What was the Tunguska event of 1908?

The Tunguska event was a large explosion that occurred on the morning of 30 June 1908 in central Siberia, then part of the Russian Empire. The scientific consensus attributes it to a meteor air burst, the atmospheric explosion of a celestial body, although no fragment has been formally identified. It is regarded as the largest impact event in recorded history, even though nothing seems to have struck the ground. [1] [2]

At about 7:15 am local time, Evenki reindeer herders described a fireball trailing smoke, then a flash brighter than the Sun, followed by a noise like thunder. Those closest said they were thrown into the air and knocked unconscious, and their dwellings were damaged or destroyed. Because the region is sparsely populated, few people died, though herds of reindeer were reported lost. Wikipedia states that at least three people were killed and windows shattered within about 200 km. Seismic stations in Russia and Germany recorded the blast, and atmospheric waves were detected worldwide. [3] [1]

The first scientific expedition to reach the site was led by geologist Leonid Kulik in 1927, nearly two decades later. Near the centre he found trees still standing but stripped of branches and bark, with signs of burning. Later surveys outlined a butterfly-shaped zone of destruction with millions of trees knocked down in a radial pattern pointing away from the centre. That pattern implied an explosion in the air rather than an impact on the surface. Estimates of the area vary by source: NASA's history article gives 830 square miles, which matches the roughly 2,150 square kilometres cited by Wikipedia, while the Royal Observatory Greenwich gives 1,287 square kilometres for the flattened forest. [3] [1] [2]

Estimates differ by source. NASA Science gives 50 to 100 metres across, Wikipedia favours 50 to 60 metres, and EarthSky describes a stony asteroid of about 50 to 80 metres travelling at roughly 54,000 km per hour. Most estimates place the explosion 5 to 10 km above the surface, with an energy often put at 10 to 15 megatons of TNT. The Royal Observatory Greenwich compares it to 185 Hiroshima bombs. [4] [1] [5] [2]

Most scientists today believe the object was an asteroid. A comet was proposed in 1930, possibly a fragment of comet Encke, and the debate over asteroid versus comet is described as still open. Terrestrial explanations such as an underground gas explosion have been suggested but remain marginal. Direct evidence of the object is elusive. Microparticles of apparent extraterrestrial origin have been found but could not be conclusively tied to the blast. Some researchers have proposed that Lake Cheko formed from a fragment, while other teams dispute this. [3] [2] [1] [4]