What was the Tunguska explosion of 1908, and how did Chelyabinsk in 2013 compare?

On 30 June 1908 a large explosion happened over Central Siberia, in a remote region of taiga near the Podkamennaya Tunguska River. Research later found that it devastated nearly 2,150 square kilometres of forest in a radial pattern, which implies an explosion in the air. The scientific consensus is that it was a meteor air burst, although no fragment has been formally identified.

Researchers favour a meteoroid 50 to 60 metres wide that exploded 5 to 10 kilometres up, releasing an energy often estimated at 10 to 15 megatons of TNT, though published estimates range from 3 to 30 megatons. The site was remote, so the main evidence came later: the press reported the blast, but a first scientific expedition came only in 1921, led by Leonid Kulik, who found the epicentre in 1927. Whether it was an asteroid or a comet is still debated.

The effects were not only local. On the evening of 30 June, bright nights of rare intensity covered a vast area of Eurasia, so bright that it was possible to read a newspaper around midnight without artificial light.

Over a century later, on 15 February 2013, the Chelyabinsk meteor entered the atmosphere over Russia's southern Ural region. NASA estimated it at about 17 to 20 metres across. Its energy is estimated at 400 to 500 kilotonnes of TNT, about 30 times the Hiroshima bomb, mostly absorbed by the atmosphere as a shock wave. It was the largest object to enter the atmosphere since Tunguska. 1,491 people sought medical treatment, mostly for broken window glass, and no deaths were reported.