Asteroid Comet Impact Hazards - Florida International University

The Sky Has Split Apart - The Cosmic Mystery of the Century
What has been learned since the first organized investigation in 1927? And what is the current thinking?
To this day the vast Tunguska region remains a desolate area of mosquito-infested bogs and swamps
amid the beautiful hilly taiga. To reach the epicenter you are dropped off by helicopter. Or you hike in.
For a trained eye, evidence of the blast is not difficult to identify, even after 90 years. The power of the
blast felled trees outward in a radial pattern over an area of 2,1504 square kilometers, more than half the
size of Rhode Island. In the hot central region of the epicenter the forest flashed into an ascending
column of flame visible several hundred kilometers away.
The fires burned for weeks, destroying an area of 1,000 square kilometers. Ash and powdered tundra
fragments sucked skyward by the fiery vortex were caught up in the global air circulation and carried
around the world. Meanwhile, bursts of thunder echoed across the land to a distance of some 800
kilometers.5
The mass of the object has been estimated at about 100,000 tons and the force of the explosion at 40
megatons of TNT, 2,000 times the force of the atomic bomb exploded over Hiroshima in 1945. (By
comparison, the explosive force of the Arizona asteroid that struck some 50,000 years ago, has been
estimated at 3.5 megatons.6)
Following the Tunguska explosion, unusually colorful sunsets and sunrises caught the world's attention
and were reported from many countries, including Western Europe, Scandinavia, Russia, and Western
Siberia. The climax of visual displays occurred on the night of June 30th. Although they continued, they
weakened exponentially over several weeks until they died away.
The New York Times of July 3, 1908 reported "remarkable lights" being "observed in the northern
heavens on Tuesday and Wednesday nights." Scientists mistakenly attributed the dazzling displays to
solar outbursts causing electrical disturbances in the atmosphere. Similar light displays had been
reported in 1883 at the time of the Krakatoa volcanic explosion in the Sunda Strait, said the Times.
These "optical fireworks" and "light nights" were most prominent over Eastern Siberia and Middle Asia.
They included a night sky bright enough to read a watch or newspaper by. Dust in the air at heights of
from 40 to 70 kilometers caused high-altitude noctiluscent, or "night-shining," clouds that illuminated
much of the visible sky. And there were halos around the Sun. A marked decrease of the air's
transparency was recorded in the United States by the Smithsonian Astrophysical Observatory and
California's Mount Wilson Observatory.
Disturbances in earth's magnetic field were reported 900 kilometers southeast of the epicenter by the
Irkutsk Observatory. These were magnetic "storms" similar to the ones produced by nuclear test
explosions in the atmosphere. The seismograph station some 4,000 kilometers west in St. Petersburg
recorded tremors produced by the blast, as did more distant stations around the world.
http://www.galisteo.com/tunguska/docs/splitsky.html (2 of 6)12/5/2005 4:30:58 PM