Chelyabinsk

The 2013 airburst over Russia that shattered thousands of windows and reminded the world that asteroid impacts still happen.

Key facts

Type

Ordinary chondrite (LL5)

Fell or found

Fell (witnessed and widely filmed)

Year

2013 (15 February)

Country

Russia

Mass

asteroid of about 12,000 tonnes; roughly 1 tonne of fragments recovered

Official name

Chelyabinsk

At about 9.20 in the morning on 15 February 2013, people in and around the city of Chelyabinsk in Russia's southern Ural region saw a fireball so bright that, for a moment, it outshone the Sun. Dashboard cameras, security cameras and phones recorded it streaking across the sky, leaving a thick, glowing trail. Then, after an eerie silence lasting a minute or more, a shock wave hit. Windows burst across the city, doors were blown in, and a factory roof partly collapsed.

What happened

An asteroid about 18 metres across, with a mass estimated at roughly 12,000 tonnes, had entered the atmosphere at about 19 kilometres per second, travelling at a shallow angle. Air pressure built up in front of it until the rock broke apart violently at an altitude of roughly 30 kilometres. Most of its energy was released as heat and a blast wave in the air, an event called an airburst. Scientists estimate the energy at around 400 to 500 kilotonnes of TNT, roughly 30 times the energy of the atomic bomb dropped on Hiroshima, although spread through the air rather than concentrated at the ground.

About 1,500 people needed medical help, most of them for cuts from flying glass. Many had gone to their windows to see what had caused the flash, just in time for the shock wave to arrive. More than 7,000 buildings were damaged. Remarkably, no one was killed. Infrasound stations built to detect nuclear tests picked up the deep, low-frequency sound of the blast around the world. It was the largest natural object known to have entered Earth's atmosphere since the Tunguska event of 1908.

The meteorites

Most of the asteroid was turned to dust and vapour, but many fragments survived. Thousands of small stones were picked up from snowfields, many with fresh black fusion crust, the thin glassy skin that forms when a meteorite's surface melts during its fall. A large piece punched a hole roughly 7 metres wide in the ice of Lake Chebarkul. Divers later recovered from the lake bed a mass weighing well over 500 kilograms, which is now displayed in a museum in Chelyabinsk.

The meteorite is an LL5 ordinary chondrite. Ordinary chondrites are the most common type of meteorite to fall; 'LL' means it is low in total iron and low in metal, and '5' indicates it was heated and recrystallised inside its parent asteroid. Many Chelyabinsk stones are crossed by dark veins of shock melt, created by violent collisions in space long before it reached Earth.

Coincidence in the sky

By chance, on the same day, a different asteroid called 2012 DA14 passed very close to Earth, closer than some communications satellites. Astronomers had been tracking that one carefully. The Chelyabinsk asteroid had a completely different orbit and was unrelated. It approached from the direction of the Sun, so telescopes looking at the night sky could not have seen it coming.

Why it matters

Chelyabinsk transformed how the world thinks about smaller asteroids. Before 2013, much attention focused on the rare kilometre-sized bodies that could cause global catastrophe. Chelyabinsk showed that an object only the size of a house can injure many people. Its abundant video footage allowed scientists to reconstruct its path and orbit in great detail, and it helped spur international work on planetary defence, including better sky surveys and agreed plans for warning the public.

It also carries a simple safety lesson. If you ever see an extraordinarily bright flash in the sky, stay away from windows for a few minutes, just as you would during a storm. Any shock wave travels more slowly than light, so the glass may not break until well after the flash.

Did you know?

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Chelyabinsk in the catalogue