November 6, 2013

Studies warn about space rock threat

The meteorite that hit over Russia indicates collisions are up to five times as likely as originally thought.

By Seth Borenstein
The Associated Press

WASHINGTON — Scientists studying the terrifying meteor that exploded over a Russian city last winter say the threat of space rocks smashing into Earth is bigger than they thought.

click image to enlarge

In this screen image made from a dashboard camera video shows a meteor streaking through the sky over Chelyabinsk, about 930 miles east of Moscow on Feb. 15, 2013. The meteor hit Earth at 42,000 mph and exploded over the Russian city, smashing windows and causing minor injuries.

The Associated Press

click image to enlarge

This photo provided by The Field Museum in Chicago shows pieces of the meteor that exploded over Russia’s Ural Mountains in February after they were catalogued on their arrival at the museum. The museum received nearly two pounds of small meteorite pieces donated by a collector.

The Associated Press

Meteors about the size of the one that streaked through the sky at 42,000 mph and burst over Chelyabinsk in February — and ones even larger and more dangerous — are probably four to five times more likely to hit the planet than scientists believed before the fireball, according to three studies published Wednesday in the journals Nature and Science.

Until Chelyabinsk, NASA had looked only for space rocks about 100 feet wide and bigger, figuring there was little danger below that.

This meteor was only 62 feet across but burst with the force of about 40 Hiroshima-type atom bombs, scientists say. It released a shock wave that shattered thousands of windows and injured more than 1,600 people, and its flash was bright enough to temporarily blind 70 people and cause dozens of skin-peeling sunburns just after dawn in icy Russia.

Up until then, scientists had figured a meteor causing an airburst like the one in Russia was a once-in-150-years event, based on how many space rocks have been identified in orbit. But one of the studies now says it is likely to happen once every 30 years or so, based on how often these things are actually hitting.

Scientists said a 1908 giant blast over Siberia, a 1963 airborne explosion off the coast of South Africa, and others were of the type that is supposed to happen less than once a century, or in the case of Siberia, once every 8,000 years, yet they all occurred in a 105-year timespan.

Because more than two-thirds of Earth is covered with water and other vast expanses are uninhabited deserts and ice, other past fireballs could have gone unnoticed.

Lindley Johnson, manager of NASA’s Near Earth Object program, told The Associated Press that the space agency is reassessing what size space rocks to look for and how often they are likely to hit.

By readjusting for how often these rocks strike and how even small ones can be a threat, “those two things together can increase the risk by an order of magnitude,” said Mark Boslough, a Sandia National Lab physicist, co-author of one of the studies.

In fact, the U.S. government got a new sense of urgency after Chelyabinsk, quietly holding a disaster drill earlier this year in Washington that was meant to simulate what would happen if a slightly bigger space rock threatened the East Coast.

In the early part of the drill, when it looked as if the meteor would hit just outside the nation’s capital, experts predicted 78,000 people could die. But when the mock meteor ended up in the ocean, the fake damage featured a 49-foot tsunami and shortages of supplies along the East Coast, according to an after-action report obtained by the AP.

The exercise and the studies show there’s a risk from smaller space rocks that strike before they are detected — not just from the long-seen-in-advance, dinosaur-killing giant ones like in the movie “Armageddon,” said Bill Ailor, a space debris expert at the Aerospace Corporation who helped coordinate the drill.

“The biggest hazard from asteroids right now is the city-busting airbursts, not the civilization-busting impacts from 1-kilometer-diameter objects that has so far been the target of most astronomical surveys,” Purdue University astronomer Jay Melosh, who wasn’t part of the studies, wrote in an email. “Old-fashioned civil defense, not Bruce Willis and his atom bombs, might be the best insurance against hazards of this kind.”

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