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5:23 am
Thu November 7, 2013

To Understand A Russian Fireball, Physicists Turn To YouTube

Originally published on Thu November 7, 2013 1:26 pm

Nine months ago a 12,000-ton meteor exploded over Chelyabinsk, a Russian city with 1.1 million residents. Hundreds of personal videos captured the fireball's flight — and that means you can watch the spectacle from almost any vantage point on YouTube.

Now, in large part by poring over these videos, physicists have been able to estimate the power of that explosion, calculate the exact trajectory of the meteor and figure out why we didn't see it coming.

It all started with a small asteroid — one of the millions of unremarkable gray rocks circling the sun. But this particular asteroid was exceptionally unlucky. Shortly after the sun rose over central Russia on Feb. 15, the asteroid collided with the Earth's atmosphere and became a fiery meteor.

Eleven hours later, as the sun rose over Ontario, physicist Peter Brown turned on the television and heard the news.

"I was almost in shock for the first 24 to 48 hours," says Brown, a professor at Western University in London, Ontario. "You know the odds of this happening were so incredibly low, for me to see it in my lifetime, during my career — it's negligible."

The event was especially exciting for Brown, because he studies how meteors explode. But instead of hurrying to YouTube to watch more videos of the meteor, he pulled up some fresh data from a completely different source: the Comprehensive Nuclear-Test-Ban Treaty Organization.

The CTBTO maintains a global network of sensors to make sure no one is blowing up nukes. They look for radioactive isotopes, seismic shocks and super-low-frequency sound waves. Seventeen of their sensors picked up a striking low-frequency rumble on Feb. 15.

Those readings confirmed what Brown suspected — this was the largest so-called "airburst" in more than a century. It was 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 the citizens of Chelyabinsk, but an amazing opportunity for researchers.

"You can think of it as Christmas in meteor-astronomy land," Brown says. "Now we have this event that can answer questions we've been posing for years."

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 created by trees knocked down 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 published two papers based on this data in this week's issue of the journal Nature.

They analyzed videos from dash cams — video cameras widely installed by wary Russians over the last several years as a defense against insurance fraud and police corruption. The viewpoints from all those cameras allowed the scientists to triangulate the meteor's exact trajectory. They were also able to figure out the meteor's diameter (about 65 feet), its entry speed (around 42,000 mph) and the answer to a pressing question: Why didn't we see it coming?

"The answer is — it came right out of the sun," Brown says.

Like a new moon, the asteroid was illuminated from behind, so it was nearly invisible.

Researchers also have a possible lead on the meteor's origin. A known asteroid more than a mile-wide has a nearly identical orbit. So it's possible the Chelyabinsk meteor is a chip that broke away from this larger rock.

While studying this latest event, scientists reviewed similar impacts from the past few decades and discovered something odd. The rate of these impacts is an order of magnitude higher than previously thought — higher than surveys of all the rocks floating around in the solar system would suggest.

It's a bit unnerving. But Brown says studying the Chelyabinsk impact will help scientists prepare people for future impacts by more accurately predicting potential damage.

"You can pass that information to appropriate national authorities," Brown says. Such research could help public officials answer key questions, he says, such as, "Should you just be warning people to stay away from windows or should you be evacuating the city?"

We could someday have a meteor warning system — just like the ones we have for hurricanes and tornadoes.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

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. Transcript provided by NPR, Copyright NPR.