Summary: Like a sort of homeworld security force, teams of astronomers are keeping their eyes on the sky for potential deadly invaders from space. They’ve already found most of the really dangerous ones, and now they’re looking for those that are the next threat-level down. The potential invaders are asteroids with orbits that come close to Earth’s orbit around the Sun. These giant boulders could someday hit Earth, causing widespread damage. In the 1990s, Congress instructed NASA to find and plot the orbits of at least 90 percent of all the near-Earth asteroids that are one kilometer in diameter or larger — large enough to cause global damage if they hit us. And the search teams that NASA’s funded think they’ve done just that. They’ve found hundreds of objects in that category, but none on a likely collision course. Now, the search has been expanded to asteroids that are as small as 140 meters in diameter — about 450 feet. That’s big enough to cause major regional damage, but not global. Just last year, searchers found an asteroid of about that size that could hit Earth in 2040. The odds are small, but the possibility can’t be ruled out. Astronomers will look for the asteroid again next year. New measurements of its position will allow them to plot a more accurate orbit — and let us know whether our home planet could face the risk of a deadly invasion in the decades ahead. We’ll talk about a mission to a Near-Earth Asteroid tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.
