NASA's 5-step plan for when it discovers a giant, killer asteroid headed straight for Earth

If a giant asteroid were to hit the Earth, NASA and FEMA have a plan. Although an astroid of that size would be rare — NASA estimates a one-mile-wide astroid only hits the Earth once every million years — the two agencies have performed multiple test runs to ensure we'd be prepared. "It's not a matter of if, but when, we will deal with such a situation," said astrophysicist Thomas Zurbuchen.