When it comes to 22-million-ton asteroids, the small stuff, it turns out, can make a huge difference in a potentially disastrous path toward Earth. Using limited observations and lots of high-end computer modeling, astronomers have gotten a better handle on the limitations of asteroid-track forecasting in a new study of a potentially threatening asteroid called Apophis. In this high-stakes game of Whack-a-Cosmic-Mole, just knowing exactly what it is you don't know can be useful. Apophis' chance of hitting our planet in 2029 is now slim to none, but astronomers will have to wait four to six years before they can...