BERLIN — A meteor exploded in the sky above Russia's Ural Mountains on Friday, causing a shockwave that blew out countless windows and injured hundreds of people with flying glass. Here's a look at those objects in the sky:
Q. What's the difference between a meteor and a meteorite?
A. Meteors are pieces of space rock, usually from larger comets or asteroids, which enter the Earth's atmosphere. Many are burned up by friction and the heat of the atmosphere, but those that survive and strike the Earth are called meteorites. They often hit the ground at tremendous speed — up to 30,000 kilometers an hour (18,650 mph) — releasing a huge amount of energy, according to the European Space Agency.
Q: How common are meteorite strikes?
A: Experts say smaller strikes happen five to 10 times a year. Large meteors such as the one Friday in Russia are rarer, but still occur about every five years, according to Addi Bischoff, a mineralogist at the University of Muenster in Germany. Most of them fall over uninhabited areas where they don't injure humans.
Q: How big was Friday's bang in Russia, and why did it cause so many injuries?
A: Alan Harris, a senior scientist at the German Aerospace Center in Berlin, said most of the damage would have been caused by the blast — or blasts — as the meteor broke up in the atmosphere. The rapid deceleration of the meteor released a huge amount of energy that would have been heard and felt many miles away. Witnesses say it shattered windows and sent loose objects flying through the air.
While estimates of the mass of the meteor range from 10-100 tons, and it is still unclear if it was made of rock or iron, "the explosive force of the airburst might have been some 10 kilotons of TNT," said Harris. But he noted that since the blast occurred several miles above the Earth, the damage isn't comparable to an explosion of that magnitude on the Earth' surface.
By comparison, the U.S. bomb dropped over Hiroshima during World War II had an explosive force of about 15 kilotons, but it detonated just 2,000 feet above a densely populated city.
Q: Is there any link between this meteor and the asteroid fly-by taking place later Friday?
A: No, it's just cosmic coincidence, according to European Space Agency spokesman Bernhard von Weyhe, who says Asteroid 2012DA14 is unrelated to the meteorite strike in Russia.
Q: When was the last comparable meteorite strike?
A: In 2008, astronomers spotted a meteor similar to the one in Russia heading toward Earth about 20 hours before it entered the atmosphere. It exploded over the vast African nation of Sudan, causing no known injuries.
The largest known meteor in recent times caused the "Tunguska event" — flattening thousands of square miles of forest in remote Siberia in 1908. Nobody was injured by the meteor blast, nor by the the Sikhote-Alin meteorite that fell in eastern Siberia in 1947.