In 1997 astronomer Jim Scotti discovered the asteroid 1997 XF11. Initial calculations predicted that the asteroid would make an extremely close approach to Earth in 2028. A collision would result in a global catastrophe, killing hundreds of millions of people. More accurate calculations of the orbit of the asteroid, however, determined that its probability of colliding with Earth is zero. Nonetheless, Hollywood films such as Deep Impact and Armageddon, both released in 1998, illustrated the global crisis that a comet or asteroid heading toward Earth would generate. Together with the alarming news about 1997 XF11, these movies heightened public awareness of the threat from an asteroid impact. As a result, the National Aeronautics and Space Administration (NASA) doubled its funding to $3 million a year for searching for near-Earth objects (NEOs). In addition, NASA initiated the Spaceguard Survey, intended to find 90 percent of all NEOs larger than 1 kilometer (0.62 mile) in diameter by 2008. Ultimately, the...