The meteor that exploded over Russia was much smaller than the asteroid that will buzz Earth Friday. But it shows how destructive Earth impacts can be ? and how unexpected.
A simulation of asteroid 2012 DA14 approaching from the south as it passes through the Earth-moon system on Friday. The 150-foot object will pass within 17,000 miles of the Earth.
JPL-Caltech/NASA/AP
EnlargeAs scientists prepared to watch a massive asteroid zip past Earth Friday, a?10-ton meteor lit up the sky over the Russian region of Chelyabinsk before exploding into fragments high above the ground. And just like that, a day of one flying space rock became a day of two.?
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"This is a big deal," says Kaliat Ramesh, a professor of mechanical engineering at Johns Hopkins University in Baltimore. "You really should view this meteoroid we saw in Russia as a wake-up call" regarding the hazards even small objects can present, he adds.
Indeed, it's a day of multiple wake-up calls.
At 2:24 p.m. EST today, asteroid 2012 DA14 passed within a scant 17,200 miles of?Earth ? a whisker in cosmic terms.
The asteroid is about 150 feet across and poses no threat to Earth, astronomers say, although an object of that size could take out a major metropolitan area if it collided with the planet. But the asteroid's close approach provides a unique opportunity for researchers to track and study it in ways that could improve their ability to distinguish truly hazardous asteroids in near-Earth orbits from the more benign objects.
Russia's meteor, however, has been anything but benign.
The first reports of the meteor came in a 7:55 a.m. local time, with many people capturing the event using video cameras installed in their cars.
The meteor, perhaps the size of a small cargo truck, was traveling at about 33,000 miles per hour. It exploded into fragments somewhere between 18 and 30 miles above the Earth. The shock wave from the blast ? heard in the central Russian cities of Chelyabinsk, Yekaterinburg, and Tyumen ? blew out windows at locations closest to the meteor's path. At least 950 people were injured, mostly from flying glass, according to the Moscow Times.
In addition, a zinc factory was damaged, and cell-phone service was knocked out in some areas.
Although the event occurred as asteroid 2012 DA14 was on its final approach to its close encounter with Earth, the different paths the two objects traveled make it unlikely the meteor was a 2012 DA14 cast-off.?
Astronomers will have a better sense of the meteor's final orbit once they study the video that's available from the event, says Gareth Williams, an astronomer and associate director of the International Astronomical Union's Minor Planet Center in Cambridge, Mass..
He explains that the video will allow researchers to reconstruct the meteor's path through the atmosphere in three dimensions. They can use this information to calculate the meteor's most probable orbit before its demise.
This was one of countless objects in near-Earth orbits that had eluded detection, despite efforts over the past 15 years to take a detailed census of these objects.?
The meteor "was not seen before it entered the atmosphere," Mr. Williams says. Had it been detected and reported to the center, it would have received a designator, similar to 2012 DA14, and we all could be describing this event as a collision with a small asteroid, he suggests.
Researchers say that objects the size of the Chelyabinsk meteor?enter the atmosphere once every few years but tend to go unheralded outside the asteroid-hazard community because they enter over oceans or vast stretches of uninhabited land.?
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