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.
What would happen if it did hit? In 1900, an object just a little smaller exploded over Siberia.
It leveled more than 800 square miles of forest. A city would have been similarly flattened.
It'll be traveling nine times the speed of a rifle bullet -- actually, about the same speed as the International Space Station, which is also not in danger.
And its close approach is a valuable lesson: Asteroid impacts with Earth are not only a thing of the past. They are a thing of the present and future.