FEYERICK: It is half the size of a football field and it is hurtling to earth at 17,000 miles an hour. The asteroid is expected to pass inside satellites orbiting our planet. And if that's too close for comfort, well, you're not alone. Tom Foreman gives us a look at the close encounter to come.</s>TOM FOREMAN, CNN CORRESPONDENT: In cosmic terms, this is a very close encounter, the closest one that NASA has ever seen for something this big. Let's get some reference points here. When we talk about the earth, many of us like to think the moon is close to us, but it's really not as close as you think. It's almost a quart million miles away. So what is close in space, satellites. We've been launching these for many decades now and we fill the sky with them. Some are fairly low, others are quite high. The highest out there are communications and GPS satellites about 22,000 miles up in the air. So where is this asteroid going to be? It is going to shoot out of the sky and cut right through the top of the satellite belt at about 17,000 miles. Is that dangerous? No, not really, in part because of the size of this thing, the official name, by the way, is 2012 DA14. It's only about 50 yards long or wide. It will be traveling 18,000 miles an hour almost. That's fast. If it were to hit earth it would have a huge explosion equal to more than 2 million tons of dynamite. But that really wouldn't be enough to harm the earth unless it hit a populated place. Yes, it would knock down trees and destroy an area of several hundred miles but that would be all. Most importantly, scientists who have been tracking this thing for more than 2 million miles already say it's just not going to hit the earth. It is going to miss even though this is a very close call.
Asteroid Hurtling Closer To Earth