The problem with quoting asteroid impact statistics is that they can sound cold, unsympathetic and irrelevant to our daily lives. Friday's historic meteor airburst over the Russian city of Chelyabinsk, however, gave the statistics of being hit by space rocks a very human twist.
Today, the European Space Agency (ESA) updated their assessment of the meteor that generated a huge shock wave, injuring nearly 1,500 people and causing damage to thousands of buildings on Feb. 15. After reviewing the many eyewitness videos, analyzing data from infrasound stations and surveying the region affected, ESA scientists think the airburst was a one in "several of tens to 100 years"-type of event. In other words, on average, we can expect something of this scale to happen a little more than once a century.
But this "once in a century" happened last week over a city inhabited by a million people.
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The Chelyabinsk airburst is the largest known impact event since the River Curuçá impact (in 1930) and the Tunguska impact (in 1908), the latter of which was an airburst event caused by an asteroid or comet fragment slamming into the upper atmosphere, blasting a powerful shock wave onto a remote forested region. 80 million trees were flattened over an area of 2,150 square kilometers (830 square miles) - the approximate area of Moscow. The Chelyabinsk event was a scaled-down taster of what happened over Tunguska, some 1,800 kilometers (1,100 miles) to the northeast of the same country over a century ago.
It is now clear that the Chelyabinsk-bound space rock had a mass of up to 10,000 tons and a diameter of around 15 meters (50 feet) before it slammed into the atmosphere at a shallow angle - around 20 degrees. The meteoroid was traveling at 18 kilometers (11 miles) per second - that's a whopping 64,000 kilometers (40,000 miles) per hour. NASA scientists are now have an idea about the impactor's characteristics and they have been able to trace its approximate orbital trajectory around the sun.
But no impact would be complete without calculating its destructive power. Judging by the energy inferred by infrasound stations, scientists reckon the meteor delivered the equivalent energy of 500 kilotons of TNT detonating at the same time. That's roughly 30 Hiroshima-size nuclear bombs exploding 15-20 kilometers (9-12 miles) above the Earth's surface. (As a comparison, the Tunguska event unleashed around 30 megatons of TNT equivalent energy - around 1,000 Hiroshima bombs.) So when eyewitnesses saw the stunning contrail overhead, it took a couple of minutes for the shock wave to impact the ground, causing widespread damage.
Windows were blown out, buildings suffered structural damage and hundreds of people were hurt, dozens remain in hospital days after impact. 24,000 emergency personnel have been dispatched to the region to inspect the infrastructure for damage. In total, it has been estimated that the city sustained 1 billion rubles ($33 million) worth of damage.
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The secondary impacts of this event are also clear. At time of the morning impact (around 9:20 am local time) the air temperature was -15 degrees Celsius (5 degrees Fahrenheit), so exposure to low temperatures were of immediate concern, particularly to vulnerable citizens such as the elderly and sick.
Be under no illusion, the people of Chelyabinsk and the surrounding area sustained a cosmic flesh wound. Although the damage was extensive and a number of people sustained serious injury, if this type of event were to happen over New York, Tokyo or London, say, the economic fallout - let alone the inevitably larger human toll - could be crippling.
The chances of Earth getting hit by an asteroid in the near future are slim; the chances of a specific populated region suffering the fallout of such an unlikely event are vanishingly small. But those statistics matter little to the people of Chelyabinsk. In this game of cosmic Russian roulette, the ball of chance landed on their number and they got hit - the first modern city to have succumbed to an impact event.
One group of astronomers will be feeling especially vindicated right now; asteroid hunters who have, for years, been watching the skies for marauding chunks of rock and metal in our solar system, warning us that this will happen. Like the people of Chelyabinsk, they realize the odds of a city getting struck by a meteor shock wave or meteorite impact are low. But it will happen in the future - like it happened in the very recent past - we just don't know where or when.
"Wouldn't it be silly if we got wiped out because we weren't looking?" Edward Lu, former NASA astronaut and CEO of the B612 Foundation, told the New York Times on Saturday. "This is a wake-up call from space. We've got to pay attention to what's out there."
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The vast majority of extinction-level asteroids are being tracked and aren't going to bother us any time soon, but there are millions of undetected space rocks the size of the Russian meteor (and bigger), some of which will hit us. They shouldn't invoke panic, but they should invoke concern. Wouldn't it be a good idea to better fund asteroid detection programs so we can detect smaller space rocks before they hit? Ultimately, wouldn't it be prudent to learn more about asteroid composition and asteroid deflection strategies? Fortunately we have the technology to do all of these things, but it takes social and political will to get them funded.
Will the Chelyabinsk event be a powerful enough wake-up call to global policymakers? We now have a vivid account of what it's like to have an average morning commute violently transformed by the unsympathetic cosmos. The sky may not be falling, but, occasionally, rocks do.
Humans are so intelligent and powerful... until a rock drops out of the sky.
Image: Morning commute, interrupted. Credit: Youtube