ago, dinosaurs were wiped off the face of the earth in what many believe was the aftermath of a massive comet collision. Could something like this happen again? Scientists believe that the impact of an asteroid only a mile wide would be globally catastrophic. Join extraordinary geologist Eugene Shoemaker and his wife Carolyn who have remapped the heavens with their discoveries of more than 30 comets and hundreds of asteroids. Now that we know what's out there, how can we defend ourselves?