On the morning of June 30, 1908, a huge ball of fire was observed streaking across the sky in a remote part of Siberia, in Russia. No one knew what it was at the time, but whatever its origins, it exploded above the Podkamennaya Tunguska River, flattening nearly 800 square miles of forest. This strange occurrence came to be known as the Tunguska Event.
It was fortunate that the explosion took place where it did, in the middle of the wilderness where no humans were present, because the force of the blast was about 1,000 times greater than that of the atomic bomb that was dropped on Hiroshima, Japan in World War II. Some 80 million trees were destroyed, countless animals were killed, and there was even some minor damage to buildings that were outside of the explosion’s impact zone. Had this occurred near a major population center, the human death toll would have been staggering.
The force of the Event was recorded at seismic stations across Europe and Asia. The blast produced a shock wave equivalent to that of an earthquake measuring 5.0 on the Richter scale. Changes in the atmosphere were detected as far away as the United Kingdom. And for several days, the skies in Asia and Europe glowed with an eerie light at night.
The area where the Event occurred was hard to get to at the time, so it wasn’t until 1927 that researchers were able to get to the site of the explosion. Expecting to find evidence of a meteorite, the scientists found nothing except flattened trees. There was no crater and no meteorite fragments.
This strangeness led to various wild theories and explanations for the Tunguska Event. These theories have ranged from alien attack to an encounter with a small black hole. The truth behind the Event is much less exciting, though.
We now know that the blast was most likely caused by either a stony asteroid or icy comet that struck the Earth’s atmosphere. The comet or asteroid (we’ll probably never know for sure which one it was) exploded when it reached the atmosphere and never actually hit the ground. This created an air burst that destroyed that area of forest in the Siberian wilderness. Since it never touched the ground there was no crater, and any particles from the object disintegrated in the explosion.
Thankfully, astronomers today have a much better grasp on the workings of the solar system. They regularly track such Near-Earth Objects as the one that caused the Tunguska Event. They also regularly meet to plan what to do in case such an object is on a collision course with Earth.