On June 30, 1908, in the forests of the Tunguska River, in Siberia, at 8 hours and 17 minutes local time, there was a violent explosion. An immense forest area of approximately 2,200 square kilometers was completely destroyed; in its center everything was destroyed, and around it all the trees fell radially, pointing towards the center, while whole herds of reindeer were annihilated.
Fortunately, the area was uninhabited. The first witnesses, 60 kilometers from the incident, reported an extraordinary luminosity and a sudden rise in temperature that burned some cabins and even the hair and clothes of several people. The detonation was heard more than 900 kilometers, with such force that crystal breakage was reported 650 kilometers from the site. The seismometers of the city of Ikustsk, 2,000 km to the south, registered an earthquake in a remote region called Tunguska.
The phenomenon was also felt on a global scale: two waves of atmospheric pressure circled the planet, and the high layers of the atmosphere lit up strangely for two months. In Moscow you could read the newspaper on moonless nights!
But the Tunguska event went unnoticed by scientists for 20 years, due to the enormous difficulties of access to such a remote region and the political turbulence of the Russia of that time. In 1927, the Russian geologist Leonid Kulik led the first scientific expedition to the site and noted the destruction of the forest, the absence of a crater and no trace of meteorite fragments. Magnetic tests, excavations and surveys in lakes and swamps failed to detect a single gram of a meteoric metal. So, what happened in Tunguska?
Was it a meteor?
Some very original explanations mention the collision of particles of matter with antimatter, a wandering black hole and even the accident of an alien spacecraft. Now it is known that the Tunguska explosion was an event necessarily produced by an object coming from outer space. If the impact had occurred only about eight hours earlier, the Russian city of St. Petersburg would have disappeared.
The aerial investigations began in 1935 and allowed to establish that, judging by the disposition of the rest of the forest, the catastrophe was produced by an explosion to about 7 km of height. The first estimations assured that the event had the force equivalent to 180 times the atomic bomb that devastated Hiroshima. According to the witnesses interviewed, the responsible object entered at an angle between 10 and 30 degrees above the horizon, and the fire tail of the fireball was 800 km long.
If the impact had occurred only about eight hours earlier, the Russian city of St. Petersburg would have disappeared.
There are several hypotheses that point to the person responsible for the event as a meteor, an asteroid fragment or a comet fragment. Simulations carried out show that a bolide object, between 5 and 100 meters in diameter, when entering the atmosphere is subjected by intense air pressure to the front and another almost non-existent in the rear. As a result of the difference in forces and temperatures, the object falls apart suddenly and violently.
In turn, the fragments are subjected to the same pressure difference and continue to be destroyed. All this happens in tenths of a second, so a solid object becomes a cloud of waste and, literally, an explosion in the air. And what produces the damage is the shock wave.
The mystery about the identity of the intruder still remains as to whether it contained ice, rock, iron or some other material; its degree of porosity, or what were its speed and its true angle of entry. Metallic meteorites are strong and dense and can fall almost intact. Then, the ideal object in Tunguska, for a NASA study group, would be a 50-meter stormy meteor whose explosion threw enough dust into the upper layers of the atmosphere to block out sunlight for several days.
However, Russians like the idea of the comet and do not like the idea of the asteroid. Recent simulations indicate that the object that ravaged Tunguska was smaller than estimated, which has serious implications, since such collisions would then be much more likely. The new theory indicates that the explosion generated a wave that was transported down at a speed greater than that of sound and took the form of a jet of high temperature gas that widened violently, knocking down trees and killing animals. This interpretation states that at the time of the collision, the forest was not in good health, so previous estimates exaggerated some aspects of the devastation.