The asteroid's breakup at an altitude some 12 to 15 miles above Russia's Chelyabinsk region represents the largest recorded asteroid encounter since 1908, when another asteroid or comet exploded over the Tunguska River in Siberia, leveling some 820 square miles of forest, says Paul Chodas, a scientist with the near-Earth object program at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
The shock waves from what appear to have been multiple blasts, perhaps triggered as large initial fragments underwent their own disruption, broke windows in the three major cities in the region, including Chelyabinsk. At least 950 people were injured, although most of the injuries were minor, according to reports from the area.
"What an amazing day for near-Earth objects. By an incredible coincidence we have two rare events happening on the very same day," Dr. Chodas said during a briefing Friday afternoon.
Asteroid 2012 DA14 set a record for the closest approach to Earth of an asteroid in its size class humans so far have detected. And the Chelyabinsk blast occurs on average once every hundred years, based on the revised size and mass estimate for the asteroid that triggered it.