The most likely cause of the explosion was the entry into the atmosphere of a piece of a comet which would have produced a large fireball and blast wave. Since a comet is composed primarily of ice, the fragment would have melted during its passage through the Earth's atmosphere, leaving no impact crater and no debris. Since the Tunguska Event coincided with the Earth's passage through the orbit of Comet Encke, the explosion could have been caused by a piece of that comet.
A Meteor's Journey to Earth
A meteoroid moving through outer space may pass close enough to the Earth to be trapped by the planet's gravitational field. If this happens, the meteoroid is drawn into the atmosphere and toward the Earth's surface by the force of gravity.
When a meteoroid enters the atmosphere, it is traveling at a tremendous speed - from 1,100 to 5,200 miles per hour - much faster than the surrounding air. This not only causes a sonic boom from the resulting shock wave but also produces frictional heat high enough to raise the meteoroid's surface to its boiling point. The surface material then simply melts away, or vaporizes, resulting in a fine dust. Most meteors are very small and are vaporized completely in this way. Millions of these burned-out particles fall to Earth as dust everyday.
The outer surfaces of even large meteors melt rapidly. As passing airstreams sweep away the melted upper layer, a new layer is exposed and is melted in turn. The melting surface gives off glowing particles that stream behind the meteor as it speeds through the atmosphere, creating a blazing trail.
Exceptionally bright meteors are called fireballs. Their brightness is thought to be due largely to air in front of meteor that becomes compressed and luminous; the compressed air forms a bright gaseous envelope that is much greater in diameter than the solid meteor itself.
The meteor's flight through the Earth's atmosphere lasts only a few seconds. If the body is large, the heat at its surface does not have time to penetrate deeply into the interior. As the meteor approaches the Earth's surface, air resistance slows it. In the dense lower atmosphere, the body often bursts into fragments to produce a meteorite shower. The greatest meteorite shower in modern history took place over North America on November 12, 1833. If a meteor remains intact, however, the fireball dies and the melted surface solidifies into a dark crust before the meteor has a chance to hit the ground.
Most meteorites break into small particles when they strike the Earth, but on rare occasions they do not. One example, the largest known meteorite, is the Hobl West, which weighs about 60 tons. It was discovered many centuries after it had fallen to Earth in Nambia. The second largest meteorite is the Ahnighito, which weighs about 34 tons. It was discovered in Greenland.
Great Balls of Fire
Comets, Meteorites, Etc.
The asteroids, also called the minor planets, are smaller than any of the nine major planets in the solar system and are not satellites of any major planet. The term asteroid means "starlike" because asteroids appear to be points of light when seen through a telescope.
Most asteroids are located between mars and Jupiter, between 2.1 and 3.3 AUs from the sun. Ceres, the first to be discovered, and the largest, was found by Giuseppe Piazzi on January 1, 1801, and has a diameter of 582 miles. A second asteroid, Pallas, was discovered in 1802. Since then, over 18 thousand asteroids have been identified and astronomers have established orbits for about five thousand of them. Some of these have diameters of only 0.62 miles. Originally, astronomers thought the asteroids were remnants of a planet that had been destroyed; now they believe asteroids to be material that never became a planet, possibly because it was affected by Jupiter's strong gravity.
An asteroid came close to hitting the Earth sometime in 1989. How much damage might it have done?
Asteroid 1989 FC passed within 434,0000 miles of the Earth on March 22, 1989. The impact, had it hit the Earth, would have delivered the energy equivalent of more than 1 million tons of exploding TNT and created a crater up to 4.3 miles across.
What was the Tunguska Event?
On June 30, 1908, a violent explosion occurred in the atmosphere over the Podkamennaya Tunguska river, in a remote part of central Siberia. The blast's consequences were similar to an H-bomb going off, leveling thousands of square miles of forest. The shock of the explosion was heard over 6000 miles away. A number of theories have been proposed to account for this event.
Some people thought that a large meteorite or a piece of anti-matter had fallen to Earth. But a meteorite, composed of rock and metal, would have created a crater and none was found at the impact site. There are no high radiation levels in the area which would have resulted from the collision of anti-matter and matter. Two other theories include a mini-black hole striking the Earth and the crash of an extraterrestrial space ship. However, a mini-black hole would have passed through the Earth and there is no record of a corresponding explosion in the other side of the world.
