The main feature of meteorites is the so-called melting crust. It has a thickness of no more than 1 mm and covers the meteorite on all sides in the form of a thin shell. The black bark on stony meteorites is especially noticeable.

The second sign of meteorites is the characteristic pits on their surface. Meteorites usually come in the form of debris. But sometimes there are meteorites with a remarkable cone shape. They resemble a projectile head. This cone-shaped shape is formed as a result of the “sharpening” action of air.

The largest single meteorite was found in Africa in 1920. This meteorite is iron and weighs about 60 tons. Usually meteorites weigh several kilograms. Meteorites weighing tens, and even more so hundreds of kilograms fall very rarely. The smallest meteorites weigh fractions of a gram. For example, at the site of the fall of the Sikhote-Alin meteorite, the smallest specimen was found in the form of a grain weighing only 0.18 G; The diameter of this meteorite is only 4 mm.

Stone meteorites fall most often: on average, out of 16 meteorites that fall, only one turns out to be iron.

WHAT ARE METEORITES MADE OF?

Studying chemical composition meteorites, scientists have found that meteorites consist of the same chemical elements that are found on Earth. No new elements were found in them.

The eight chemical elements most commonly found in meteorites are iron, nickel, sulfur, magnesium, silicon, aluminum, calcium and oxygen. All other chemical elements of the periodic table are found in meteorites in negligible, microscopic quantities. By combining chemically with each other, these elements form various minerals. Most of these minerals are found in terrestrial rocks. And in very insignificant quantities minerals were found in meteorites that do not and cannot exist on Earth, since it has an atmosphere with a high oxygen content. When they combine with oxygen, these minerals form other substances.

Iron meteorites are composed almost entirely of iron combined with nickel, while stony meteorites are composed primarily of minerals called silicates. They consist of compounds of magnesium, aluminum, calcium, silicon and oxygen.

The internal structure of iron meteorites is especially interesting. Their polished surfaces become shiny like a mirror. If you etch such a surface with a weak acid solution, an intricate pattern usually appears on it, consisting of individual stripes and narrow edges intertwining with each other. On the surfaces of some meteorites, parallel thin lines appear after etching. All this is the result of the internal crystalline structure of iron meteorites.

The structure of stone meteorites is no less interesting. If you look at a fracture in a stone meteorite, you can often see even with the naked eye small round balls scattered across the surface of the fracture. These balls sometimes reach the size of a pea. In addition to them, scattered tiny shiny particles are visible in the fracture white. These are inclusions of nickel iron. Among such particles there are golden sparkles - inclusions of a mineral consisting of iron combined with sulfur. There are meteorites that look like an iron sponge, in the voids of which grains of the yellowish-green color of the mineral olivine are contained.

ORIGIN OF METEORITES

Most scientists believe that meteorites are fragments of one or (more likely) several large celestial bodies, similar to asteroids that previously existed in the solar system.

Soviet scientists - Academician V. G. Fesenkov, S. V. Orlov and others - believe that asteroids and meteorites are closely related to each other. Asteroids are giant meteorites, and meteorites are very small, dwarf asteroids. Both are fragments of planets that billions of years ago moved around the Sun between the orbits of Mars and Jupiter. These planets apparently fell apart as a result of the collision. Countless fragments of various sizes were formed, down to the smallest grains. These fragments are now carried in interplanetary space and, colliding with the Earth, fall onto it in the form of meteorites.

HELP OF THE POPULATION IN COLLECTING METEORITES

Meteorites always fall unexpectedly, and it is impossible to predict when and where this will happen. Therefore, specialists cannot prepare in advance for observations of meteorite falls. Meanwhile, the study of the movements of meteoric bodies in the earth's atmosphere is of very great scientific importance.

In addition, by observing the fireball, you can approximately determine the place where the meteorite could have fallen and search for it there. Therefore, the public can greatly help scientists in their work if eyewitnesses of the meteorite fall describe in detail all the phenomena that they noticed during the movement of the fireball and the fall of the meteorite to the Earth.

Upon receipt large number such descriptions made by eyewitnesses in different populated areas, it is possible to quite accurately determine the path of a meteoroid in the earth's atmosphere, the height of the appearance and disappearance of the fireball, as well as the inclination and direction of its path. Reports of meteorites should be sent to the Committee on Meteorites of the USSR Academy of Sciences.

If a meteorite is found, under no circumstances should it be crushed. It is necessary to take all measures to protect it and transfer it to the Committee on Meteorites.

When describing the fireball phenomenon, it is necessary, if possible, to answer the following questions: 1) date and time of the fall; 2) observation location; 3) direction of movement of the car; 4) duration of the car’s flight in seconds; 5) the size of the fireball compared to the apparent size of the Moon or Sun; 6) car color; 7) whether the area was illuminated during the flight of the car; 8) whether fragmentation of the car was observed; 9) whether there was a trace left behind the car; what is its form and subsequent change, as well as the duration of visibility; 10) what sounds were observed during the flight of the car and after its disappearance.

The description must also indicate the last name, first name, patronymic and address of the observer.

In most cases, cosmic bodies that give rise to meteorites are completely slowed down in the atmosphere, reaching altitudes of 20-10 km. In this case, a thin molten layer solidifies, forming a dark relief shell - a melting crust. If you examine this cortex under a microscope, you can discover its complex structure, which is the result of interaction cosmic bodies with atmosphere. As a rule, frozen smudges, streams, and splashed drops are visible. Due to the low landing speed of meteorites, these traces of atmospheric processing are well preserved.

You just need to remember that these are traces left from processing in the immediate vicinity of the area of ​​complete braking, where the conditions of interaction of the body with the air are different from the conditions at high altitudes. At low altitudes, where the density of the atmosphere is high, a cushion of compressed air forms in front of the body, which heats up to several thousand and tens of thousands of kelvins. Therefore, it is incorrect to assume that the structure of the melting crust during the entire atmospheric flight has the same form as before the region of complete deceleration. Moreover, it is impossible, based on the structure of the melting crust of meteorites, to conclude that the melting and blowing away of molten drops is the only mechanism for the destruction of smaller meteoroid bodies.

Based on their chemical composition, meteorites are divided into three types: iron, stony, and stony-iron. Iron is the main component of type 1 meteorites. If you polish the surface of such a meteorite and then etch it with a solution of some acid, their amazing crystalline structure will clearly appear in the form of a complex “abstract” pattern - a set of intersecting stripes. Perhaps iron meteorites are fragments of the inner central part of celestial bodies (large asteroids) that disintegrated under the influence of some reason.

Stony meteorites are divided into two main groups: chondrites and achondrites, depending on whether they contain round glassy inclusions called chondrules. Apart from meteorites, chondrules are not found anywhere else. Chondrites are the most common type of stony meteorite and have a very uniform chemical composition. Achondrites are much less common. Some of their properties resemble those of chondrules in chondrites.

Much rarer are iron-stone meteorites - mesosiderites. They resemble a metallic porous sponge filled with a transparent yellow-green mineral - olivine. They contain up to 45% nickel iron.

A detailed study of the chemical composition of meteorites is of interest for many reasons. In particular, from it one can obtain certain information about the relative content of chemical elements in solar system, as well as restore the picture of the origin of meteorites. As a result of laboratory research, almost the entire periodic table was found in them. The most common elements in meteorites are iron, calcium, aluminum, oxygen, silicon, magnesium, nickel, and sulfur. Valuable metals have also been found in meteorites. However, trying to get rich from meteorite mining is a completely hopeless endeavor: to extract 1 g of gold, you need to grind a whole ton of meteorite matter!

Of course, one should not think that all meteorites contain different elements in the same quantities or in the same proportions. Thus, the nickel content, which is always higher in meteorites than in terrestrial rocks, can vary greatly. In some specimens the nickel content reaches 30-40%, while in others it drops to 5%.

Now that a whole “library” of information about the composition of various meteorites has been accumulated, there are sufficient grounds for solving the problem of the patterns of the relationship various elements in meteorite samples. Thus, it has already been established that an increase in the nickel content in a meteorite is necessarily accompanied by a decrease in the content or even absence of some other elements. Of course, this close connection between the contents of some elements and others may be the key to solving many problems associated with the formation of meteorite matter.

Of undoubted interest is the study of the isotopic composition of the chemical elements that make up meteorites. It turned out to be, in most cases, identical to the isotopic composition of the same elements of terrestrial and lunar origin.

Natural radioactive elements provide irreplaceable assistance in studying questions about the origin of chemical elements. The presence of radioactive chemical elements in meteorites provides very important information about their age, which is determined by using the laws of decay of natural radioactive isotopes. For example, some isotopes of thorium and uranium, which have long half-lives (from 700 million to 14 billion years), decay to form different isotopes of lead. At any given time, almost all decaying matter will consist of isotopes of thorium, uranium and lead. Gradually the amount of lead will increase.

In order to determine how much time has passed since the final formation of meteorite matter, it is necessary to find the relative concentrations of uranium, thorium and lead isotopes. Once the substance has solidified (if it has melted), further chemical separation of the elements that make up the meteorite becomes impossible (i.e., the radioactive elements uranium and thorium and their decay product, lead, become bound). A study of the modern lead isotopic composition and the relative abundances of uranium and thorium in many stony meteorites gives an age of the meteorite material of approximately 4.6 billion years.

While traversing the expanses of interplanetary space before falling to Earth, meteorites are constantly exposed to cosmic rays. Possessing enormous kinetic energies, cosmic rays, acting on these bodies, form stable and unstable cosmogenic isotopes in them. The content of these isotopes determines the time of independent existence of the meteorite substance (counted, say, from the moment it breaks off from the asteroid). It ranges from tens of thousands to hundreds of millions of years.

Cosmogenic isotopes also play an exceptional role in determining the time intervals since the fall, i.e., the terrestrial ages of meteorites. It was thanks to measurements of cosmogenic isotopes that it was shown that these ages can reach tens and hundreds of thousands of years. The content of cosmogenic isotopes also makes it possible to determine the size and mass of meteorites before they fall to Earth. This takes advantage of the fact that the concentration of isotopes decreases noticeably with depth.

Most often, when exposed to cosmic rays, one of the helium isotopes is formed in meteorites. Samples taken from various parts meteorite, are introduced into an atomic reactor, where, when irradiated with a stream of slow neutrons, the helium isotope is converted into the hydrogen isotope - tritium. Since tritium is radioactive, its content can be easily determined using meters. Based on the change in tritium content (and, consequently, helium isotopes) with depth in a meteorite, the average intensity of cosmic rays bombarding the sample is estimated. Then contours of the same helium isotope content are constructed, from which the original shape of the meteorite is determined. For example, if the meteorite had the shape of a ball, then the contours will look like concentric circles. Based on the content of the helium isotope, the “pre-atmospheric” dimensions of the body, its volume and mass are estimated.

If the chemical composition of meteorites practically does not differ from terrestrial rocks, then the same cannot be said about the mineral composition. Rarely found or completely unknown minerals on Earth were discovered in meteorites, some of which were named after scientists who studied meteorites (for example, krinovite - after the name of the famous Soviet researcher E. L. Krinov). Some rare types of meteorites contain tiny grains of diamond, apparently resulting from some kind of impact.

A meteorite is a body of cosmic origin that fell on the surface of a large celestial object. Most meteorites found have a mass of several grams to several kilograms (the largest meteorite found is Goba, which was estimated to weigh about 60 tons). It is believed that 5-6 tons of meteorites fall to the Earth per day, or 2 thousand tons per year.

A cosmic body up to several meters in size, flying in orbit and entering the Earth's atmosphere, is called a meteoroid, or meteoroid. Larger bodies are called asteroids. Phenomena generated when meteoroids pass through the Earth's atmosphere are called meteors or, in general, meteor showers; especially bright meteors are called fireballs. Solid of cosmic origin that fell on the surface of the Earth is called a meteorite. Other names for meteorites: aerolites, siderolites, uranolites, meteorolites, betiliams, sky, air, atmospheric or meteor stones, etc.

A crater (astrobleme) may form at the site where a large meteorite falls. One of the most famous craters in the world is Arizona. It is assumed that the largest meteorite crater on Earth - Wilkes Earth Crater (diameter about 500 km).

External signs of a meteorite

The main external features of a meteorite are a melting crust, regmaglypts and magnetism. In addition, meteorites usually have irregular shape(although round or cone-shaped meteorites are also found).

Melting crust

A fusion crust forms on a meteorite as it moves through earth's atmosphere, as a result of which it can heat up to a temperature of about 1800°. It is a melted and re-hardened thin layer of meteorite material. As a rule, fusion bark has a black color and a matte surface; Inside, the meteorite is lighter in color.

Regmaglypts

Regmaglypts are characteristic depressions on the surface of a meteorite, reminiscent of fingerprints in soft clay. They also occur when a meteorite moves through the earth's atmosphere, as a consequence of ablation processes.

Magnetic properties

Meteorites have magnetic properties, and not only iron, but also stone. This is explained by the fact that most stony meteorites contain inclusions of nickel iron.

Composition of meteorites

Meteorites are divided into three groups based on their composition:

1. Stone
   1. chondrites (carbonaceous chondrites, ordinary chondrites, enstatite chondrites)
2. Iron(or outdated name - siderites)
3. Iron-stone
   1. pallasites
   2. mesosiderites

Stone meteorites

The most common meteorites are stony meteorites (92.8% of falls). They consist mainly of silicates: olivines and pyroxenes.

Chondrites

The vast majority of stony meteorites (92.3% stony, 85.7% total number falls) - chondrites. They are called chondrites because they contain chondrules - spherical or elliptical formations of predominantly silicate composition. Most chondrules are no more than 1 mm in diameter, but some can reach several millimeters. Chondrules are found in a detrital or fine-crystalline matrix, and often the matrix differs from chondrules not so much in composition as in crystal structure. The composition of chondrites almost completely replicates the chemical composition of the Sun, with the exception of light gases such as hydrogen and helium. Therefore, it is believed that chondrites formed directly from the protoplanetary cloud surrounding the Sun, through the condensation of matter and the accretion of dust with intermediate heating.

Achondrites constitute a very heterogeneous class of meteorites. They differ significantly from commonly encountered chondrites, primarily in the absence of chondrules. They are similar in composition and structure to terrestrial basalts. All achondrites, to one degree or another, underwent melting, which destroyed the chondrules. Achondrites are a fairly common type of meteorite. They make up about 8% of all meteorites found. Achondrites make up 7.3% of stony meteorites. These are fragments of protoplanetary and planetary bodies that have undergone melting and differentiation by composition (into metals and silicates). During their evolution, they were exposed to high temperatures, meaning that at some point they dissolved into magma. When magma cools and crystallizes, it creates concentric layered structures. Generally speaking, an achondrite is a stony meteorite that is formed from the molten material of its original source; they resemble basalts formed by magmatic processes in the bowels of the Earth. Thus, achondrites have a differentiated structure, having lost a significant part of their original materials, including metals, and, as a rule, do not contain chondrules.

Iron meteorites

The largest known meteorites are iron ones. Iron meteorites are composed of an iron-nickel alloy. They account for 5.7% of falls. The largest of them all is found at the impact site in Goba, Namibia, weighing 59 tons. Iron meteorites rarely change shape when entering the atmosphere and suffer much less from the effects of ablation when passing through dense layers of air. All iron meteorites ever found on Earth weigh more than 500 tons, and they make up approximately 89.3% of the mass of all known meteorites. Despite these facts, iron meteorites are rare. Iron meteorites are composed primarily of iron and nickel. Most of them contain only minor mineral impurities. There is great variety among iron meteorites and it has always been difficult to classify them. In fact, they are divided into 13 groups according to their chemical composition, Special attention pay attention to the amount of gallium, germanium and iridium contained in meteorites in hundredths of a percent. Most of the known achondrites are of the so-called HED type, and according to many geochemists, they originate from the asteroid Vesta. Other achondrites come from Mars, the Moon, and other as-yet unidentified asteroids.

Iron-silicate meteorites

Iron silicate meteorites have a composition intermediate between stony and iron meteorites. They are relatively rare (1.5% incidence).

Pallasite (from the Pallas iron meteorite) is a class in the type of stony-iron meteorites. This rare type of stony-iron meteorite is an iron-nickel base interspersed with olivine crystals (sometimes up to 15 mm). Named in honor of academician P.S. Pallas, who described it as native iron. The nickel content in the metal is about 10%. Pallasite consists of approximately equal amounts of nickel iron and olivine. The peculiar structure of Pallasite indicates that they were formed in the absence, at least significant, gravitational forces. Pallasites are, without a doubt, the most beautiful meteorites, especially when sawn and polished!

Mesosiderites are stony-iron meteorites consisting of approximately equal parts iron, nickel and silicate minerals (olivine, pyroxenes and calcium feldspars). Mesosiderites have a heterogeneous breccia-like structure. Silicate minerals and metals are often present in them in the form of rounded and acute-angled fragments and fine-grained intergrowths. Composition of Mesosiderites (on average): 45% nickel iron (in the form of inclusions in the rock mass), 30% hypersthene, 16.4% anorthite and small amounts of some other minerals. Mesosiderites are very rare meteorites. As of June 2009, only 145 mesosiderites were known (44 of them in Antarctica). In 7 cases out of 145 discovered mesosiderites, they were observed to fall. Some mesosiderite fragments are among the largest known meteorites (up to several tons).

Meteorite, meteor, meteoroid

Research and numerous analyzes allowing a thorough study chemical composition of meteorites, allowed us to draw surprising conclusions. The stones that flew to Earth from the unexplored depths of the Universe contain exactly the same elements as the rocks that make up our planet. The meteorite contains the following chemical elements: oxygen, hydrogen, carbon, sulfur, nitrogen, chlorine, potassium, sodium, calcium, silicon, cobalt, tin, copper, titanium, arsenic. Also spectral analysis showed the presence of barium, lithium, bismuth and zinc. From all of the above it follows that meteorites contain at least a third of the elements characteristic of our planet. Most likely, further study of these space aliens will show the presence in them of other elements that have not yet been discovered due to the small amount of material being studied. If we calculate the average content of elements common on Earth, it will be identical to the composition of meteorites - ninety-four percent. Chemical composition of meteorites It is also interesting because the ratio of iron - ninety-one percent, nickel - eight point four and cobalt - zero point six in iron meteorites is almost exactly the same with the distribution of these elements on Earth. In this case

For meteorites and terrestrial rocks, a pattern based on the Oddo-Harkins law is suitable: an element with an even serial number is found more often than with an odd serial number.

This once again confirms the theory that substances are all substances in outer space consist of the same elements and they are identical in composition. Even the isotopic composition of each of these elements is similar in meteorites and terrestrial rocks.

Main chemical elements meteorites are iron, nickel, sulfur, magnesium, oxygen, silicon, calcium and aluminum. In some cases chemical composition of meteorites may deviate from the average, sometimes in iron meteorites the nickel content can vary significantly from five to thirty percent. It has also been established that the quantitative ratio of rare impurities can be different, for example, if a meteorite contains more nickel, then it will certainly contain less gallium.

Other elements of the periodic table are found in meteorites in very small quantities. Entering into each other chemical reaction, they form, many of which were only later discovered on Earth, but there are also those that confirm the extraterrestrial origin of meteorites, since the impossibility of their presence on our planet is due to the large amount of oxygen in the air. If they were formed here, the results would be completely different compounds.

Precious and rare earth elements are found in meteorites, but in very small quantities - one gram per ton of meteorite matter.

There are also gases in meteorites, so nitrogen, oxygen, carbon dioxide and carbon monoxide. Moreover, carbon dioxide predominates in stone meteorites, and hydrogen and carbon monoxide predominate in metal meteorites. Some radioactive elements, such as uranium, thorium, helium, and radium, were also discovered in space travelers. The content of such elements is negligible and is twenty times less than what is found in earthly rocks. Availability radioactive elements made it possible by measuring their quantity and the products of their decay to determine the age of celestial bodies, that is, the time when the solidification of the substance from which meteorites are composed occurred.

Many scientists believed that the chemical composition of meteorites should be similar to lunar soil. They assumed that the formation of meteorites occurs by “knocking out” from the fall of another cosmic body.

At first, this hypothesis was accepted, but later calculations showed a low probability that such meteorites could hit the Earth's surface. In addition, the study of lunar rocks brought to Earth by astronauts and automatic stations showed that these rocks differ in their chemical composition from extraterrestrial “aliens.”

Composition of extraterrestrial substances

The chemical composition of meteorites is mainly stone, stone-iron and a small part consists of iron.

The chemical composition of most stony meteorites is chondrites.

Chondrites are molten silicates and contain peculiar spherical particles (chondrules) - ball-shaped crystalline drops dispersed in the main, fine-grained matter.

Chondrules are formed from common, widespread minerals known from terrestrial rocks, such as olivine and pyroxene.

More than a century of research into chondrules shows that they are the remains of molten matter that then crystallized. Chondrules are quite small, some of them are barely visible on a meteorite fragment with the naked eye. They were discovered more than 100 years ago by the prominent English scientist Henry Clifton Sorby. Chondrules can be clearly seen in a section using a petrographic apparatus (microscope).

Other minerals found in stony meteorites are feldspars, also familiar from terrestrial rocks. Feldspars account for half the mass earth's crust and two-thirds of the Earth's volume. Interestingly, pieces of cosmic matter originating from distant planets have a mineralogical structure similar to those on Earth rocks. There are indeed very few minerals in meteorites that geologists have not encountered on Earth.

In general, minerals consist of the basic elements: oxygen, silicon, aluminum, iron, magnesium, calcium, sodium and potassium, which make up 98% of the Earth's weight.

In addition to silicates, which include olivine, pyroxene and feldspar, fragments and grains of metals and pieces of sulfides are also commonly found in chondrite meteorites. They can be classified as an iron-stone type. This is how they differ from terrestrial rocks. The combination of sulfides and silicates is unusual for most terrestrial rocks, and the presence of metal in them is an extremely rare occurrence.

The chemical composition of meteorites proves to be similar to terrestrial rocks and to the most common “terrestrial” elements. Obviously, an analogy can be drawn that other terrestrial planets have gone through a development history similar to the path traversed by the Earth, but are related to the structure of meteorites.

The more detailed the chemical composition of chondrite meteorites is studied, the more obvious their similarity with the structure of the Sun becomes. Of course, hydrogen and helium should be excluded, after which the similarity in the ratio of the main elements and the content of trace elements is revealed. If we do not lose sight of the fact that the Sun is an ordinary star, then we can assume that meteorites are widespread cosmic material consisting of minerals like the Earth.

Some chondrites even contain carbon and water, as well as certain amounts of volatile substances. This proves that since their origin they have not undergone any changes, since during the smelting process, which, for example, igneous rocks undergo, some elements would be separated: volatile from non-volatile, metals from silicates and sulfides, water and carbon would disappear.

Therefore, scientists believe that chondrites are primitive building blocks of the solar system.

It is possible that it is matter similar to meteorites that is the main building material of terrestrial planets and others.

Iron extraterrestrial substances

There are also iron meteorites consisting of iron combined with nickel and cobalt. The number of iron meteorites found is small and amounts to about 6%.
No gold or extremely rare substances were found in extraterrestrial incoming substances. found in objects of unearthly origin.