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RENEE MONTAGNE, HOST:

This is MORNING EDITION from NPR News. I'm Renee Montagne.

DAVID GREENE, HOST:

And I'm David Greene. Earlier this year, a 12,000 ton meteor exploded over Russia.

(SOUNDBITE OF EXPLOSION)

GREENE: Now, meteors don't buzz us every day so you might wonder why someone was recording that audio. Well, the explosion happened near Chelyabinsk, a city with more than a million people and plenty of drivers. And many Russian drivers keep dashboard cameras rolling all the time. They can be a way to prove to police what actually happened in an accident.

Dashboard cams and cell phones captured video of the fireball's flight and a lot of it's on YouTube. As NPR's Adam Cole reports, it's given scientists a way to figure out where that meteor came from and why we didn't see it coming.

ADAM COLE, BYLINE: The meteor started out as a small asteroid, one of the millions of unremarkable gray rocks circling the sun. But this particular asteroid had a cosmic traffic accident. Shortly after the sun rose over central Russia on February 15, this asteroid collided with the Earth's atmosphere and became a fiery meteor. And when the sun rose over Ontario 11 hours later, physicist Peter Brown turned on the television to hear this.

UNIDENTIFIED WOMAN: An extraordinary spectacle lit up a piece of Russia's sky this morning.

PETER BROWN: I was almost in shock really for the first 24 to 48 hours.

COLE: Brown is a professor at Western University in Ontario and he studies how meteors explode.

BROWN: You know, the odds of this happening were so incredibly low, for me to see it in my lifetime, during my career is negligible.

ADAM CO,LE, BYLINE: Brown could've gone to YouTube to watch more videos of the meteor, but instead he pulled up that morning's data from a completely different source, the Comprehensive Nuclear Test Ban Treaty Organization. The CTBTO maintains a global network of censors to make sure no one is blowing up nukes. They look for radioactive isotopes, seismic shocks and super low frequency soundwaves.

(SOUNDBITE OF SOUND WAVE)

COLE: That's what 17 of those sensors picked up on February 15, with the frequency adjusted so humans can hear it. The soundwaves confirmed what Brown suspected. This was the largest so-called air burst in over a century, 30 times more powerful than the bomb dropped on Hiroshima. It didn't cause as much damage because it exploded several miles up, but the blast still knocked people off their feet and broke windows, causing thousands of injuries.

It was a shock for citizens of Chelyabinsk, but an amazing opportunity for researchers.

BROWN: You could think of it as Christmas in meteor astronomy land. Now we have this event that's going to be able to answer all sorts of questions that we've been posing for years.

COLE: The last big meteor explosion happened back in 1908 over a remote corner of Siberia. To figure out its size and power, scientists had to examine the pattern of knocked down trees in the area. But this time scientists have way more data, not just from sensors and satellites but from all those uploaded YouTube videos. Brown and his colleagues from the Czech Republic have just published two papers based on this data in Nature magazine.

They analyzed videos from dashboard cams, video cameras installed by wary Russians as a defense against insurance fraud and police corruption. All those viewpoints allowed them to triangulate the meteor's exact trajectory. They also calculated the meteor's diameter.

BROWN: It was about 20 meters in size.

COLE: Its entry speed.

BROWN: Nineteen kilometers per second.

COLE: And the answer to a pressing question: Why didn't we see it coming?

BROWN: And the answer is, it came right out of the sun.

COLE: Which made it nearly invisible. When we do see a meteor coming, which is a whole other challenge, Brown says all the data from the Chelyabinsk impact will help scientists predict potential damage.

BROWN: And then you can pass along that information to appropriate national authorities. You know, should you just be warning people to stay away from windows or should you be evacuating the city?

COLE: A sort of meteor warning system, just like the ones we have for hurricanes and tornadoes. Adam Cole, NPR News.

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