Asteroid Belt

In the entire solar system there are hundreds of thousands of irregular rocks from small pieces to ones the size of mountains and these mainly move around on the ecliptic plane between the planets Mars and Jupiter. The biggest of these so-called asteroids, of which there are several thousand listed, is Ceres, which has a diameter of nearly 1000 km. More than 90% of a typical asteroid is made up of silicate and about 6% out of iron or nickel, the rest is made up of a mixture of these three and other elements. These small celestial bodies probably originated from a collection of matter between Mars and Jupiter, where no individual planet could form because the interaction with the gravitational field of the gas giant Jupiter prevented it. The orbit distribution of the asteroids also shows radial gaps and clusters, which originated through resonance with Jupiter's path. Depending on their size, speed and material structure, asteroids colliding with the earth produce very bright shooting stars (bolides), which burn up in the atmosphere, or meteorites which reach the earth's surface. As a rule, only big parts of rock are able to get through to the ground. Additionally there are tons of tiny parts, mostly in the form of microscopic dust, which penetrate the earth's atmosphere daily; but these, at least the larger ones, burn up completely and produce meteors (=shooting stars). There is, however, evidence of asteroids colliding with the earth's surface. At the moment we know of about 150 craters which probably originated from asteroids. The impact of an asteroid, 10 - 20 km wide, which formed the Chicxulub crater with a diameter of 170 km on the Mexican peninsula about 65 million years ago, probably led to the extinction of the dinosaurs. Statistically, such a big impact only happens about every 100 million years. About 49.000 years ago the Barringer-meteor-crater in Arizona /USA, with a diameter of ca. 1 km, was formed. In the last century there was an impact which statistically can occur four times every thousand years. On June 30th, 1908 a meteorite of stone collided above the area of Tunguska, Siberia. The celestial body, which was roughly about 100 metres in size, had exploded in the air about 6 - 8 km high; within a radius of 30 km it destroyed the surrounding area , which fortunately was completely uninhabited, and overturned all the trees and partly burned them to the ground. Far more than 1000 asteroids which approach the earth within less than one astronomical unit (AU = distance from earth to sun), have been catalogued up till now. 271 belong to the so-called cruisers of the earth's orbit and therefore to possibly dangerous asteroids (PHAs), from which admittedly there is no danger within the next 20 years. Due to disturbances from the planets, the paths of the asteroids are partly chaotic and that's why a longer prognosis is not easily possible. An atomic explosion in outer space to avert the threatening danger of an asteroid attack has already been considered.

The latest findings were gained by the space probes Galileo and NEAR, which landed on the micro-planet Eros. The next planned missions are the Japanese probe Muses-C (in 2002), which is supposed to bring samples from the asteroid Nereus back to earth, and the ESA/NASA Rosetta-mission.

Meteorites have always been religiously worshipped. A silver- plated meteorite, the "black stone" placed in the corner of the Kaaba of Mecca, is the greatest and holiest shrine of Islam which every practising Muslim should visit on a pilgrimage, the so-called Hadj, once in his life-time. The distribution of the asteroids orbits shows the so-called golden section, which has been known about since ancient times. Things in the golden section seem perfect and well-formed to our eyes. The golden section can be found, among other things, in plants, minerals and planets as well as in music and architecture. A phenomenon similar to the asteroid belt are the countless dust particles which fill the space of the central plane of the planet system inside the earth's orbit. The zodiacal light is created by the scattering and reflection of light against the background of the sun on these fine dust particles. If the sky is not "polluted"  by man-made stray light, the zodiac light can be seen in smog-free air and on a moonless, clear night with the naked eye. Before dawn or after dusk a faint, shimmery vail appears where the ecliptic meets the horizon. Near the equator, in particular, the zodiac light shows itself in clear weather along the configurations of the eclipse as a sloping pyramid of light. There are speculations that the zodiacal light may also have played a part in the "Star of Bethlehem", whose astronomical background, according to our present understanding, was a triple conjunction of the planets Jupiter and Saturn.

 

Der Barringer-Krater in Arizona/USA
Picture: The Barringer-crater in Arizone, USA