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An asteroid the size of an office building will zoom close by Earth next week, but it's not on a collision course, NASA says.
Still, some people think this near-miss should serve as a wake-up call.
"It's a warning shot across our bow that we are flying around the solar system in a shooting gallery," says Ed Lu, a former astronaut and head of the B612 Foundation, a nonprofit dedicated to protecting humanity from asteroids.
The asteroid known as 2012 DA14 was first spotted last year by astronomers in Spain. It's thought to be about 150 feet across and made of rock.
It will whiz past Earth on Feb. 15, going about 5 miles per second. At its closest approach, it will be only about 17,200 miles above the surface of our planet. That's far nearer to us than the moon, and even closer than some weather and communications satellites.
NASA officials say this event is one for the record books — the first time scientists have been able to predict something so big coming so close.
"There really hasn't been a close approach that we know about for an object of this size," says Donald Yeomans, manager of the Near Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
It will come closer than satellites in a geosynchronous orbit around 22,000 miles up, but is extremely unlikely to hit any of those as it goes by.
"This asteroid seems to be passing in the sweet spot between the GPS satellites and the communications and weather satellites," Yeomans says.
There really hasn't been a close approach that we know about for an object of this size.Donald Yeomans, NASA
Its flight path is well-understood enough to know that there's no chance it will hit the Earth.
That's a good thing, because if an asteroid this size did smack our planet, it could cause a huge amount of destruction — the equivalent of 2.4 million tons of TNT, Yeomans says. Such an impact would be comparable to the famous "Tunguska event" of 1908, when a space object of a similar size collided with Earth over Siberia and leveled millions of trees in an area of more than 820 square miles.
That kind of impact is only expected to happen once every 1,200 years or so, Yeomans says. But next week's close flyby shows that the threat from asteroids is real and can't be ignored, Lu says.
"The fact that this was only discovered a year ago highlights the problem," says Lu, who points out that if this particular asteroid had been headed straight for us, there'd be no time to do something like send up a spacecraft to try to nudge it off course.
"There's no way we could have stopped this. Nothing we could have done," Lu says. "The only thing we could have done, if this was going to hit us, was to evacuate the area."
Our planet orbits the sun in a swarm of space rocks, Lu says, and though NASA does surveys looking for the biggest ones, most of the asteroids out there haven't been discovered.
"We only know the locations and trajectories of about 1 percent of asteroids this size or larger," Lu says. "So for every one of these, there's 99 out there we don't know about."
That's why his group is working to build and launch a private space telescope that would search for asteroids, and find them before they find us.
An official at NASA headquarters said the agency is continually looking for ways to improve its ability to spot smaller asteroids — within the constraints of its budget.