NASA is prepared to blast a spacecraft into an asteroid at 16,000 mph in an unprecedented attempt to sway it off track. However, the one-year mission, which will begin on Nov. 24, raises a fundamental conundrum for scientists and security experts: whose job is it to guard the world against a potentially life-ending piece of rock if one were to come our way? Right now, the answer is no one. A huge asteroid striking Earth is a “once in a millennium type of event,” according to NASA. Each year, the space agency uses modern telescopes and other stargazing methods to uncover thousands of previously unseen “near-Earth objects” with orbits that will someday bring them into our galactic neighborhood.