ROBERT SIEGEL, HOST:
This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel. An asteroid the size of an office building zipped past Earth this afternoon. It came closer to us than some weather and communication satellites are. But this much anticipated event was completely upstaged by a different space object that unexpectedly collided with our planet. NPR's Nell Greenfieldboyce reports that a meteor exploded over Russia, shattering windows and injuring hundreds of people.
NELL GREENFIELDBOYCE, BYLINE: Asteroids and meteors are essentially the same stuff. When a hunk of metal or rock is flying around out in space, it's called an asteroid. When it hits our atmosphere, it's a meteor.
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GREENFIELDBOYCE: Today, the big news was a meteor. In this Associated Press recording, you can hear breaking glass and car alarms after it exploded over Russia, creating damaging shock waves over a populated area. Videos show the fireball streaking across the sky.
PAUL CHODAS: Those who witnessed it would have seen an event that was brighter than the sun.
GREENFIELDBOYCE: Paul Chodas is with the Near-Earth Objects Program at NASA's Jet Propulsion Laboratory. He says space rocks the size of basketballs hit the Earth every day, but this kind of impact happens only once every 100 years or so.
CHODAS: It was indeed a large fireball, probably the largest fireball since the Tunguska event that hit Siberia in 1908.
GREENFIELDBOYCE: That one leveled trees over hundreds of square miles. Chodas says it's just a coincidence that this one also came down over Russia.
CHODAS: It's random where an asteroid might hit the Earth. Russia is a large area.
GREENFIELDBOYCE: So that means it's a big potential target. Scientists say it's also just a coincidence that this space rock hit just as sky watchers were getting ready for another rare event, the close approach of the asteroid called 2012 DA14. As expected, it harmlessly passed our planet, going by about 17,000 miles above Indonesia.
ALAN HARRIS: As far as we can tell, there's absolutely no connection between these two events, although it seems quite amazing.
GREENFIELDBOYCE: Alan Harris is an asteroid scientist at the German Aerospace Center in Berlin. He says 2012 DA14 was around 150 feet across, so scientists were able to spot it about a year ago and tracked its path. The one that came down over Russia was much smaller, probably only around 50 feet across.
HARRIS: And that is basically just so they're under the radar, if you like. It's just the sort of object that will pass through the net that we don't have a hope of detecting really with the sort of search programs we have.
GREENFIELDBOYCE: He says a couple of research groups have plans for specialized telescopes that could detect smaller asteroids like this one...
HARRIS: ...and could give us a two- or three-week warning period before something like this in Russia happen. And then in a worst-case scenario, you can imagine you have time enough to evacuate people from the point of impact.
GREENFIELDBOYCE: Harris was actually at the United Nations in Vienna today for a meeting of experts on how to detect and deal with potentially dangerous space rocks. Today's two unusual events gave them a lot to talk about. Nell Greenfieldboyce, NPR News.