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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 around 7:14 a.m. (0:14 UT, 7:02 a.m. local solar time) on June 30, 1908 (June 17 in the Julian calendar, in use locally at the time). The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3–6 miles) above Earth's surface. Different studies have yielded varying estimates for the object's size, with general agreement that it was a few tens of metres across. Although the meteor or comet air burst rather than directly hitting the surface, this event is still referred to as an impact. Estimates of the energy of the blast range from 5 megatons to as high as 30 megatons[5] of TNT, with 10–15 megatons the most likely - about 1000 times as powerful as the bomb dropped on Hiroshima, Japan and about one third the power of Tsar Bomba. The explosion knocked over an estimated 80 million trees over 2,150 square kilometres (830 square miles). The earthquake from the blast measured 5.0 on the Richter scale. An explosion of this magnitude is capable of destroying a large metropolitan area. This possibility has helped to spark discussion of asteroid deflection strategies. The Tunguska event is believed to be the largest impact event on land in Earth's recent history; impacts of similar size in remote ocean areas would have gone unnoticed before the advent of global satellite monitoring in the 1960s and 1970s.
The most recent major encounter between Earth and what may have been an asteroid was a 1908 explosion in the atmosphere above the Tunguska region of Siberia. The force of the blast flattened more than 200,000 hectares (500,000 acres) of pine forest and killed thousands of reindeer. The number of human casualties, if any, is unknown. The first scientific expedition went to the region two decades later. This expedition and several detailed studies following it found no evidence of an impact crater. This led scientists to believe that the heat generated by friction with the atmosphere as the object plunged toward Earth was great enough to make the object explode before it hit the ground.
If the Tunguska object had exploded in a less remote area, the loss of human life and property could have been astounding. Military satellites—in orbit around Earth watching for explosions that could signal violations of weapons testing treaties—have detected dozens of smaller asteroid explosions in the atmosphere each year. In 1995 NASA, the Jet Propulsion Laboratory, and the U.S. Air Force began a project called Near-Earth Asteroid Tracking (NEAT). NEAT uses an observatory in Hawaii to search for asteroids with orbits that might pose a threat to Earth. By tracking these asteroids, scientists can calculate the asteroids’ precise orbits and project these orbits into the future to determine whether the asteroids will come close to Earth.
MosNews-Scientists from the Siberian city of Krasnoyarsk claim that they have discovered several artifacts with extraterrestrial writings near the fall site of the Tunguska meteorite, the Regnum news agency reports. The president of the Tunguska Space Phenomenon research foundation told reporters that several quartz boulders with mysterious writings on them were found in the Tunguska river basin in 2006. The boulders were tested in Krasnoyarsk and Moscow and test results speak for the fact that they are of extraterrestrial origin, he said. The boulders were covered in strange signs of artificial origin, presumably made with plasma. Russian researchers suggested a hypothesis that the quartz tablets were parts of an information container delivered to Earth by the extraterrestrial spaceship that crashed in Tunguska region in 1908. Russian researcher also said that scientists from the United States, Britain, France and Germany have requested the newly-found artifacts for research, but Russians want to be the first people to decode the message from another civilization.
Siberia believed to be site of largest meteor impact on Earth
July 3, 1998
Web posted at: 10:03 p.m. EDT (0203 GMT)
MOSCOW (CNN) -- On June 30, 1908, an enormous fireball crashed to the ground in the remote Siberian region of Tunguska, destroying a huge swath of ancient growth forest. Russian scientists believe this was the largest meteorite to fall to Earth in the past 2,000 years. "A majority of scientists lean toward the theory that it was a collision from a large interplanetary body," said Professor Valeri Shuvalov of the Russian Institute of Geosphere Dynamics. But the scientists have so far been unable to explain why the huge interplanetary body did not leave any fragments behind. The only people to see the massive explosion were the Evenki people, reindeer herders indigenous to Siberia. They believed the explosion was caused by a revengeful "lord of thunder." Regardless, researchers are hoping that the Tunguska event can help them better prepare for future meteor collisions. Scientists have charted about 500 meteors near the Earth's orbit and estimate that 100 of those are potentially dangerous. Some scientific ideas to prevent a catastrophic crash sound much more like something out of a Hollywood movie script. Says astrophysicist Mikhail Smirnov of the Russian Institute of Astronomy: "If we know at least 15 years in advance that an asteroid will impact with Earth, then we could send an expedition up to it and redirect its course with the help of a controlled atomic explosion."
(from: CNN and Reuters)
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