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In the early morning of June 30, 1908, something exploded over Siberia. The event shattered the normal stillness of the sparsely populated taiga, so powerful that it crushed an area of forest 2,150 square kilometers (830 square miles) in size, cutting down approximately 80 million trees.
Eyewitness reports describe a bright ball of light, broken windows and fallen plaster, and a deafening detonation not far from the local river. The Tunguska event, as it became known, was later characterized as an explosive, or bolide, meteorite of up to 30 megatons, at an altitude of 10 to 15 kilometers (6.2 to 9.3 miles).
It is often referred to as the “greatest impact event in recorded history”, although no impact crater was found. Subsequent searches have found rock fragments that could be of meteoric origin, but the event still has an impending question mark. Was it really a fireball? And if it were not, what could it be?
Well, we may never know … but according to a recent peer-reviewed article, a large iron asteroid that enters Earth’s atmosphere and skims the planet at a relatively low altitude before flying back into space It could have produced the effects of the Tunguska event by producing a shock wave that devastated the surface.
“We have studied the conditions of passage of asteroids with diameters of 200, 100 and 50 meters, which consist of three types of materials: iron, stone and water ice, through the Earth’s atmosphere with a minimum altitude of trajectory in the 10 to 15 kilometer range, “wrote researchers led by astronomer Daniil Khrennikov of the Federal University of Siberia in his article.
“The results obtained support our idea to explain one of astronomy’s long-standing problems: the Tunguska phenomenon, which has not received reasonable and exhaustive interpretations to date. We argue that the Tunguska event was caused by an iron asteroid body , which passed Earth’s atmosphere and continued into near-solar orbit. “
The team mathematically modeled the pitch of the three asteroid compositions in different sizes to determine if such an event is possible.
The ice body, a hypothesis put forward by Russian researchers in the 1970s, was fairly simple to dismiss. The heat generated by the velocity required to obtain the estimated trajectory would have completely melted the ice body before it reached the distance that the observation data suggests it covered.
The rocky body would also be less likely to survive. Meteorites are believed to explode when air enters the body through small fractures in the meteorite, causing a build-up of pressure as it flies through the air at high speed. Iron bodies are much more resistant to fragmentation than rocky ones.
According to the team’s calculations, the most likely culprit is an iron meteorite 320 to 650 feet (100 to 200 meters) wide that flew 3,000 kilometers (1,800 miles) through the atmosphere. It would never have dropped below 11.2 kilometers per second (7 mps), or below an altitude of 11 kilometers.
This model would explain various characteristics of the Tunguska event. The lack of an impact crater, for example, since the meteorite would skim the epicenter of the explosion without falling.
The lack of iron debris is also explained by this high speed, since the object would move too fast and would be too hot to fall too much. The researchers said that any lost mass would be produced by sublimation of individual iron atoms, which would look exactly like normal terrestrial oxides.
“Within this version,” the researchers noted, “we can explain the optical effects associated with strong dust from upper layers of the atmosphere on Europe, which caused a brilliant glow from the night sky.”
While the results are certainly compelling, the researchers point out that their document has some limitations that they hope can be resolved with future research. On the one hand, “they did not address the problem of shock wave formation,” although their initial comparisons with the Chelyabinsk meteorite allowed a large shock wave to plausibly occur in Tunguska.
However, the idea of an iron body hitting our atmosphere is certainly intriguing, and we can look forward to more articles on the subject.
The research has been published in the Monthly notices from the Royal Astronomical Society.
