It's a classic science fiction scenario: An enormous asteroid is discovered hurtling toward Earth that is sure to trigger a cataclysmic extinction upon impact. Intrepid scientists have only a year to launch a preemptive strike against the space rock — to knock it off course or blow it to bits — with the fate of humankind at stake. Can they stop it?
This doomsday scenario is, in all likelihood, one humans alive today will never have to face. Astronomers have mapped the trajectories of more than 33,000 asteroids that make occasional close approaches to Earth, and none pose any risk of impact for at least the next 100 years.
