The Tunguska Event, sometimes called the Tunguska explosion, was a massive explosion that occurred near the Podkamennaya (Lower Stony) Tunguska River in what is now Krasnoyarsk Krai of Russia, at 7:40 a.m. on June 30, 1908 Julian (July 13 Gregorian).
The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 5-10 kilometers (3-6 miles) above Earth’s surface. Different studies yielded varying estimates for the meteor’s size, including 30 meters, 50 metres, 60 metres, 90 to 190 metres, and up to 1200 metres in diameter. Although the meteor or comet is considered to have burst prior to hitting the surface, this event is still referred to as an impact event. Estimates on the energy of the blast include 3-5 megatons and as high as 30 megatons of TNT. 10-15 megatons has been considered the most likely to be accurate - about 1,000 times more powerful than the bomb dropped on Hiroshima, Japan. The explosion felled an estimated 80 million trees over 2,150 square kilometers (830 square miles). It is estimated to have measured 5.0 on the Richter scale.
The Tunguska event is the largest impact event in recent history. An explosion of this magnitude had the potential to devastate large metropolitan areas had it occurred over a large city. This possibility has helped to spark discussion of asteroid deflection strategies.
Speculative hypotheses:-
Natural H-bomb
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 the 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.
Black hole
In 1973, Albert A. Jackson and Michael P. Ryan, physicists at the University of Texas, proposed that the Tunguska event was caused by a “small” (around 10E20 g to 10E22 g) black hole passing through the Earth. Unfortunately for this hypothesis, there is no evidence for a so-called “exit event” - a second explosion occurring as the black hole, having tunneled through the Earth, shot out the other side on its way back into space - and it has not gained acceptance in the scientific community. This hypothesis was used by Larry Niven in his science fiction story The Borderland of Sol.
Antimatter
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.
UFO crash
UFO aficionados 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 any significant evidence for their claims. 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).