Meteorite

A meteorite is a material body Extra-terrestre of comparatively small size which reaches the surface of the Ground. When they are still in space, these bodies are called “Météoroïde S”. Arbitrarily, the météoroïdes are the Bolide S of less than 50 meters in diameter, beyond this size, one speaks about asteroids .

Impacts of meteorites

Interplanetary the total matter mass swept by the Earth is estimated at 1012 kg/jour; this matter is primarily made up of dust, with a number of corpuscles depending (roughly) on the Logarithme on the reverse on their mass, with a threshold of approximately 10-16 kg, below which there is very little dust.

Thus, the Earth hardly meets more than 2000 to 3000 meteorites of more than one kilogram per day.

When they penetrate in the atmosphere, friction on the particles constituting it involves a violent one heating and an emission of light, which forms a meteor or shooting star :

  • dust of approximately 10-14 kg and less is volitilized, but is not destroyed: the formed mineral products will condense and fall very slowly on terrestrial surface;

  • dust of higher face constitutes the Micrométéorite S , part of their matter will not be volitilized and will fall on the ground like grains of sand;
  • in lower part of a certain size (opposite function of the cohesion of their constitutive matter) the majority of the meteorites disaggregate in blocks throughout their crossing in the atmosphere, which reduces the number of the large impacts on the surface of the Earth: approximately 500 stones of the size of a ball of tennis reach the ground thus each year.

Meteorites more massive, fortunately rare (the written human history reports only two of them) can create important crater S at the time of their impact on the ground, or of the Tsunami S in the event of arrival at sea.

The energy released at the time of these impacts can involve, directly or by catastrophic side effects (e.g.: reactivation of deadened volcanos, fires generalized etc), the dispersion of a quantity considerable of particles in the atmosphere, sufficient to modify brutally and durably the Climate on the whole of the Earth. According to one theory Catastrophiste, the extinction of the dinosaurs, which marks the end of the Crétacé, would be explained (see crater) by the consequences of the impact of a meteorite.

Classification of the meteorites

There is not a proof that some of them can be primary education original interplanetary material. It is rather generally thought that the meteorites are fragments released by impact between larger bodies: the Asteroid S (some even seem, from of not to doubt, result from impacts violent one on the Moon and Mars) or released by gravitational disintegration of comets at the time of their passage close to the Sun. One distinguishes two principal types from meteorites according to their body relative:

  • the Chondrite S which come from relatively small bodies (of diameter lower than a few tens of kilometers) which, too small, could not be different internally since their formation. Their constitutive material was formed there is 4,65 billion years, at the same time as the Solar system. The fragments of these small Astéroïde S remained in their original state and are the parents of meteorites primarily stony, consisted of a mixture of Silicate S and metal (of alloys of Fer and Nickel). These meteorites are made of chondres, of the small millimetre-length spheres which condensed starting from the solar Nébuleuse. Among chondrites one distinguishes from many classes: ordinary chondrites (79% in mass), and carbonaceous chondrites (5%), which contain carbon in the form of amino-acids sometimes.

  • “meteorites differentiated”, those which come from bodies parents much larger (of diameters of several hundred kilometers) which were different, i.e. whose bodies parents had an activity Tectonique, like our Ground. Under the effect of a warming causes by the disintegration of unstable elements, these small planets melted and the matter which constitutes them is reorganized: the heaviest elements went to constitute metal cores (as on Earth NiFe) whereas the lightest elements formed a coat and a rock crust. This class of meteorites contains the Achondrite S (8%) (having for origin the crust of the bodies parents), Irons (5%) (having for origin the cores of the bodies parents), and the Pallasites (2%) made of translucent olivine crystals enchased in a metal matrix. These last are most visual.

*Les “Irons” (in the past called “Siderites”) are meteorites mainly made up of a nickel and iron alloy. With a density close to 8, they are the densest meteorites.
*Les “Achondrite S”, brings information to us on the formation and the evolution of the large asteroids and the Planet S. the fragments torn off to the the Moon or with Mars at the time of impacts on their surface, and which landed then on Earth are achondrites, or planetary meteorites.
  • Finally a third group of meteorites, the “meteorites not grouped”, contains a small number of other meteorites, having particular chemical characteristics relative with the members of the principal groups, belong to additional groups or sub-groups.

Study of the meteorites

The study of the meteorites makes it possible to better know the various mechanisms of the formation of our solar system.

It is in particular interesting to note that the various minerals present in a chondrite (resulting from a body relative not differentiated) are identical to those which one can find on a planet (differentiated body) like the ground. Indeed, if one crushes a chondrite fragment until reducing it out of powder, then if one approaches a magnet in order to separate the magnetic particles from those which are not it, one obtains on the one hand the particles of iron/nickel constituting the core of a planet like the Earth and on the other hand mainly of silicates identical to those present in the coat and the earth's crust. This small experiment led the scientists to appronfondir the subject and in particular with better explaining the phenomenon of differentiation of which it was question higher.

Another interesting example relates to part of chondrites known as carbonaceous, which are suspected of coming not from asteroids but from cores of comets. These meteorites contain amino-acids which are the elementary “bricks” of the life and seem to confirm (if their origin is well proven) that the Earth regularly met comets on its way, which could be with the origin of life on our planet.

A last example to finish, with the extremely rare meteorites Martian and lunar. The first make it possible to the scientists to start with better knowing Martian geology before even as samples were not brought back since this planet, which is possible thanks to terrestrial research programs such as ANSMET. The knowledge acquired thanks to these very rare meteorites will be able to help these same scientists in their research when they finally have samples taken on red planet at the time of the missions planned for the years to come. As for the lunar meteorites of origins, they give the opportunity to the scientists not having at their disposal of the samples brought back by the Apollo missions of working on the history of the formation of our satellite. An assumption selected more and more seriously would be that the Moon would come from the collision between the Earth and a star of the size of Mars, which would have torn off and projected out of the terrestrial ground the fruits of this meeting. The phenomenal energy released at the time of the impact would have made it possible ejecta to leave the Earth, remaining however orbits about it around this one and réaccrétant themselves to form the Moon. It would be then about largest the meteorite having ever crossed the Earth, giving rise to our satellite.

History of the meteorites

Probably coming for the majority from the belt from asteroids between Mars and Jupiter, the meteorites are a single source of information on our solar system, its birth, its evolution, its age. In a few decades, the increasingly fine analyzes made in laboratory, space explorations and the astronomical observations upset our knowledge of the solar system. All the meteorites known today on Earth come from the solar system. The Meteoritical Society publishes each year a catalog of new the meteorites analyzed: the Meteoritical Bulletin . There is approximately: 40000 meteorites classified by the Meteoritical Society (at the beginning of 2007). This number increases approximately: 1500 each year.

One distinguishes finally the meteorites which one saw falling and which one found shortly after their landing: they are called “falls observed” or more simply of the “Falls”, in opposition to those which one discovered by chance and which one calls of the “Lucky finds”. The Meteoritical Society allots a name or a number to each meteorite. It is in general about a geographical name of a place close to the place of the discovery.

In France, on November 7th 1492 fell in Alsace to Ensisheim a Chondrite 127 kg: the Meteorite of Ensisheim, one of the most famous falls of the world. It today is preserved at the Palais of Regency with Ensisheim and is kept by the brotherhood St Georges of the Guards of the Meteorite of Ensisheim, which joins together each year, in June, impassioned these celestial stones at the time of a remarkable exchange market. The collectors and hunters of meteorites of the whole world are found there.

Among the remarkable meteorites fallen in France, one must quote Orgueil a meteorite carbonaceous classified Ci, Ornans another carbonaceous which gave its name to a class of meteorites CO, the Eagle , fallen in 1806 in Normandy which was the subject of a scientific report/ratio of Jean-Baptiste Biot of the Academy of Science. More than 2000 individuals (small meteorites) were found in the surroundings of the village of the Eagle.

The larger impact French was identified in 1967 between the towns of Rochechouart in High Vienna, and Chassenon in Charente. The crater approximately 21 km in diameter is not identifiable any more but the rocks fractured by the energy of the impact remain by place. There does not remain any more trace of the meteorite which completely disintegrated under the violence of the shock. This impact took place approximately 214 million years ago.

See too

Related articles

Other definitions

Astroblèmes

  • Meteorite of Chicxulub, peninsula of Yucatan, Mexico, Ø 170 km, 64,98 ± 0,05 My
  • Astroblème de Rochechouart-Chassenon, Charente, France, Ø 23 km, 214 ± 8 My
  • Astroblème de Ries, Bavaria, Germany, Ø 24 km, 15 My

External bonds

  • Hunter of meteorites
  • Meteor-Center, by Pierre-Marie Peeled, hunter of French meteorites
  • World Wide Meteorites, a site of information, analysis, sale and exchange of meteorites
  • French Forum of impassioned meteorites, shattercones, impactites and astroblèmes
  • Meteorite.fr
  • Meteorites of the Sahara
  • the most complete database in the world on the meteorites. Free registration
  • Article on the meteorites
  • Earth Impact Database database of the terrestrial impacts (astroblèmes)
  • Meteoritica - Meteorites & books

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