The Tunguska event

What caused this mid-air explosion over Russia more than 100 years ago?

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On the morning of 30 June 1908, the sky split in two over the forest near the Podkamennaya Tunguska River in Siberia and then a mid-air explosion rocked the area.

1. Entry – The object enters Earth’s atmosphere with a burst of light so bright that it hurts witnesses’ eyes.
1. Entry – The object enters Earth’s atmosphere with a burst of light so bright that it hurts witnesses’ eyes.

It had the estimated energy of a 15-megaton bomb – roughly a thousand times more powerful than the atomic bomb dropped on Hiroshima and millions of times more energetic than any of the man-made explosives of the day. The source of this big bang could only be extra-terrestrial.

2. Explosion – An enormous fireball erupts as the space rock explodes 10km (6.2mi) up.
2. Explosion – An enormous fireball erupts as the space rock explodes 10km (6.2mi) up.

The Tunguska event, as it later became known, was most likely a large asteroid or comet up to 100 metres (328 feet) in diameter that – going on the lack of an impact crater – exploded in mid-air about ten kilometres (6.2 miles) up. The resulting fireball and shockwave charred 100 square kilometres (38.6 square miles) and knocked 80 million trees flat in an instant.

3. Devastation – Millions of trees are felled over thousands of square kilometres by a mighty shockwave even felt in neighbouring continents.
3. Devastation – Millions of trees are felled over thousands of square kilometres by a mighty shockwave even felt in neighbouring continents.

The Tunguska object was around five times the size of the Apollo meteor that entered Earth’s atmosphere and exploded over Chelyabinsk in February 2013. Objects of this size enter Earth’s atmosphere only once every few centuries and the Tunguska event is one of the largest in recorded history. Despite the remote location, there were a few witnesses, who spoke of a light as bright as the Sun, followed by an explosive crack, powerful seismic tremors and a brief, unbearable heat. Indeed the scorching temperatures caused most trees to briefly char, but the proceeding shockwave blew out any flames before they could burn.

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