On 15 February 2013, an Apollo asteroid entered Earth’s atmosphere over Russia at about 09:20 YEKT (03:20 UTC) with an estimated speed of 18 km/s (40,000 mph); it became a brilliant superbolide meteor over the southern Ural region. The dazzling light of the meteor was bright enough to cast moving shadows during the morning daylight in Chelyabinsk and was observed from Sverdlovsk, Tyumen, Orenburg Oblasts, the Republic of Bashkortostan, and in Kazakhstan. Eyewitnesses also felt intense heat from the fireball.
The object exploded in an air burst over Chelyabinsk Oblast at a height of about 15 to 25 km (9.3 to 15.5 mi), with 23.3 km (14.5 mi) being the most recent official burst height. It exploded with the generation of a bright flash, small fragmentary meteorites and a powerful shock wave. The atmosphere absorbed most of the object’s energy, with a total kinetic energy before atmospheric impact equivalent to ~ 440 kilotons of TNT (~ 1.8 PJ). This is about 20–30 times more energy than was released from the atomic bombs detonated at Hiroshima and Nagasaki, but much less than the 50 to 57 Mt (210 to 240 PJ) Tsar bomb. Also, unlike a nuclear explosion the object and its fragments did not release all of its energy at once, with the total radiated energy of the fireball, which generated the main explosion, predicted to have emitted an energy equivalent to ~ 90 kilotons of TNT (~ 0.4 PJ), according to NASA’s Jet Propulsion Laboratory.
About 1,500 people were injured, two seriously. All of the injuries were due to indirect effects rather than the meteor itself, mainly from broken glass from windows that were blown in when the shock wave arrived, several minutes after the bright flash. Initially 4,300, later 7,200 buildings in six cities across the region were reported to have been damaged by the explosion.
With an estimated initial mass of 11,000 tonnes, and measuring approximately 17 to 20 meters across, the Chelyabinsk meteor is the largest object known to have entered Earth’s atmosphere since the 1908 Tunguska event and the 1930 Brazilian event, and it is the only meteor known to have resulted in a large number of injuries. The object had not been detected before atmospheric entry.