Message #194039

[Atrion]

 DEEP IMPACT: Asteroids and comets have routinely collided with Earth since our planet was formed four billion years ago, although these are rarely catastrophic, because most aren't large enough. The total mass of all the asteroids combined is less than that of the Moon. But occasionally a very large asteroid -- a quarter mile wide or more -- will strike with devastating effects, such as the extinction of the dinosaurs. When an asteroid, or part of it, crashes into Earth, it is called a meteorite. There are currently two programs in the US to actively search for these near-earth objects: NASA's Near Earth Asteroid Tracking program and Spacewatch at the University of Arizona.

The American Astronomical Society  contributed to the information contained in the video portion of this report.

http://www.sciencedaily.com/videos/2007/0608-visit_to_an_asteroid.htm