On June 30, 1908, an explosion struck on a warm summer morning in Siberia, Russia. Also known as the "Tunguska explosion," the event happened over the sparsely populated northern forestland above the Podkamennaya Tunguska River, which is presently Krasnoyarsk Krai.
The blast released energy that killed reindeer and flattened an estimated 80 million trees over 830 square miles (2,150 square kilometers). According to witnesses, they saw a bluish fireball moving across the sky. They also reported observing a flash and a sound similar to artillery fire following the explosion. Furthermore, a powerful shockwave damaged windows hundreds of miles away and knocked people off their feet.
What Caused the Tunguska Explosion?
It took a long time for scientists to understand the cause of the Tunguska event. It was almost two decades before the first scientists reached this remote region of Siberia. The first Soviet research expedition to investigate the possibility was led by Leonid Kulik in 1927. He made an initial trip to the area, interviewed local witnesses, and explored the region of fallen trees.
What makes the Tunguska event mysterious is the fact that no one ever found a crater. Still, scientists categorize it as an impact event. They believe the incoming object never struck Earth but instead exploded in the atmosphere and caused an air burst. Such an atmospheric blast was still enough to cause extensive damage to the forest in the region.
Scientists are convinced that the object was likely a stony asteroid approximately as giant as a 25-story building. They believe that the asteroid traveled at a speed of about 33,500 miles (54,000 km) per hour and exploded 3 to 6 miles (5 to 10 km) above the surface of the Earth.
The Tunguska event happened again 105 years later but on a smaller scale. On February 15, 2013, a similar but smaller airburst due to a meteor occurred over Chelyabinsk, Russia, about 1,500 miles (2,400 km) west of Tunguska.
Scientists called this the Chelyabinsk event, which provided clues as to what happened during the Tunguska event. According to NASA, this highly documented fireball allowed them to apply modern computing modeling techniques to explain what was seen, heard and felt.
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Preparing for Future Events
Based on the current understanding of the asteroid population, an object similar to the Chelyabinsk meteor can strike the Earth every 10 to 100 years on average. In 2019, a team of researchers studied the Tunguska event. The research was inspired by a workshop held at NASA's Ames Research Center in Silicon Valley and sponsored by the NASA Planetary Defense Coordination Office.
Due to the effects of the Tunguska event and other smaller impacts, astronomers take the possibility of catastrophic comet and asteroid impacts seriously. They are now observing programs to watch for near-Earth objects and prepare for possible collisions on Earth. As NASA finds new asteroids, they track their orbits and refine their impact possibilities using advanced telescopes and robotic space missions to study them up close.
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