The planetary science director at the U.S. space agency, NASA, says the huge meteor that streaked across the sky and exploded above Russia's Ural Mountains on Friday was an "exception."
Jim Green says "fireballs" of this kind happen on a daily basis, but most of them are not seen because they fall over the ocean or in remote areas.
People in Russia's Chelyabinsk region panicked as the 10-ton meteor lit up the morning sky.
Its explosion unleashed a shock wave that blew out windows, damaged buildings and left more than 1,100 people injured. The Interior Ministry said most of the injuries were caused by flying glass.
The Russian Academy of Sciences says the meteor entered the Earth's atmosphere at a speed of at least 54,000 kilometers per hour.
Its entry occurred just hours before an asteroid known as 2012 DA14 had a close encounter with Earth. There was no connection between the two incidents.
NASA said the 45-meter-wide asteroid came as close as 27,000 kilometers above Earth.