http://www.usatoday.com/news/science/2003-12-02-asteroids-usat_x.htm
Small near-Earth asteroids pose more imminent threat By Dan Vergano USA TODAY December 2, 2003 Bad things can come in little packages, astronomers warn. So after a decade of searching for massive asteroids, they are turning to the threat posed by smaller, more common space rocks closer to Earth. Most worries about impacts from space have centered on objects more than half a mile across. They are thought to smack into Earth every few million years, some with such force they trigger mass extinctions like the one that ended the age of the dinosaurs 65 million years ago. But a recently released NASA "Near-Earth Object Search" report scheduled for discussion at the American Geophysical Union meeting next week calls for better observation of smaller asteroids. These rocks wouldn't trigger the global devastation of their larger brethren, but their impacts could still cause massive local damage, chiefly from tidal waves. Because asteroids about one-twelfth of a mile across hit about once every 1,000 years, they are a more imminent threat than giant impacts, the report warns. It was written by a team of scientists headed by space-surveillance expert Grant Stokes of MIT's Lincoln Laboratory. Asteroids come and go by Earth. In August, one nearly three-quarters of a mile wide named QQ47 received considerable media attention because of reports that it might hit Earth in 2014. But like many asteroid scares in recent years, astronomers quickly dismissed any impact possibility after more observation. But sometimes impacts happen. Most recently, an asteroid perhaps 200 feet wide blasted the Tunguska region of Siberia in 1908, flattening almost 800 square miles of forest. Five years ago, NASA began looking for larger asteroids and comets, hoping to detect 90% of them by 2009. About 60% of the estimated 1,200 large objects traveling near Earth have already been discovered. Among smaller asteroids nearby, perhaps half a million are "potentially hazardous," the report says. It suggests: * Tidal wave deaths from an ocean impact would be lower than past predictions, a few hundred people perhaps, because evacuations should lessen the risk. * Searches for small comets should be bypassed, because they represent only 1% of the impact risk. * A seven- to 20-year search for nearby small asteroids that pose about 90% of the impact risk would cost under $400 million. A mixture of ground telescopes and space probes would fit the criteria for the search recommended by the report. A satellite trailing near Venus to watch for sun-grazing asteroids combined with ground-based telescopes offers a quicker, but slightly more expensive, approach than relying on an Earth-orbiting telescope for asteroid warnings. ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
