tailieunhanh - COMET AND ASTEROID RISK: AN ANALYSIS OF THE 1908 TUNGUSKA EVENT

Early in the morning on June 30, 1908, a giant airburst occurred over the basin of the Podkamennaya Tunguska River in Central Siberia, Russia, leveling trees over an area of 2,000 km2 (770 mi2) (Figure 1). Eyewitnesses described a ―fire ball, bright as the Sun‖ (Longo, 2007). The event produced seismic and pressure waves that were recorded all over the world and led to atmospheric phenomena (. , bright nights, noctilucent clouds) observed over much of Eurasia. The released energy was later estimated to be equivalent to a 10 megaton (Mton) TNT explosion, about 1,000 times as powerful as the nuclear bomb dropped over Hiroshima. | COMET AND ASTEROID RISK AN ANALYSIS OF THE 1908 TUNGUSKA EVENT RMS Special Report INTRODUCTION Early in the morning on June 30 1908 a giant airburst occurred over the basin of the Podkamennaya Tunguska River in Central Siberia Russia leveling trees over an area of 2 000 km2 770 mi2 Figure 1 . Eyewitnesses described a fire ball bright as the Sun Longo 2007 . The event produced seismic and pressure waves that were recorded all over the world and led to atmospheric phenomena . bright nights noctilucent clouds observed over much of Eurasia. The released energy was later estimated to be equivalent to a 10 megaton Mton TNT explosion about 1 000 times as powerful as the nuclear bomb dropped over Hiroshima in 1945. Although the origin of this phenomenon has been widely debated for the past century it is now generally accepted that the blast was due to the explosion of a comet or an asteroid in the lower atmosphere occurring at a height of 5 to 10 km 3 to 6 mi over the remote Siberian forest and measuring approximately 50 m 164 ft in diameter Longo 2007 and http tunguska . Figure 1 Felled trees in the Tunguska impact area in Russia following an explosion of an asteroid or a comet in the atmosphere on June 30 1908 about 80 million trees were leveled by the blast Source Soviet Academy of Science 1927expedition led by Leonid Kulik Due to the remote impact location this disaster did not cause any significant damage to human settlements. However the occurrence of a Tunguska-type event over a populated region would constitute a major catastrophe. This report begins with a discussion of the risk associated with extraterrestrial bodies orbiting the sun including comets and asteroids which can become meteors and meteorites hitting the Earth s atmosphere and surface respectively. Examples of small and moderate-sized impact events in recent history are detailed. A Tunguska-type footprint is also developed based on the available information from felled trees and .