Most asteroids sit peacefully in the asteroid belt between Mars and Jupiter. Occasionally, some get kicked out due to tidal or gravitational forces between space objects, giving them their own orbit around the sun. Some of the stray asteroids pass fairly close to earth, and when they do we call them near earth asteroids.
2005 YU55 imaged with the Arecibo radio telescope
You may have heard talk on the news of a near earth asteroid called 2005 YU55 (pictured above). There's been a bit of hype about this object lately, but its just another member of the group of 8500+ near Earth objects that pass safely by Earth all the time. Now, "near" in the case of 2005 YU55 means that it will be 202,000 miles away from earth at its closest approach on November 8th, 2011. That's just a little bit closer than the moon is to Earth. So don't be alarmed by the news stories entitled "huge asteroid headed for close encounter with Earth"; there's nothing to worry about! NASA has assigned it a risk of 0 on their danger scale (ie. it's no big deal!)
Image credit: NASA/JPL-Caltech
