The Tunguska event was a large explosion that occurred near the Stony Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908 (N.S.). The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 square kilometres (770 square miles) of forest yet caused no known human casualties. The explosion is generally attributed to the air burst of a meteoroid. It is classified as an impact event, even though no impact crater has been found; the object is thought to have disintegrated at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than to have hit the surface of the earth.
The Tunguska event is the largest impact event on earth in recorded history. Studies have yielded different estimates of the meteoroid's size, on the order of 60 to 190 metres (200 to 620 feet), depending on whether the body was a comet or a denser asteroid.
Since the 1908 event, there have been an estimated 1,000 scholarly papers (most in Russian) published on the Tunguska explosion. In 2013, a team of researchers published analysis results of micro-samples from a peat bog near the center of the affected area showing fragments that may be of meteoritic origin.
Early estimates of the energy of the air burst range from 10–15 megatons of TNT (42–63 petajoules) to 30 megatons of TNT (130 PJ), depending on the exact height of burst estimated when the scaling-laws from the effects of nuclear weapons are employed. However, modern supercomputer calculations that include the effect of the object's momentum find that more of the energy was focused downward than would be the case from a nuclear explosion and estimate that the airburst had an energy range from 3 to 5 megatons of TNT (13 to 21 PJ).
The 15-megaton (Mt) estimate represents an energy about 1,000 times greater than that of the atomic bomb dropped on Hiroshima, Japan - roughly equal to that of the United States' Castle Bravo (15.2 Mt) ground-based thermonuclear detonation on March 1, 1954, and about one-third that of the Soviet Union's Tsar Bomba explosion on October 30, 1961 (which, at 50 Mt, is the largest nuclear weapon ever detonated).
It is estimated that the Tunguska explosion knocked down some 80 million trees over an area of 2,150 km2 (830 sq mi), and that the shock wave from the blast would have measured 5.0 on the Richter magnitude scale. An explosion of this magnitude would be capable of destroying a large metropolitan area, but, due to the remoteness of the location, no human fatalities were officially documented. Several reports have indicated that two people may have died in the event; however, these deaths remain unofficial. This event has helped to spark discussion of asteroid impact avoidance.
Tunguska Event: Meteor that blasted millions of trees in Siberia only 'grazed' Earth, new research says Live Science - May 26, 2020
A new explanation for a massive blast over a remote Siberian forest in 1908 is even stranger than the mysterious incident itself. Known as the Tunguska event, the blast flattened more than 80 million trees in seconds, over an area spanning nearly 800 square miles (2,000 square kilometers) - but left no crater. A meteor that exploded before hitting the ground was thought by many to be the culprit. However, a comet or asteroid would likely have left behind rocky fragments after blowing up, and no "smoking gun" remnants of a cosmic visitor have ever been found.
UFO researchers have long claimed that the Tunguska event is the result of an exploding alien spaceship or even an alien weapon going off to save the Earth from an imminent threat. This hypothesis appears to originate from a science fiction story penned by Soviet engineer Alexander Kazantsev in 1946, in which a nuclear-powered Martian spaceship, seeking fresh water from Lake Baikal, blew up in mid-air. This story was inspired by Kazantsev's visit to Hiroshima in late 1945.
Many events in Kazantsev's tale were subsequently confused with the actual occurrences at Tunguska. The nuclear-powered UFO hypothesis was adopted by TV drama critics Thomas Atkins and John Baxter in their book The Fire Came By (1976). The 1998 television series The Secret KGB UFO Files (Phenomenon: The Lost Archives), broadcast on Turner Network Television, referred to the Tunguska event as "the Russian Roswell" and claimed that crashed UFO debris had been recovered from the site.
In 2004, a group from the Tunguska Space Phenomenon Public State Fund claimed to have found the wreck of an alien spacecraft at the site.
The proponents of the UFO hypothesis have never been able to provide significant evidence for their claims at east as far as we know. It should be noted that the Tunguska site is downrange from the Baikonur Cosmodrome and has been contaminated repeatedly by Russian space debris, most notably by the failed launch of the fifth Vostok test flight on December 22, 1960. The payload landed close to the Tunguska impact site, and a team of engineers was dispatched there to recover the capsule and its two canine passengers (which survived).
On 30 June 1908, at around 07:17 local time, Evenki natives and Russian settlers in the hills north-west of Lake Baikal observed a column of bluish light, nearly as bright as the Sun, moving across the sky. About ten minutes later, there was a flash and a sound similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away. The majority of witnesses reported only the sounds and tremors, and did not report seeing the explosion. Eyewitness accounts vary regarding the sequence and duration of the events.
The explosion registered at seismic stations across Eurasia. It is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on the Richter magnitude scale. It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain. Over the next few days, night skies in Asia and Europe were aglow; it has been theorized that this was due to light passing through high-altitude ice particles that had formed at extremely low temperatures—a phenomenon that many years later would be produced by space shuttles. In the United States, the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a months-long decrease in atmospheric transparency due to an increase in suspended dust particles.
The first recorded expedition arrived at the scene more than a decade after the event. In 1921, the Russian mineralogist Leonid Kulik, visiting the Podkamennaya Tunguska River basin as part of a survey for the Soviet Academy of Sciences, deduced from local accounts that the explosion had been caused by a giant meteorite impact. He persuaded the Soviet government to fund an expedition to the Tunguska region, based on the prospect of meteoric iron that could be salvaged to aid Soviet industry. Kulik's party eventually undertook an expedition in 1927.
Upon arrival, Kulik made arrangements with the local Evenki hunters to guide his party to the impact site. Reaching the explosion site was an extremely arduous task. Upon reaching an area just south of the site, the superstitious Evenki hunters would go no farther, fearing what they called the Valleymen. Kulik had to return to the nearby village, and his party was delayed for several days while they sought new guides.
The spectacle that confronted Kulik as he stood on a ridge overlooking the devastated area was overwhelming. To the explorers' surprise, they found no crater. There was instead around ground zero a zone 8 kilometres (5.0 miles) across of trees scorched and devoid of branches, but standing upright. The trees farther away had been partly scorched and knocked down in a direction away from the centre. Much later, in the 1960s, it was established that the zone of leveled forest occupied an area of 2,150 km2 (830 sq mi), its shape resembling a gigantic spread-eagled butterfly with a "wingspan" of 70 km (43 mi) and a "body length" of 55 km (34 mi). Upon closer examination, Kulik located holes that he erroneously concluded were meteorite holes; he did not have the means at that time to excavate the holes.
During the next ten years there were three more expeditions to the area. Kulik found several dozens of little "pothole" bogs, each some 10 to 50 metres (33 to 164 feet) in diameter, that he thought might be meteoric craters. After a laborious exercise in draining one of these bogs (the so-called "Suslov's crater", 32 m (105 ft) in diameter), he found an old stump on the bottom, ruling out the possibility that it was a meteoric crater. In 1938, Kulik arranged for an aerial photographic survey of the area covering the central part of the leveled forest (250 square kilometres (97 sq mi)). The negatives of these aerial photographs (1,500 negatives, each 18 by 18 centimetres (7.1 by 7.1 inches)) were burned in 1975 by order of Yevgeny Krinov, then Chairman of the Committee on Meteorites of the USSR Academy of Sciences, as part of an initiative to dispose of hazardous nitrate film. Positive prints were preserved for further study in the Russian city of Tomsk.
Expeditions sent to the area in the 1950s and 1960s found microscopic silicate and magnetite spheres in siftings of the soil. Similar spheres were predicted to exist in the felled trees, although they could not be detected by contemporary means. Later expeditions did identify such spheres in the resin of the trees. Chemical analysis showed that the spheres contained high proportions of nickel relative to iron, which is also found in meteorites, leading to the conclusion they were of extraterrestrial origin. The concentration of the spheres in different regions of the soil was also found to be consistent with the expected distribution of debris from a meteoroid air burst. Later studies of the spheres found unusual ratios of numerous other metals relative to the surrounding environment, which was taken as further evidence of their extraterrestrial origin.
Chemical analysis of peat bogs from the area also revealed numerous anomalies considered consistent with an impact event. The isotopic signatures of stable carbon, hydrogen, and nitrogen isotopes at the layer of the bogs corresponding to 1908 were found to be inconsistent with the isotopic ratios measured in the adjacent layers, and this abnormality was not found in bogs located outside the area. The region of the bogs showing these anomalous signatures also contains an unusually high proportion of iridium, similar to the iridium layer found in the Cretaceous-Paleogene boundary. These unusual proportions are believed to result from debris from the falling body that deposited in the bogs. The nitrogen is believed to have been deposited as acid rain, a suspected fallout from the explosion.
Researcher John Anfinogenov has suggested that a boulder found at the event site, known as John's stone, is a remnant of the meteorite.
Testimony of S. Semenov, as recorded by Leonid Kulik's expedition in 1930.
"At breakfast time I was sitting by the house at Vanavara trading post (65 kilometres/40 miles south of the explosion), facing North. I suddenly saw that directly to the North, over Onkoul's Tunguska road, the sky split in two and fire appeared high and wide over the forest (as Semenov showed, about 50 degrees up - expedition note). The split in the sky grew larger, and the entire Northern side was covered with fire. At that moment I became so hot that I couldn't bear it, as if my shirt was on fire; from the northern side, where the fire was, came strong heat. I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, and I was thrown a few yards. I lost my senses for a moment, but then my wife ran out and led me to the house. After that such noise came, as if rocks were falling or cannons were firing, the earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it. When the sky opened up, hot wind raced between the houses, like from cannons, which left traces in the ground like pathways, and it damaged some crops. Later we saw that many windows were shattered, and in the barn a part of the iron lock snapped."
Testimony of Chuchan of Shanyagir tribe, as recorded by I.M.Suslov in 1926.
"We had a hut by the river with my brother Chekaren. We were sleeping. Suddenly we both woke up at the same time. Somebody shoved us. We heard whistling and felt strong wind. Chekaren said, 'Can you hear all those birds flying overhead?' We were both in the hut, couldn't see what was going on outside. Suddenly, I got shoved again, this time so hard I fell into the fire. I got scared. Chekaren got scared too. We started crying out for father, mother, brother, but no one answered. There was noise beyond the hut, we could hear trees falling down. Me and Chekaren got out of our sleeping bags and wanted to run out, but then the thunder struck. This was the first thunder. The Earth began to move and rock, wind hit our hut and knocked it over. My body was pushed down by sticks, but my head was in the clear. Then I saw a wonder: trees were falling, the branches were on fire, it became mighty bright, how can I say this, as if there was a second sun, my eyes were hurting, I even closed them. It was like what the Russians call lightning. And immediately there was a loud thunderclap. This was the second thunder. The morning was sunny, there were no clouds, our Sun was shining brightly as usual, and suddenly there came a second one!
"Me and Chekaren had some difficulty getting under from the remains of our hut. Then we saw that above, but in a different place, there was another flash, and loud thunder came. This was the third thunder strike. Wind came again, knocked us off our feet, struck against the fallen trees.
"We looked at the fallen trees, watched the tree tops get snapped off, watched the fires. Suddenly Chekaren yelled 'Look up' and pointed with his hand. I looked there and saw another flash, and it made another thunder. But the noise was less than before. This was the fourth strike, like normal thunder.
"Now I remember well there was also one more thunder strike, but it was small, and somewhere far away, where the Sun goes to sleep."
Sibir newspaper, July 2, 1908
"On the 17th of June, around 9 in the AM, we observed an unusual natural occurrence. In the N Karelinski village (200 verst N of Kirensk) the peasants saw to the North-West, rather high above the horizon, some strangely bright (impossible to look at) bluish-white heavenly body, which for 10 minutes moved downwards. The body appeared as a "pipe", i.e. a cylinder. The sky was cloudless, only a small dark cloud was observed in the general direction of the bright body. It was hot and dry. As the body neared the ground (forest), the bright body seemed to smudge, and then turned into a giant billow of black smoke, and a loud knocking (not thunder) was heard, as if large stones were falling, or artillery was fired. All buildings shook. At the same time the cloud began emitting flames of uncertain shapes. All villagers were stricken with panic and took to the streets, women cried, thinking it was the end of the world. "The author of these lines was meantime in the forest about 6 verst N of Kirensk, and heard to the NE some kind of artillery barrage, that repeated in intervals of 15 minutes at least 10 times. In Kirensk in a few buildings in the walls facing north-east window glass shook."
Siberian Life newspaper, July 27, 1908
"When the meteorite fell, strong tremors in the ground were observed, and near the Lovat village of the Kansk uezd two strong explosions were heard, as if from large-caliber artillery."
Krasnoyaretz newspaper, July 13, 1908
"Kezhemskoe village. On the 17th an unusual atmospheric event was observed. At 7:43 the noise akin to a strong wind was heard. Immediately afterwards a horrific thump sounded, followed by an earthquake which literally shook the buildings, as if they were hit by a large log or a heavy rock. The first thump was followed by a second, and then a third. Then - the interval between the first and the third thumps were accompanied by an unusual underground rattle, similar to a railway upon which dozens of trains are traveling at the same time. Afterwards for 5 to 6 minutes an exact likeness of artillery fire was heard: 50 to 60 salvoes in short, equal intervals, which got progressively weaker. After 1.5 - 2 minutes after one of the "barrages" six more thumps were heard, like cannon firing, but individual, loud, and accompanied by tremors. "The sky, at the first sight, appeared to be clear. There was no wind and no clouds. However upon closer inspection to the North, i.e. where most of the thumps were heard, a kind of an ashen cloud was seen near the horizon which kept getting smaller and more transparent, and possibly by around 2-3 p.m. completely disappeared."
There was little scientific curiosity about the impact at the time, possibly owing to the isolation of the Tunguska region. If there were any early expeditions to the site, the records were lost during the subsequent chaotic years - World War I, the Russian Revolution of 1917, and the Russian Civil War.
The first recorded expedition arrived at the scene more than a decade after the event. In 1921, the Russian mineralogist Leonid Kulik, visiting the Podkamennaya Tunguska River basin as part of a survey for the Soviet Academy of Sciences, deduced from local accounts that the explosion had been caused by a giant meteorite impact. He persuaded the Soviet government to fund an expedition to the Tunguska region, based on the prospect of meteoritic iron that could be salvaged to aid Soviet industry.
Kulik's party reached the site in 1927. To their surprise, no crater was to be found. There was instead a region of scorched trees about 50 kilometres (30 mi) across. A few near ground zero were still strangely standing upright, their branches and bark stripped off. Those farther away had been knocked down in a direction away from the center.
During the next ten years there were three more expeditions to the area. Kulik found a little "pothole" bog that he thought might be the crater, but after a laborious exercise in draining the bog, he found there were old stumps on the bottom, ruling out the possibility that it was a crater. In 1938, Kulik managed to arrange for an aerial photographic survey of the area, which revealed that the event had knocked over trees in a huge butterfly-shaped pattern. Despite the large amount of devastation, there was no crater to be seen. Expeditions sent to the area in the 1950s and 1960s found microscopic glass spheres in siftings of the soil. Chemical analysis showed that the spheres contained high proportions of nickel and iridium, which are found in high concentrations in meteorites, hinting that they were of extraterrestrial origin.
Detailed systematic eyewitness reports began to be gathered as late as 1959, when interviews were conducted with many of the indigenous people who had been within 100 kilometres (60 mi) of the explosion. Most of these accounts claimed that the local people had been covered with boils after the explosion, with whole families dying off. The medical scientists attached to the expedition concluded that there had been an epidemic of smallpox in the area at the time. Expeditions led by Gennady Plekhanov found no elevated levels of radiation, which would have been expected had the detonation been nuclear in nature.
In scientific circles, the leading explanation for the explosion is the airburst of a meteoroid 6 to 10 kilometers (4-6 mi) above the Earth's surface. Meteoroids enter the Earth's atmosphere from outer space every day, usually travelling at a speed of more than 10 kilometers per second (6 mi/sec). Most are small but occasionally a larger one enters from space. The heat generated by compression of air in front of the body (ram pressure) as it travels through the atmosphere is immense and most meteoroids burn up or explode before they reach the ground. Starting from the second half of the 20th century, close monitoring of the Earth's atmosphere has led to the discovery that such meteoroid airbursts occur rather frequently. A stony meteoroid of about 10 meters (30 ft) in diameter can produce an explosion of around 20 kilotons, similar to that of the Little Boy bomb dropped on Hiroshima, and data released by the U.S. Air Force's Defense Support Program indicate that such explosions occur high in the upper atmosphere more than once a year. Tunguska-like megaton-range events are much more rare. Eugene Shoemaker estimated that such events occur about once every 300 years.
The curious effect of the Tunguska explosion on the trees near ground zero was replicated during atmospheric nuclear tests in the 1950s and 1960s. These effects are caused by the shock wave produced by large explosions. The trees directly below the explosion are stripped as the blast wave moves vertically downward, while trees further away are felled because the blast wave is travelling closer to the horizontal when it reaches them.
Soviet experiments performed in the mid-1960s, with model forests (made of matches) and small explosive charges slid downward on wires, produced butterfly-shaped blast patterns strikingly similar to the pattern found at the Tunguska site. The experiments suggested that the object had approached at an angle of roughly 30 degrees from the ground and 115 degrees from north and had exploded in mid-air.
Asteroid or Comet
The composition of the Tunguska body remains a matter of controversy.
In 1930, the British astronomer F.J.W. Whipple suggested that the Tunguska body was a small comet. A cometary meteorite, being composed primarily of ice and dust, could have been completely vaporized by the impact with the Earth's atmosphere, leaving no obvious traces. The comet hypothesis was further supported by the glowing skies (or "skyglows" or "bright nights") observed across Europe for several evenings after the impact, apparently caused by dust that had been dispersed across the upper atmosphere.
In 1978, Slovak astronomer Lubor Kresak suggested that the body was a piece of the short-period Comet Encke, which is responsible for the Beta Taurid meteor shower; the Tunguska event coincided with a peak in that shower. It is now known that bodies of this kind explode at frequent intervals tens to hundreds of kilometres above the ground. Military satellites have been observing these explosions for decades.
In 1983, astronomer Zdenek Sekanina published a paper criticizing the comet hypothesis. He pointed out that a body composed of cometary material, traveling through the atmosphere along such a shallow trajectory, ought to have disintegrated, whereas the Tunguska body apparently remained intact into the lower atmosphere. Sekanina argued that the evidence pointed to a dense, rocky object, probably of asteroidal origin.
This hypothesis was further boosted in 2001, when Farinella, Foschini, et al. released a study suggesting that the object had arrived from the direction of the asteroid belt.
Proponents of the comet hypothesis have suggested that the object was an extinct comet with a stony mantle that allowed it to penetrate the atmosphere.
The chief difficulty in the asteroid hypothesis is that a stony object should have produced a large crater where it struck the ground, but no such crater has been found. It has been hypothesized that the passage of the asteroid through the atmosphere caused pressures and temperatures to build up to a point where the asteroid abruptly disintegrated in a huge explosion. The destruction would have to have been so complete that no remnants of substantial size survived, and the material scattered into the upper atmosphere during the explosion would have caused the skyglows.
Models published in 1993 suggested that the stony body would have been about 60 metres across, with physical properties somewhere between an ordinary chondrite and a carbonaceous chondrite.
Christopher Chyba and others have proposed a process whereby a stony meteorite could have exhibited the behavior of the Tunguska impactor. Their models show that when the forces opposing a body's descent become greater than the cohesive force holding it together, it blows apart, releasing nearly all its energy at once. The result is no crater, and damage distributed over a fairly wide radius, all of the damage being blast and thermal.
High levels of carbon that doesn't form on Earth found in peat bogs suggest a comet, which have high amounts of carbon compared to most asteroids, was the cause of the Tunguska event; however, it is not impossible for asteroids to contain the carbon necessary to result in the heightened levels of carbon in the peat bogs in 1908.
During the 1990s, Italian researchers extracted resin from the core of the trees in the area of impact, to examine trapped particles that were present during the 1908 event. They found high levels material commonly found in rocky asteroids and rarely found in comets.
Today, most Russian scientists believe the Tunguska event was the result of a comet, while most American scientists take the belief that it was some sort of asteroid.
In June of 2007 it was announced that scientists from the University of Bologna had identified a lake in the Tunguska region as a possible impact crater from the event. Lake Cheko is a small bowl shaped lake approximately 8 kilometers north-north-west of the epicenter. The hypothesis has been challenged by other impact crater specialists. A 1961 investigation had dismissed a modern origin of Lake Cheko, saying that the presence of meters thick silt deposits at the lake's bed suggests an age of at least 5000 years.
Scientific understanding of the behaviour of meteorites in the Earth's atmosphere was much sparser during the early decades of the 20th century. Due to this lack of knowledge, as well as a paucity of scientific data about Tunguska due to Soviet secrecy during the Cold War, a great many other hypotheses for the Tunguska event have sprung up, with varying degrees of credibility.
In 1989, the astronomers D'Alessio and Harms suggested that some of the deuterium in a comet entering the Earth's atmosphere may have undergone a nuclear fusion reaction, leaving a distinctive signature in form of carbon-14. They concluded that the release of nuclear energy may have been almost negligible. Independently, in 1990, César Sirvent proposed that a deuterium comet, i.e., a comet with an anomalous high concentration of deuterium into its composition, may have exploded as a natural hydrogen bomb, generating most of the energy released. The sequence would be first a mechanical or kinetic explosion, and instants later a thermonuclear reaction generated by this first explosion. This hypothesis would explain the inconsistences related to an unusual high ratio of electromagnetic energy / kinetic energy and cited in the famous paper by Cowan, Atluri, and Libby published in Nature. It is, however, inconsistent with knowledge both of the composition of comets and of the temperature and pressure conditions necessary for initiating a nuclear fusion reaction.
In 1973, Albert A. Jackson IV and Michael P. Ryan, Jr., physicists at the University of Texas, proposed that the Tunguska event was caused by a "small" (around 1020 g to 1022 g) black hole passing through the Earth. Unfortunately for this hypothesis, there is no evidence for a second explosion occurring as the black hole exited the Earth and it has not gained wide acceptance. Furthermore, Stephen Hawking's subsequent hypothesis that black holes radiate energy via Hawking radiation indicates that such a small black hole would have evaporated away long before it could encounter the Earth.
In 1965, Cowan, Atluri, and Libby suggested that the Tunguska event was caused by the annihilation of a chunk of antimatter falling from space. However, as with the other hypotheses described in this section, this does not account for the mineral debris left in the area of the explosion. Furthermore, there is no astronomical evidence for the existence of such chunks of antimatter in our region of the universe. If such objects existed, they should be constantly producing energetic gamma rays due to annihilation against the interstellar medium, but such gamma rays have not been observed.
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