The Chelyabinsk Meteor of 2013: Airburst Over Russia

The morning of February 15, 2013

The object was a stony asteroid fragment about 20 meters (66 feet) across, the Planetary Society says. NASA describes it as house-sized, and its Tunguska article compares it with a five-story building. It entered the atmosphere at a relatively shallow angle, at about 19 km/s (69,000 km/h, or 42,690 mph) by the Planetary Society's figure, and NASA's fact page says over 18 km/s. It did not reach the ground intact. It exploded in the air at roughly 24 to 30 km (15 to 19 miles) up, an airburst, and most of the energy of the blast went into the atmosphere.

Different agencies give different numbers because the values come from different analyses. The table gives ranges and says where each comes from.

A kiloton is the energy of a thousand tons of TNT. The Planetary Society's estimate of 500 kilotons is about 30 times the energy of the Hiroshima bomb, a comparison the Society makes in its own article.

The shock wave, the injuries and the damage

The damage came from the shock wave, not from falling rock. NASA says it broke windows across roughly 520 square km (200 square miles) and damaged some buildings. The Planetary Society reports that about 1,500 people went to local hospitals and clinics. Most of the injuries came from flying glass when the shock wave shattered windows, and the Society says many people had gone to their windows to look at the flash. Early NASA reports spoke of hundreds of injuries, and the later counts are higher.

The NASA workshop report cites an analysis by Peter Jenniskens and colleagues that estimates 1% of local inhabitants were injured, most not seriously, and that about 2% of people outdoors were "sunburned" by radiant heat from the blast. Those figures show something a forest cannot: how people react to a fireball. Tunguska struck a very thinly populated region, so its effects on people are poorly documented, which is one reason Chelyabinsk matters. The 1908 Tunguska airburst is the larger and less well-recorded case.

What the videos and sensors recorded

Dashcam videos captured the streak and the flash, the Planetary Society notes. NASA scientists then turned that flood of footage into data. A 2015 conference paper by William Cooke of NASA's Meteoroid Environment Office and colleagues calls Chelyabinsk the first major impact event in the era of social media and 24-hour news. Researchers who would usually take days or weeks to analyze a fireball had to give answers in hours.

They did it by geolocating YouTube videos with Google Street View, reading eyewitness reports on social media, and combining those with infrasound data, the low-frequency pressure waves that travel through air. The paper says this gave a fairly accurate picture of the event within a few hours, and that it ruled out a link between the fireball and asteroid 2012 DA14, which passed near Earth later the same day. That asteroid is now numbered 367943 Duende and is about 30 meters across, according to the Planetary Society.

The workshop report adds that the Chelyabinsk event, with its documented light curve, let modelers test their codes. Models can now reproduce the altitude where the object deposited most of its energy, the pattern of destruction on the ground and the light curve, including three flares with peak energy deposition at about 30 km. How fireballs and bolides are measured and reported explains what a light curve is and how bright events like this are logged.

The fragments on the ground

Pieces did reach the ground, after the airburst. A NASA-hosted conference abstract from 2014 says the meteorite is classified as an LL5 chondrite, a kind of ordinary chondrite, that its pre-atmospheric diameter was about 20 m, and that fragments totaling much more than 100 kg were collected. The authors measured noble gases in 13 fragments to study the rock's exposure history and the thermal history of its parent asteroid. The main types of meteorites explains how a chondrite differs from an iron or stony-iron rock.

Most of the mass broke up in the air, and the survivors landed as scattered fragments. That is a very different outcome from the iron impactor behind the crater described in how impact craters form and are confirmed.

What it taught about detection

Nobody saw this object coming. The Planetary Society says it was not detected until it was already in the atmosphere, largely because it approached from the direction of the Sun and was hidden in the glare. The same article points to NASA's NEO Surveyor spacecraft as a future tool for finding such asteroids sooner and calculating their paths. For that mission's current status, check NASA's planetary defense pages, because this article has not verified it.

The other change was in speed of response. The Cooke paper says NASA's Meteoroid Environment Office and the Meteor Physics Group at Western University had been building tools since 2008, including automated Twitter monitoring, and that these were used within hours of the event. NASA's Tunguska article says that, under current population estimates, an object like Chelyabinsk hits Earth every 10 to 100 years on average, and the workshop report puts it at about once per century. Those are long-term averages with wide uncertainty, not a schedule. How agencies approach the larger question is covered in how planetary defense works, including the DART test.

Common mistakes and myths

• "A meteorite crashed into Chelyabinsk." The object exploded high above the city. The damage was a shock wave. Fragments fell afterward, over a wide area.
• "The asteroid that passed Earth that day caused it." The 2015 Cooke paper reports that analysis ruled out any connection with 2012 DA14.
• "Falling rock injured the crowds." The Planetary Society says most injuries came from flying glass when windows shattered, and from people looking at the flash.
• "The size and energy are settled numbers." They are estimates. NASA and the Planetary Society give about 440 to 550 kilotons of energy in different places, so treat any single number with care.
• "It was a comet." The recovered fragments are an LL5 ordinary chondrite, a stony meteorite type, which points to an asteroid origin.

Frequently asked questions

Was the Chelyabinsk object an asteroid or a comet?

It was a stony asteroid fragment. NASA calls it a stony asteroid, and the recovered meteorite is classified as an LL5 chondrite.

How big was it?

About 20 meters (66 feet) across before it entered the atmosphere, according to the Planetary Society and a NASA-hosted abstract. NASA calls it house-sized.

How many people were hurt?

About 1,500 people sought medical care, by the Planetary Society's count and a NASA-hosted abstract. Most of the injuries came from broken glass. Early NASA statements mentioned hundreds.

Why was it not seen coming?

It was not detected until it was in the atmosphere. The Planetary Society says it approached from the direction of the Sun, whose glare hid it from telescopes.