Asteroids wreak global havoc only once every 100,000 years or so--contrary to what tabloid headlines might suggest. But planetary scientists have plenty of reasons to eyeball asteroids: Aside from keeping a vigil for wayward rocks headed our way, they probe cosmic chunks for carbon and water--the raw materials for life--and even for signs of life itself. And things in the asteroid belt keep getting more interesting: In today's Nature, astronomers report the second-ever discovery of a moon orbiting an asteroid (Science, 14 May, p. 1099).
To bone up on asteroids, try the Web site of NASA's Jet Propulsion Lab's Near-Earth Object Program, where you can learn about Potentially Hazardous Asteroids (PHAs): 192 supersized rocks at last count that come within 7.5 million km of Earth's orbit. The site links to news stories and offers images of asteroids and meteor showers, as well as info on spacecraft sent on asteroid rendezvous. For gritty technical details, experts can visit NEODyS, a database that generates a Web page of observational data on each PHA and its predicted orbit. One that researchers are keeping a particularly close eye on is 1998OX4, which could hit Earth between 2014 and 2046. Don't blow your life savings just yet: The probability is less than one in a million, and, even if it does hit, at 200 meters across, 1998OX4 is not big enough to inflict cataclysmic damage.