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Q. What’s the difference between a meteor and a meteorite?

A. Meteors are pieces of space rock, usually from larger comets or asteroids, that 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 18,650 mph) — releasing a huge amount of energy, according to the European Space Agency.

Q: How often do meteorites hit Earth?

A: Experts say smaller strikes happen five to 10 times a year. Large meteors such as the one in Russia on Friday 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 meteor and why did it cause so many injuries?

A: Before it entered the atmosphere, the meteor was about 16 yards in diameter, NASA says.

The blast released the equivalent of hundreds of thousands of tons of TNT. The huge release of energy shattered windows and sent loose objects flying.

Q: Is there any link between this meteor and the larger asteroid that passed Earth later Friday?

A: No, it’s just a coincidence. According to NASA, the trajectory of the Russian meteorite was significantly different than that of asteroid 2012 DA14. “In videos of the meteor, it is seen to pass from left to right in front of the rising sun, which means it was traveling from north to south. Asteroid DA14’s trajectory is in the opposite direction, from south to north,” the U.S. space agency said.

Q: When was the last event like this?

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, or by the Sikhote-Alin meteorite that fell in eastern Siberia in 1947.

Scientists believe that a far larger meteorite strike on what today is Mexico’s Yucatan Peninsula may have been responsible for the extinction of the dinosaurs about 66 million years ago. According to that theory, the impact would have thrown up vast amounts of dust that blanketed the sky for decades and altered the climate on Earth.

Q: What can scientists learn from Friday’s strike?

A: Bischoff says scientists and treasure hunters are probably already racing to find pieces of the space rock. Some meteorites can be very valuable, selling for up to $670 per gram, depending on their origin and composition. Because meteors have remained largely unchanged for billions of years — unlike rocks on Earth affected by erosion and volcanic outbreaks — scientists will study the fragments to learn more about the early universe.

Alan Harris, a senior scientist at the German Aerospace Center in Berlin, says some meteorites are also believed to carry organic material and may have influenced the development of life on Earth.

“It’s a global challenge and we need to find a solution together,” he said. “But one thing’s for sure, the Bruce Willis ‘Armageddon’ method won’t work.”

Associated Press

Alan Fredman is a retired copy editor for the St. Louis Post-Dispatch.