ronaldo

http://www.space.com/scienceastronom..._020326-1.html

On March 8, a hunk of stone and metal about the size of an 18-story building, made its closest approach to Earth, passing roughly 298,400 miles (480,200 kilometers) from the planet, just a bit farther out than the Moon, but a little too close for comfort for most astronomers.

But what was most disturbing was that the asteroid, later named 2002 EM7, passed virtually unseen. Not until March 12, when it had moved out of the glare of the Sun and into the night sky was it seen from Earth.

And it was not alone: On Jan. 7, an asteroid the size of three football fields came within two lunar distances and was spotted only a month before. Last October, a smaller asteroid passed by at a similar distance and was detected just two days prior.

For each nearby asteroid that is spotted, several pass entirely unnoticed, some closer to us than the Moon, scientists say. One researcher estimates that each year, 25 asteroids roughly as large as 2002 EM7 whiz by at even closer distances.

They slip through because of limitations to technology, telescope time, and funding.

These close brushes illustrate a message that asteroid researchers have repeatedly tried to hammer home to politicians and the public: The number of undiscovered asteroids far exceeds the known list, and the list needs to be filled out before it's too late.

Asteroid 2002 EM7 left a a pretty ominous message on its own: Only a tremendously expensive new telescopes -- placed outside Earth's orbit so as to monitor the blind spot created by the Sun -- could guarantee we won't suffer an unexpected and sudden impact. There would be a flash of brilliant light in the sky, and seconds later the world would change forever in a way that would render Sept. 11 an insignificant memory.