On the early morning of June 30, 1908, an explosion estimated at a thousand times more powerful than the atomic bomb dropped on Hiroshima, occurred over a remote region of Siberia near the Podkamennaya Tunguska river, flattening an area of the taiga forest 2,150 square kilometres in size and felling 80 million trees.
Eyewitness reports describe a brilliant ball of light and a “hot wind (that) raced between the houses, like from cannons, which left traces in the ground like pathways,” damaging crops, upturning anything in its path, shattering windows and smashing plaster.
Because the area was so remote, it’s believed only a few people were killed. Had it happened over a populated area, the destruction would have been unthinkable.
The explosion registered at seismic stations across Eurasia, and air waves from the blast were detected in Germany, Denmark, Croatia, the United Kingdom, and as far away as Washington, D.C.
The mysterious Tunguska event — as it came to be known — was later characterized as an exploding meteor, or bolide, up to 30 megatons, at an estimated altitude of 10 to 15 kilometres (6.2 to 9.3 miles), Science Alert reported.
Later searches have turned up fragments of rock that could be meteoric in origin, but the event still has a looming question mark. Was it really a meteor? And if it not, what could it be? Was it a UFO?
It’s possible we’ll never actually know… but according to a recent peer-reviewed paper, a large iron asteroid entering Earth’s atmosphere and skimming the planet at a relatively low altitude before flying back into space could have produced the effects of the Tunguska event by producing a shock wave that devastated the surface, Science Alert reported.
“We have studied the conditions of through passage of asteroids with diameters 200, 100, and 50 metres, consisting of three types of materials — iron, stone, and water ice, across the Earth’s atmosphere with a minimum trajectory altitude in the range 10 to 15 kilometres,” wrote researchers led by astronomer Daniil Khrennikov of the Siberian Federal University in their paper.
“The results obtained support our idea explaining one of the long-standing problems of astronomy — the Tunguska phenomenon, which has not received reasonable and comprehensive interpretations to date. We argue that the Tunguska event was caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued to the near-solar orbit.”
The team mathematically modelled the passage of all three asteroid compositions at different sizes to determine whether such an event is possible, Science Alert reported.
The ice body — a hypothesis floated by Russian researchers in the 1970s — was pretty simple to rule out. The heat generated by the speed required to obtain the estimated trajectory would have entirely melted the ice body before it reached the distance observational data suggests it covered.
The rocky body, too, would be less likely to survive. Meteors are thought to explode when air enters the body through small fractures in the meteor, 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, Science Alert reported.
According to the team’s calculations, the most likely culprit is an iron meteorite between 100 and 200 metres (320 to 650 feet) across that flew 3,000 kilometres (1,800 miles) through the atmosphere. It would never have dropped below 11.2 kilometres per second (7 mps), or below an altitude of 11 kilometres.
This model would explain several characteristics of the Tunguska event. The lack of an impact crater, for one, since the meteor would skim past the epicentre of the explosion without falling, Science Alert reported.
The lack of iron debris is also explained by this high velocity, since the object would be moving too fast, and would be too hot, to drop much. Any mass lost would be, the researchers said, through the sublimation of individual iron atoms, which would look exactly like normal terrestrial oxides.
“Within this version,” the researchers also noted, “we can explain optical effects associated with a strong dustiness of high layers of the atmosphere over Europe, which caused a bright glow of the night sky.”
According to The National Interest, Dr. Sergei Karpov, of the Kirensky Physics Institute, said this particular iron-asteroid theory could answer some important questions.
“At present, there are over 100 hypotheses about the nature of the Tunguska phenomenon,” he told The Siberian Times.
“They include the fall of a small asteroid measuring several dozen meters, consisting of typical asteroid materials, either metal or stone, as well as ice. We calculated trajectory characteristics of space from 50 to 200 meters in diameter, and our modeling shows that it could not consist of rock or ice because, in contrast with iron, such bodies fall apart quickly because of colossal aerodynamic pressure in the atmosphere.”
There have been several other theories proposed for the Tunguska event, The National Interest reported.
One cites Nikola Tesla’s experiments with wireless transmission that may have inadvertently caused the explosion. And there is always the speculation that the explosion was caused by a UFO.
The research was published in the Monthly Notices of the Royal Astronomical Society.