Huge asteroid is expected to whiz by Earth next week.
An asteroid 150 feet wide will come closer to Earth than any other known asteroid of its size.
But NASA says we don't have to worry.
Asteroid 2012DA14 will pass by Earth next Friday at 17,400 mph.
It'll pass 17,200 miles over our rooftops - five thousand miles closer than satellites we use every day for television and other communications.
Astronomers first spotted the asteroid a year ago as a tiny dot in a star field. Since then, they've tracked it carefully and measured its exact size, leading them to this reassuring conclusion:
"It cannot hit earth," said Don Yeomans, with NASA.
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