The Chelyabinsk meteor () was a superbolide that entered Earth's atmosphere over the southern Ural region in Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). It was caused by an approximately , near-Earth asteroid that entered the atmosphere at a shallow 18‐degree angle with a speed relative to Earth of about . The light from the meteor was briefly brighter than the Sun (which is about −26.7 magnitude), visible as far as away. It was observed in a wide area of the region and in neighbouring republics. Some eyewitnesses also reported feeling intense heat from the fireball.
The object exploded in a meteor air burst over Chelyabinsk Oblast, at a height of about . The explosion generated a bright flash, producing a hot cloud of dust and gas that penetrated to , and many surviving small fragmentary meteorites. Most of the object's energy was absorbed by the atmosphere, creating a large shock wave. The asteroid had a total kinetic energy before atmospheric impact equivalent to the blast yield of , estimated from infrasound and seismic measurements. This was approximately 30 times as much energy as that released by the atomic bomb detonated at Hiroshima.best estimate of the equivalent nuclear blast yield of the Chelyabinsk explosion
The object approached Earth undetected before its atmospheric entry, in part because its radiant (source direction) was close to the Sun. 1,491 people were injured seriously enough to seek medical treatment. 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, minutes after the superbolide's flash. Around 7,200 buildings in six cities across the region were damaged by the explosion's shock wave, and authorities scrambled to help repair the structures in sub-freezing temperatures. No deaths were reported.
It is the largest object to have entered Earth's atmosphere since the 1908 Tunguska event, which destroyed a wide, remote, forested, and very sparsely populated area of Siberia.
The earlier-predicted and well-publicized close approach of a larger asteroid on the same day, the roughly 367943 Duende, occurred about 16 hours later; the very different orbits of the two objects showed they were unrelated to each other.
Initial reports
Local residents witnessed extremely bright burning objects in the sky in Chelyabinsk, Kurgan, Sverdlovsk, Tyumen, and Orenburg Oblasts, the Republic of Bashkortostan, and in neighbouring regions in Kazakhstan, when the asteroid entered the Earth's atmosphere over Russia. Amateur videos showed a fireball streaking across the sky and a loud boom several minutes afterwards. Some eyewitnesses experienced skin and retinal burns from the fireball.
The event began at 09:20:21 Yekaterinburg time (which was UTC+6 at the time), several minutes after sunrise in Chelyabinsk, and minutes before sunrise in Yekaterinburg. According to eyewitnesses, the bolide appeared brighter than the sun, as was later confirmed by NASA. An image of the object was also taken soon after it entered the atmosphere by the weather satellite Meteosat 9. Witnesses in Chelyabinsk said that the air of the city smelled like "gunpowder", "sulfur" and "burning odors" starting about 1 hour after the fireball and lasting all day.
Atmospheric entry
The visible phenomenon due to the passage of an asteroid or meteoroid through the atmosphere is termed a meteor. If the object reaches the ground, then it is termed a meteorite. During the Chelyabinsk meteoroid's traversal, there was a bright object trailing smoke, then an air burst (explosion) that caused a powerful blast wave. The latter was the only cause of the damage to thousands of buildings in Chelyabinsk and its neighbouring towns. The fragments then entered dark flight (without the emission of light) and created a strewn field of numerous meteorites on the snow-covered ground (officially named Chelyabinsk meteorites).
The last time a similar phenomenon was observed in the Chelyabinsk region was the Kunashak meteor shower of 1949, after which scientists recovered about weighing more than in total. The Chelyabinsk meteor is thought to be the biggest natural space object to enter Earth's atmosphere since the 1908 Tunguska event, and the only one confirmed to have resulted in many injuries,Historical, normally accurate, Chinese records of the 1490 Qingyang event describe over 10,000 deaths, but it is not confirmed as an impact event. although a small number of panic-related injuries occurred during the Great Madrid Meteor Event of 10 February 1896.
Preliminary estimates released by the Russian Federal Space Agency indicated the object was an asteroid moving at about in a "low trajectory" when it entered Earth's atmosphere. According to the Russian Academy of Sciences, the meteor then pushed through the atmosphere at a velocity of Video recordings show the radiant of the meteor (its apparent position of origin in the sky) above and to the left of the rising Sun.
Early analysis of CCTV and dashcam video posted online indicated that the meteor approached from the southeast, and exploded about south of central Chelyabinsk above Korkino at a height of , with fragments continuing in the direction of Lake Chebarkul. On 1 March 2013, NASA published a detailed synopsis of the event, stating that at peak brightness (at 09:20:33 local time), the meteor was high, located at 54.8°N, 61.1°E. At that time it was travelling at about – almost 60 times the speed of sound.NASA's webpage in turn acknowledges credit for its data and visual diagrams to: Peter Brown (University of Western Ontario); William Cooke (Marshall Space Flight Center); Paul Chodas, Steve Chesley and Ron Baalke (JPL); Richard Binzel (MIT); and Dan Adamo. During November 2013, results were published based on a more careful calibration of dashcam videos in the field weeks after the event during a Russian Academy of Sciences field study, which estimated the point of peak brightness at altitude and the final disruption of the thermal debris cloud at , settling to , all with a possible systematic uncertainty of ±.
The United States space agency NASA estimated the diameter of the bolide at about and has revised the mass several times from an initial , until reaching a final estimate of . The air burst's blast wave, when it hit the ground, produced a seismic wave which registered on seismographs at magnitude () 4.2.
The Russian Geographical Society said the passing of the meteor over Chelyabinsk caused three blasts of different energy. The first explosion was the most powerful, and was preceded by a bright flash, which lasted about five seconds. Initial newspaper altitude estimates ranged from , with an explosive equivalent, according to NASA, of roughly , although there is some debate on this yield (500 kilotonnes is exactly the same energy released by the Ivy King nuclear explosion in 1952). According to a paper in 2013, all these 500-kiloton yield estimates for the meteor airburst are "uncertain by a factor of two because of a lack of calibration data at those high energies and altitudes". Because of this, some studies have suggested the explosion to have been as powerful as , which would mean a more powerful explosion than Tunguska and comparable to the Tsar Bomba.
The hypocentre of the explosion was to the south of Chelyabinsk, in Yemanzhelinsk and Yuzhnouralsk. Due to the height of the air burst, the atmosphere absorbed most of the explosion's energy. The explosion's blast wave first reached Chelyabinsk and environs between less than 2 minutes 23 seconds and 2 minutes 57 seconds later. The object did not release all of its kinetic energy in the form of a blast wave, as some of the total energy of the main airburst's fireball was emitted as visible light according to NASA's Jet Propulsion Laboratory, and two main fragments survived the primary airburst disruption at ; they flared around , with one falling apart at and the other remaining luminous down to , with part of the meteoroid continuing on its general trajectory to punch a hole in the frozen Lake Chebarkul, an impact that was fortuitously captured on camera and released in November 2013.
The infrasound waves given off by the explosions were detected by 20 monitoring stations designed to detect nuclear weapons testing managed by the Comprehensive Test Ban Treaty Organization (CTBTO) Preparatory Commission, including the distant Antarctic station, some away. The blast of the explosion was large enough to generate infrasound returns, after circling the globe, at distances as far as about . Multiple arrivals involving waves that travelled twice around the globe have been identified. The meteor explosion produced the largest infrasounds to be recorded by the CTBTO infrasound monitoring system up to that point since recording began in 2001 (only since surpassed by the 2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami), so great that they reverberated around the world several times, taking more than a day to dissipate. Additional scientific analysis of US military infrasound data was aided by an agreement reached with US authorities to allow its use by civilian scientists, implemented only about a month before the Chelyabinsk meteor event.
A preliminary estimate of the explosive energy by astronomer Boris Shustov, director of the Russian Academy of Sciences Institute of Astronomy, was , another using empirical period-yield scaling relations and the infrasound records, by Peter Brown of the University of Western Ontario gave a value of and represents a best estimate for the yield of this airburst; there remains a potential "uncertainty [in the order of] a factor of two in this yield value". Brown and his colleagues also went on to publish a paper in November 2013 which stated that the "widely referenced technique of estimating airburst damage does not reproduce the [Chelyabinsk] observations, and that the mathematical relations found in the book The Effects of Nuclear Weapons which are based on the effects of nuclear weapons – [which is] almost always used with this technique – overestimate blast damage [when applied to meteor airbursts]". A similar overestimate of the explosive yield of the Tunguska airburst also exists; as incoming celestial objects have rapid directional motion, the object causes stronger blast wave and thermal radiation pulses at the ground surface than would be predicted by a stationary object exploding, limited to the height at which the blast was initiated-where the object's "momentum is ignored". Thus, a meteor airburst of a given energy is "much more damaging than an equivalent [energy] nuclear explosion at the same altitude". The seismic wave produced when the primary airburst's blast struck the ground yields a rather uncertain "best estimate" of 430 kilotons (momentum ignored).
Brown also states that the double smoke plume formation, as seen in photographs, is believed to have coincided near the primary airburst section of the dust trail (as also pictured following the Tagish Lake fireball), and it likely indicates where rising air quickly flowed into the center of the trail, essentially in the same manner as a moving 3D version of a mushroom cloud. Photographs of this smoke trail portion, before it split into two plumes, show this cigar-shaped region glowing incandescently for a few seconds. This region is the area in which the maximum of material ablation occurred, with the double plume persisting for a time and then appearing to rejoin or close up.
Injuries and damage