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In a frame grab made from a video shot with a dashboard camera a meteor streaks through the sky over Chelyabinsk, about 1500 kilometers (930 miles) east of Moscow, Friday, Feb. 15, 2013. A meteor that scientists estimate weighed 10 tons (11 tons) streaked at supersonic speed over Russia's Ural Mountains on Friday, setting off blasts that injured some 500 people and frightened countless more. (AP Photo/AP Video)The Associated Press

When the sky is falling, you can count on Richard Binzel to get excited.

Standing in his office at the Massachusetts Institute of Technology, Dr. Binzel brandishes a blackened lump of iron that is not of this Earth: "You wouldn't want to have this land on your head," he says.

Dr. Binzel's specialty is asteroids – the flying bits of rock and metal that whiz by our planet with disconcerting regularity and sometimes score a direct hit. The grapefruit-sized fragment in his hand is a piece of cosmic shrapnel from a massive iron meteorite that blazed over the Sikhote-Alin region of eastern Siberia in 1947.

Now, he and his fellow planetary scientists are abuzz over another Russian fireball, which exploded on Friday morning over Chelyabink, a city of more than one million people east of the Ural mountains. The blast wave created by a 15-metre space rock hitting the atmosphere at 18 kilometres per second broke windows and caused light structural damage. Estimates based on multiple sources of evidence, including infrasound – pressure waves at too low a frequency for humans to perceive – suggest the energy delivered was greater than would come from the detonation of about 470 kilotonnes of TNT.

"An impact of this size happens maybe once every 50 to 100 years," says Peter Brown, a meteor expert at the University of Western Ontario in London, Ont.

The unforeseen event came just as the world was getting ready to witness the close pass of a 50-metre asteroid known as 2012 DA14. Although unrelated, the near miss and the surprise hit focused global attention on the ever-present threat of asteroid impacts.

"It's a wake-up call," says Christopher Herd, an associate professor in the department of Earth and Atmospheric Sciences at the University of Alberta.

Dr. Herd is a member of the international committee that will name the Chelyabinsk fireball, a designation that will go with any pieces that turn up. Fragments would hold a special place in history, he notes, because they'd be chips off the largest meteorite ever observed on its flight through the atmosphere. Time is of the essence, he adds, because rare isotopes formed in the vacuum of space could be lost or contaminated by exposure to the elements.

"Getting samples into laboratories quickly will be key," Dr. Herd says.

If pieces of the fireball are found, scientists will be curious to see how much diversity they exhibit. Most meteorites are too small to be more than a single kind of rock, but a 7,000-tonne object that is 15 metres across is like a world unto itself. In 2008, a boulder-sized object that fragmented over Sudan contained several kinds of meteorites.

Whatever the scientific return, Friday's fireball was so spectacular and so well documented that it will invariably become a kind of Hurricane Sandy for asteroid surveillance – exhibit A in the argument for investing more resources in spotting objects of similar size so that people can be warned if an impact is imminent.

Prof. Brown says, in different circumstances, the object in Russia might have been spotted ahead of time by existing surveys, just as the Sudanese meteorite was. Initial indications are it approached Earth from the daylit side, which would have made it impossible to spot with a telescope on the ground. Prof. Brown adds it would require a significant increase in resources to detect most objects of equivalent size.

Some efforts are under way to beef up surveillance from space, including a small Canadian satellite, NEOSSat, due to launch on Feb. 25.

But Russell "Rusty" Schweickart, a former Apollo astronaut and advocate for asteroid surveillance, laments the lack of an internationally co-ordinated effort to spot larger threats. He is co-founderof B612, a non-profit group that wants to launch an infrared telescope called Sentinet that will travel on solar orbit to survey the larger asteroids of the inner solar system. It would track asteroids 30 metres wide or larger.

"We're looking at things that are going to involve potentially the deaths of many people, large destruction, not things that just break windows," he says.

"Once you find them and track them, then you can forecast decades ahead and thereby prevent their impact by deflecting them. That's why you need to begin these surveys as soon as possible."

Dr. Binzel expects that public awareness of asteroids received a big boost on Friday. He is involved in NASA's OSIRIS-REx mission, due to launch in 2016, which aims to rendezvous with and retrieve a sample from a near-Earth asteroid. Such missions will help characterize passing objects and better ascertain the threat.

"They've always been there, they always will be there," says Dr. Binzel. But now we're paying attention," he says.

-With a report from Tu Thanh Ha

A timeline of the meteor

The entry: A 7,000 tonne meteor entered the atmosphere above Chelyabinsk, Russia, at 9:20 a.m. local time at a speed at least 54,000 kilometres an hour, disintegrating at a height of 30 to 50 kilometres. Researchers at NASA say it hailed from the asteroid belt between Mars and Jupiter.

The strike: The meteor unleashed a force 20 times more powerful than the Hiroshima bomb, although the space rock exploded at a much higher altitude. The fireball it produced was dramatic, causing a sizable sonic boom.

The fallout: An estimated 1,000 people including 200 children were injured. Many were hurt rushing to windows to glimpse the fireball, only to have the windows shatter seconds later. Shock waves from the debris are believed to have knocked in part of the roof and walls of a local zinc plant and damaged 3,000 other buildings.

-Associated Press

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