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In 2016, the United Nations designated June 30 each year as “Asteroid Day” to raise public awareness about the danger of an asteroid impact. But why June 30? Because it is the anniversary of Tunguska, a massive 12-megaton explosion that occurred in Siberia, Russia.
What was the Tunguska eruption?
In 1908, a man was sitting on the front porch of a trading station in Vanavara in Siberia. Within a few moments he was thrown from his chair to the ground and it was so hot he felt his shirt on fire. This is how an eyewitness described the event while sitting more than 60 kilometers from the epicenter, according to NASA.
On June 30 of that year, a massive explosion near the Podkamennaya Tunguska River in the region flattened an estimated 80 million trees covering an area of ​​more than 2,150 square kilometers, according to CBC. Siberia is sparsely populated, but eyewitness accounts from the time speak of a “fire-dispersed sky”.
The event was followed by a powerful earthquake that shattered windows hundreds of kilometers away and even knocked people off their feet, according to EarthSky. While the eruption was a stunningly dramatic event, a few decades later there was an explanation for it.
Trees radiate away from the epicenter of the blast. (Image credit: Leonid Kulik via The Conversation)
The interesting Tunguska impact occurred because the meteorite did not leave behind a crater. The best explanation for this event is that an asteroid or comet, about 50 meters across, explodes in the atmosphere between six to ten kilometers above the surface. Scientists believe that the asteroid exploded in the atmosphere, causing what is known as an airburst.
The blast released energy equivalent to 185 times that released during the atomic bombing of Hiroshima, he said The New Yorker.
Why did it take so long to explain the Tunguska eruption?
The impact occurred in 1908 but scientists first reached the area about 19 years later, according to NASA. After an earlier attempt to reach the region had been thwarted by the harsh Siberian winter, Leonid Kulik, chief curator of the St. Petersburg Museum’s meteorite collection at the time, arrived there in 1927.
According to Don Yeomans, a retired NASA planetary scientist, the locals were reluctant to talk to Kulick about the event, believing the eruption was caused by the god Ogdi who cursed the area by breaking down trees and killing animals.
Although eyewitness accounts were hard to come by, there was enough evidence to get around. Eight million trees were lying on the ground and they created a radial pattern pointing straight away from the epicenter of the explosion.
According to some estimates, the asteroid entered our planet at a speed of more than 5,300 kilometers per hour. The asteroid weighing about 100,000 kilograms would have heated the air around it to a temperature of about 25,000 degrees Celsius. At about 7.17am Siberian time that day, the combination of pressure and heat would have caused the asteroid to explode, creating a fireball and releasing all that energy.
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