The speed of a meteorite body that falls to the Earth, flying from the deepest depths of space, exceeds the second cosmic velocity, whose rate is eleven integers and two tenths of a kilometer per second. This meteorite speedis equal to that which needs to be given to the spacecraft in order to break out of the gravitational field, that is, this speed is acquired by the body due to the attraction of the planet. However, this is not the limit. Our planet is moving in orbit at a speed of thirty kilometers per second. When a moving object of the solar system crosses it, it can have a speed of up to forty-two kilometers per second, and if a celestial wanderer moves along an oncoming path, that is, head to head, then he can collide with the Earth at a speed of up to seventy-two kilometers per second . When a meteorite body enters the upper atmosphere, it interacts with rarefied air, which does not interfere much with the flight, almost without creating resistance. At this point, the distance between the gas molecules is larger than the size of the meteorite itself and they do not interfere with the flight speed, even if the body is quite massive. In the same case, if the mass of the flying body is at least slightly greater than the mass of the molecule, then it slows down already in the uppermost layers of the atmosphere and begins to settle under the action of gravity. That is how about a hundred tons of cosmic matter settles on the Earth in the form of dust, and only one percent of large bodies nevertheless reach the surface.

So, at a height of one hundred kilometers, a freely flying object begins to slow down under the action of friction that occurs in the dense layers of the atmosphere. A flying object encounters strong air resistance. The Mach number (M) characterizes the motion of a solid in a gaseous medium and is measured by the ratio of the speed of the body to the speed of sound in the gas. This number M for a meteorite is constantly changing with height, but most often does not exceed fifty. A rapidly flying body forms an air cushion in front of itself, and compressed air leads to the appearance of a shock wave. The compressed and heated gas in the atmosphere heats up to a very high temperature and the surface of the meteorite begins to boil and spray, taking away the molten and remaining solid material, that is, the ablation process takes place. These particles shine brightly, and the phenomenon of a car, leaving a bright mark. The compression region that arises in front of a meteorite rushing at great speed diverges to the sides and a head wave is formed, similar to that which comes from the ship's running occasion. The resulting cone-shaped space forms a wave of turbulence and rarefaction. All this leads to a loss of energy and causes increased inhibition of the body in the lower layers of the atmosphere.

It may happen that the speed a is from eleven to twenty-two kilometers per second, its mass is not large, and it is mechanically strong enough, then it can slow down in the atmosphere. This contributes to the fact that such a body is not subject to ablation, it can almost invariably fly to the surface of the Earth.

With a further decrease in air more and more slows down meteorite speedand at a height of ten - twenty kilometers from the surface, he completely loses cosmic speed. The body, as it were, hangs in the air, and this part of the long journey is called the delay region. The object gradually begins to cool and ceases to glow. Then, all that remains of a difficult flight falls vertically to the surface of the Earth under the force of attraction at a speed of fifty to one hundred and fifty meters per second. In this case, gravity is compared with air resistance, and the heavenly messenger falls like an ordinary thrown stone. It is this meteorite velocity that characterizes all objects that have fallen to the Earth. In the place of the fall, as a rule, depressions of different sizes and shapes are formed, which depends on the weight of the meteorite and the speed with which it approached the soil surface. Therefore, studying the place of the fall, we can say for sure what was the approximate meteorite speedat the time of collision with the Earth. A monstrous aerodynamic load gives the celestial bodies that came to us, characteristic features by which they can be easily distinguished from ordinary stones. They form a melting crust, the shape is most often cone-shaped or fused-clastic, and the surface as a result of high-temperature atmospheric erosion receives a unique remhalipt relief.

In a previous post, an assessment of the danger of an asteroid threat from space was given. And here we consider what will happen if (when) a meteorite of one size or another all the same falls to Earth.

The scenario and consequences of such an event as the fall of a cosmic body to Earth, of course, depends on many factors. We list the main ones:

Space body size

This factor is naturally a priority. Armageddon on our planet can make a meteorite with a size of 20 kilometers, so in this post we will consider scenarios of falling cosmic bodies from a speck of dust to 15-20 km on the planet. More - it makes no sense, since in this case the scenario will be simple and obvious.

Composition

Small bodies of the solar system can have different composition and density. Therefore, there is a difference whether a stone or iron meteorite will fall on the Earth, or if the comet’s core is loose, consisting of ice and snow. Accordingly, in order to cause the same damage, the comet's nucleus should be two to three times larger than an asteroid fragment (at the same rate of fall).

For reference: more than 90 percent of all meteorites are stone.

Speed

Also a very important factor in the collision of bodies. After all, there is a transition of kinetic energy of motion into heat. And the speed of entry of cosmic bodies into the atmosphere can vary significantly (from about 12 km / s to 73 km / s, for comets - even more).

The slowest meteorites are those catching up with the Earth or catching up with it. Accordingly, those flying towards us will add up their speed with the orbital speed of the Earth, will pass through the atmosphere much faster, and the explosion from their impact on the surface will be several times more powerful.

Where will fall

At sea or on land. It is difficult to say in which case there will be more destruction, everything will just be different.

A meteorite can fall at a place of storage of a nuclear weapon or at a nuclear power plant, then environmental damage can be greater from contamination with radioactive substances than from a meteorite impact (if it was relatively small).

Angle of incidence

Does not play a big role. At those huge speeds at which the cosmic body crashes into the planet, it does not matter at what angle it will fall, since in any case, the kinetic energy of the motion will go into the thermal energy and will be released in the form of an explosion. This energy does not depend on the angle of incidence, but only on mass and speed. Therefore, by the way, all the craters (on the Moon, for example) have a circular shape, and there are no craters at all in the form of some trenches drilled at an acute angle.

How do bodies of different diameters behave when they fall to Earth

Up to a few centimeters

They burn out completely in the atmosphere, leaving a bright trace several tens of kilometers long (a well-known phenomenon called meteor) The largest of them reach altitudes of 40-60 km, but most of these "dust particles" burn out at an altitude of more than 80 km.

Mass phenomenon - within just 1 hour, millions (!!) meteors flare up in the atmosphere. But, taking into account the brightness of the flashes and the radius of the observer's view, at night in one hour you can see from a few pieces to dozens of meteors (during meteor showers - more than a hundred). For a day, the mass of dust deposited on the surface of our planet from meteors is calculated in hundreds, and even in thousands of tons.

From centimeters to several meters

Fireballs   - the brightest meteors, the brightness of the flash of which exceeds the brightness of the planet Venus. The flash may be accompanied by noise effects up to the sound of an explosion. After that, a smoky trail remains in the sky.

Shards of cosmic bodies of this size reach the surface of our planet. It happens like this:

At the same time, stone meteoroids, and especially ice ones, are usually crushed into fragments from explosion and heating. Metal can withstand pressure and fall to the surface entirely:

  The Goba iron meteorite about 3 meters in size, which fell "entirely" 80 thousand years ago in the territory of modern Namibia (Africa)

If the rate of entry into the atmosphere was very high (oncoming trajectory), then such meteoroids are much less likely to fly to the surface, since the force of their friction against the atmosphere will be much greater. The number of fragments into which the meteoroid can be split can reach hundreds of thousands, the process of their falling is called meteor Rain.

In a day, several tens of small (about 100 grams) fragments of meteorites can fall to the Earth in the form of cosmic precipitation. Given that most of them fall into the ocean, and in general, they are difficult to distinguish from ordinary stones, they are rarely found.

The number of cosmic bodies entering our atmosphere about one meter in size is several times a year. If you are lucky, and the fall of such a body will be noticed, there is a chance to find decent fragments weighing hundreds of grams, or even kilograms.

17 meters - Chelyabinsk car

Superbolid   - this is what is sometimes called especially powerful explosions of meteoroids, similar to the one that exploded in February 2013 over Chelyabinsk. The initial size, which then entered the atmosphere of the body according to various expert estimates, varies, on average, it is estimated at 17 meters. Mass - about 10,000 tons.

The object entered the Earth’s atmosphere at a very sharp angle (15–20 °) at a speed of about 20 km / s. He exploded after half a minute at an altitude of about 20 km. The power of the explosion was several hundred kilotons of TNT. This is 20 times more powerful than the Hiroshima bomb, but the consequences here were not so fatal because the explosion occurred at a high altitude and the energy dissipated over a large area, to a large extent, far from settlements.

Less than a tenth of the initial mass of the meteoroid flew to Earth, that is, about a ton or less. The fragments scattered over an area more than 100 long and about 20 km wide. Many small fragments were found, several kilograms in weight, the largest piece weighing 650 kg was lifted from the bottom of Lake Chebarkul:

Damage:   nearly 5,000 buildings were damaged (mostly broken glass and frames), about 1,500 people were injured by shattered glass.

A body of this size could well reach the surface without falling apart into fragments. This did not happen because of the too sharp angle of entry, because before exploding, a meteoroid flew in the atmosphere several hundred kilometers. If the Chelyabinsk meteoroid fell vertically, instead of an air shock wave that broke the glass, there would have been a powerful blow to the surface, which entailed a seismic shock, with the formation of a crater with a diameter of 200-300 meters. About the damage and the number of victims, in this case, judge for yourself, everything would depend on the place of the fall.

Concerning repetition rates   of such events, then after the Tunguska meteorite of 1908 - this is the largest celestial body that fell to Earth. That is, in one century one or more of such guests from outer space can be expected.

Tens of meters - small asteroids

Children's toys are over, move on to more serious things.

If you read the previous post, then you know that the small bodies of the solar system up to 30 meters in size are called meteoroids, more than 30 meters - asteroids.

If an asteroid, even the smallest, encounters the Earth, then it definitely will not fall apart in the atmosphere and its speed will not slow down to the rate of free fall, as it happens with meteoroids. All the huge energy of his movement will be released in the form of an explosion - that is, it will turn into thermal energythat will melt the asteroid itself, and mechanical, which will create a crater, scatter around the rock and fragments of the asteroid itself, and also create a seismic wave.

To quantify the magnitude of such a phenomenon, we can consider for example an asteroid crater in Arizona:

This crater was formed 50 thousand years ago from the impact of an iron asteroid with a diameter of 50-60 meters. The force of the explosion was 8,000 Hiroshima, the diameter of the crater was 1.2 km, the depth was 200 meters, and the edges rose 40 meters above the surrounding surface.

Another event of comparable scale is the Tunguska meteorite. The power of the explosion was 3,000 Hiroshim, but there was a fall of a small cometary nucleus with a diameter of tens to hundreds of meters, according to various estimates. The nuclei of comets are often compared with dirty snow cakes, so in this case no crater arose, the comet exploded in the air and evaporated, knocking down a forest in an area of \u200b\u200b2 thousand square kilometers. If the same comet exploded over the center of modern Moscow, it would destroy all houses right up to the ring road.

Fall frequency   asteroids tens of meters in size - once every several centuries, hundred-meter - once every several thousand years.

300 meters - Apophis asteroid (the most dangerous of the known at the moment)

Although according to the latest NASA data, the probability of the Apophis asteroid falling into the Earth when it flies near our planet in 2029, and then in 2036 is practically zero, nevertheless we will consider the scenario of the consequences of its possible fall, since there are many as yet undiscovered asteroids, and a similar event can still occur, not this time, but another time.

So .. the asteroid Apophis, contrary to all forecasts, falls to Earth ..

The power of the explosion is 15,000 Hiroshima atomic bombs. When hit the mainland, an impact crater with a diameter of 4-5 km and a depth of 400-500 meters occurs, the shock wave demolishes all brick buildings in a zone with a radius of 50 km, less durable structures, as well as trees lying at a distance of 100-150 kilometers from the place fall. A pillar of dust like a mushroom from a nuclear explosion several kilometers high rises into the sky, then the dust begins to spread in different directions, and within a few days spreads evenly throughout the planet.

But, in spite of the greatly exaggerated horror stories that the media usually scare people, a nuclear winter and the end of the world will not come - the Apophis caliber is not enough for this. According to the experience of powerful volcanic eruptions in a not very long history, during which huge emissions of dust and ash also take place in the atmosphere, with such a power of the explosion, the “nuclear winter” effect will be small - the average temperature on the planet will drop by 1-2 degrees, after Six months to a year, everything returns to its place.

That is, this is a disaster not of a global but of a regional scale - if Apophis gets into a small country, he will completely destroy it.

When Apophis enters the ocean, coastal areas will suffer from the tsunami. The height of the tsunami will depend on the distance to the place of impact - the initial wave will have a height of about 500 meters, but if Apophis falls into the center of the ocean, then 10-20 meter waves will reach the coast, which is also a lot, and the storm with such mega the waves will be several hours. If a blow to the ocean occurs near the coast, then surfers in coastal (and not only) cities will be able to ride this wave: (sorry for the black humor)

Recurrence rate   events of a similar scale in the history of the Earth are measured in tens of thousands of years.

We turn to global disasters ..

1 kilometer

The scenario is the same as during the fall of Apophis, only the scale of the consequences is several times more serious and already reaches the global catastrophe of a low threshold (the consequences are felt by all of humanity, but there is no threat of the death of civilization):

Explosion power in "Hiroshima": 50,000, the size of the crater formed when falling to land: 15-20 km. The radius of the destruction zone from the blast and seismic wave: up to 1000 km.

When falling into the ocean, again, it all depends on the distance to the coast, since the waves that appear will be very high (1-2 km), but not long, and such waves will decay quite quickly. But in any case, the area of \u200b\u200bflooded territories will be huge - millions of square kilometers.

Reducing the transparency of the atmosphere in this case from emissions of dust and ash (or water vapor when falling into the ocean) will be noticeable for several years. If it gets into a seismically dangerous zone, the consequences can be aggravated by earthquakes provoked by the explosion.

However, an asteroid of this diameter will not be able to tilt the Earth's axis noticeably or affect the period of rotation of our planet.

Despite the dramatic nature of this scenario, for the Earth it is a rather ordinary event, since it has already happened thousands of times during its existence. Average recurrence   - once every 200-300 thousand years.

Asteroid with a diameter of 10 kilometers - a global catastrophe on a planetary scale

• Explosion power in Hiroshima: 50 million
• The size of the crater formed when falling to land: 70-100 km, depth - 5-6 km.
• The depth of cracking of the earth's crust will be tens of kilometers, that is, up to the mantle (the thickness of the crust under the plains is an average of 35 km). The exit of magma to the surface will begin.
• The area of \u200b\u200bthe destruction zone can be several percent of the Earth’s area.
• In an explosion, a cloud of dust and molten rock rises to a height of tens of kilometers, possibly up to hundreds. The volume of discarded materials - several thousand cubic kilometers - is enough for a light “asteroid fall”, but not enough for a “asteroid winter” and the beginning of the ice age.
• Secondary craters and tsunamis from fragments and large pieces of discarded rock.
• A small, but by geological standards, a decent slope of the earth's axis from the impact - up to 1/10 of a degree.
• When entering the ocean - a tsunami with kilometer (!!) waves extending far deeper into the continents.
• In the case of intense eruptions of volcanic gases, acid rain is possible afterwards.

But this is still not quite Armageddon! Even such grandiose catastrophes, our planet has experienced tens or even hundreds of times. On average, this happens alone. once every 100 million years.   If this happened now, the number of victims would be unprecedented, in the worst case it could be measured in billions of people, moreover, it is not known what social shocks this would lead to. However, despite the period of acid rain and several years of some cooling due to a decrease in the transparency of the atmosphere, in 10 years the climate and biosphere would have completely recovered.

Armageddon

For such a significant event in the history of mankind, an asteroid is required in size 15-20 kilometers   in the amount of 1 piece.

The next ice age will come, most of the living organisms will die, but life on the planet will continue, although it will not be the same as before. As usual, the fittest will survive ..

Such events have also happened more than once. From the moment of the appearance of life on it, armageddons have occurred at least several, and perhaps dozens of times. It is believed that the last time this happened 65 million years ( Chiksulubsky meteorite), when dinosaurs and almost all other species of living organisms died, only 5% of the elect remained, including our ancestors.

Full Armagedets

If a cosmic body the size of the state of Texas crashes into our planet, as was the case in the famous film with Bruce Willis, then even bacteria (though, who knows?) Will not survive, life will have to arise and evolve again.

Conclusion

I wanted to write a review post about meteorites, but I got Armageddon's scripts. Therefore, I want to say that all the events described, starting with Apophis (inclusive), are considered as theoretically possible, since in the next hundred years they will definitely not happen. Why so - is described in detail in a previous post.

I also want to add that all the numbers given here regarding the correspondence of the size of the meteorite and the consequences of its fall to Earth are very approximate. The data in different sources differ, plus the initial factors during the fall of an asteroid of the same diameter can vary greatly. For example, everywhere it is written that the size of the Chiksulubsky meteorite is 10 km, but in one, it seemed to me, an authoritative source, I read that a 10-kilometer stone of such troubles could not have done, so my Chiksulubsky meteorite entered the 15-20 kilometer category .

So, if suddenly Apophis still falls in the 29th or 36th year, and the radius of the affected area will be very different from what is written here - write, I’ll fix it

Cosmos is a space filled with energy. The forces of nature make chaotically existing matter group. Objects are formed with a specific shape and structure. Planets, their satellites, have long been formed in the solar system, but this process does not end. A huge amount of substance: dust, gas, ice, stone and metal, fill the space. These objects are classified.

A body no larger than a dozen meters in size is called a meteoroid; a larger body can be considered an asteroid. A meteor is an object burning in the atmosphere, falling to the surface, it becomes a meteorite.

In the solar system, hundreds of thousands of asteroids are discovered. Some reach more than 500 kilometers in diameter. Arrays of large sizes take a spherical shape and begin to be classified by scientists as dwarf planets. The speed of asteroids is limited by the presence in the solar system, they revolve around the sun. Pallas - is currently considered the largest asteroid, 582 × 556 × 500 km. It has an average speed of 17 kilometers per second, the speed developed by asteroids does not exceed this value by more than two three times. The name of the asteroids is the date of their discovery (1959 LM, 1997 VG). After studying the calculation of the orbit, the object can get its own name.

Celestial bodies inevitably collide with each other. The moon has preserved the result of millions and millions of years of interaction. On earth, huge craters say that once, global destruction occurred. People always strive for control; all potential threats must have methods and technologies to eliminate them. The obvious option with the use of nuclear weapons is ineffective. Most of the explosion energy is simply dissipated in space. It is extremely important to detect a dangerous lump as early as possible, which does not always work out. The good thing is that the larger the body, the easier it is to detect.

Tons of cosmic dust fly into the atmosphere every day, at night you can watch how small meteoric bodies burn up with the so-called “falling stars”. Each year, meteoroids up to several meters in size fall into the airspace of our planet. A meteorite can enter the atmosphere at a speed of 100,000 km / h. At an altitude of several tens of kilometers, speed drops sharply. In general, information about the speed of meteorites is blurred. Limits from 11 to 72 kilometers per second are given for meteorites of the solar system, vagrants from outside develop an order of magnitude greater speed.

February 15, 2013 in the Chelyabinsk region a meteorite fell. Presumably, its diameter was from 10 to 20 meters. The speed of the meteorite is not precisely determined. The bright glow of the car was observed hundreds of kilometers from the epicenter. The car exploded at high altitude. The video captures the flash point, after 2 minutes. 22 sec shock wave comes.

Meteorites are divided into stone and iron. The composition always includes a mixture of elements with a variety of proportional proportions. The structure may be heterogeneous with intersperses. Metal alloy of iron meteorites of excellent quality, suitable for the manufacture of all kinds of products.

Any celestial body that is larger than cosmic dust but inferior to an asteroid is called a meteoroid. A meteoroid falling into the Earth’s atmosphere is called a meteor, while a meteoroid falling onto the Earth’s surface is called a meteorite.

Speed \u200b\u200bin space

The speed of meteoroid bodies moving in outer space can be different, but in any case, it exceeds the second cosmic speed, equal to 11.2 km / s. This speed allows the body to overcome the gravitational attraction of the planet, but it is inherent only to those meteoric bodies that were born in the solar system. For meteoroids that arrive from the outside, higher speeds are also characteristic.

The minimum speed of a meteoroid at a meeting with the planet Earth is determined by how the directions of motion of both bodies relate. The minimum is comparable with the speed of the Earth in orbit - about 30 km / s. This applies to those meteoroids that move in the same direction as the Earth, as if catching up with it. Most of these meteoric bodies, because meteoroids arose from the same rotating protoplanetary cloud as the Earth, therefore, should move in the same direction.

If the meteoroid is moving toward the Earth, then its speed is added to the orbital and therefore is higher. The speed of bodies from a meteor shower called Perseids, through which the Earth passes every year in August, is 61 km / s, and meteoroids from the Leonid stream, with which the planet meets between November 14 and 21, have a speed of 71 km / s.

The highest velocity is typical for cometary fragments, it exceeds the third cosmic velocity - one that allows the body to leave the limits of the solar system - 16.5 km / s, to which it is necessary to add also the orbital velocity and make corrections for the direction of motion relative to the Earth.

Earth meteoroid

In the upper atmosphere, the air almost does not interfere with the movement of the meteor - it is too rare here, the distance between the gas molecules can exceed the size of the average meteorite. But in denser layers of the atmosphere, the friction force begins to influence the meteor, and its motion slows down. At an altitude of 10-20 km from the earth's surface, the body falls into the delay region, losing space velocity and, as it were, freezing in the air.

Subsequently, the resistance of atmospheric air is balanced by Earth's gravity, and a meteor falls on the surface of the Earth like any other body. In this case, its speed reaches 50-150 km / s, depending on the mass.

Not every meteor reaches the earth's surface, becoming a meteorite, many burn out in the atmosphere. You can distinguish a meteorite from an ordinary stone by a melted surface.

Tip 2: What harm can an asteroid flying close to Earth do?

The probability of a meeting of the Earth with a large asteroid is rather small. Nevertheless, it cannot be completely excluded, a slightly higher probability of an asteroid flying near our planet. Despite the fact that there is no direct collision in this case, the appearance of an asteroid near the Earth still carries a number of threats.

During its existence, the Earth has already encountered asteroids, and each time this led to dire consequences for its inhabitants. More than one and a half hundred craters have been discovered on the surface of the planet, the diameter of some of them reaches 100 km.

The fact that the fall of a large asteroid will lead to catastrophic destruction is well understood by any sane person. It is no coincidence that scientists from leading countries of the world have been tracking the flight paths of the most dangerous space bodies for decades, and are developing options to counter the asteroid threat.

One of the most dangerous for earthlings is the asteroid Apophis (Apophis), according to forecasts, it will approach the Earth in 2029 at a distance of 28 to 37 thousand kilometers. This is 10 times less than the distance to the moon. And although scientists claim that the collision probability is negligible, such a close passage of the asteroid can be serious for the planet.

The size of Apophis is relatively small, its diameter is only 270 meters. But every asteroid is surrounded by a whole cloud of small particles, many of which can harm spacecraft launched into orbit. At speeds reaching several tens of kilometers per second, even a speck of dust can cause serious damage. Apophis will pass there, geostationary satellites, it is to them that its small fragments threaten them the most.

Some of the material of asteroids flying near the Earth can fall on its surface, this also conceals its own. Scientists suggest that it is comets that can transfer microscopic organisms from one planet to another. The probability of this is small, but it cannot be completely ruled out.

Despite the fact that the wreckage of a celestial wanderer that has entered the planet’s atmosphere is heated to high temperature, some organisms may well survive. And this, in turn, is a very big threat to all life on Earth. Microorganisms alien to the earth's flora and fauna can become deadly and with rapid reproduction lead to the death of mankind.

Such scenarios look very unlikely, but in reality they are quite possible. Earth medicine still fails to cope even with the flu, which annually leads to the deaths of hundreds of thousands of people. Now imagine a microorganism that has dozens of times higher mortality, multiplies rapidly and can spread easily. His appearance in a large city will be a real disaster, as it will be very difficult to keep the epidemic that has begun.

  The most well-studied among the small bodies of the solar system are asteroids - small planets. The history of their study dates back almost two centuries. As early as 1766, an empirical law was formulated that determined the average distance of the planet from the Sun, depending on the serial number of this planet. In honor of the astronomers who formulated this law, it was called: "Titius-Bode law." a \u003d 0.3 * 2k + 0.4 where the number k \u003d - * for Mercury, k \u003d 0 for Venus, then k \u003d n - 2 for Earth and Mars, k \u003d n - 1 for Jupiter, Saturn and Uranus (n is the serial number of the planet from the sun).

At first, astronomers, preserving the traditions of the ancients, assigned the names of gods, both Greco-Roman and others, to small planets. By the beginning of the 20th century, the names of almost all gods known to mankind appeared in heaven - Greco-Roman, Slavic, Chinese, Scandinavian and even Mayan gods. The discoveries continued, the gods began to be missed, and then the names of countries, cities, rivers and seas, the names and surnames of real living or living people began to appear in the sky. Inevitably, the question of streamlining the procedure for this astronomical canonization of names became. This question is all the more serious because, unlike the perpetuation of memory on Earth (names of streets, cities, etc.), the name of the asteroid cannot be changed. Since its creation (July 25, 1919), the International Astronomical Union (IAU) has been doing this.

The major semiaxes of the orbits of the main part of the asteroids are in the range from 2.06 to 4.09 a. e., and the average value is 2.77 a. e. The average eccentricity of the orbits of minor planets is 0.14, the average inclination of the asteroid’s orbital plane to the Earth’s orbit is 9.5 degrees. The speed of asteroids around the Sun is about 20 km / s, the period of revolution (asteroid year) is from 3 to 9 years. The period of proper rotation of asteroids (i.e., the length of a day on an asteroid) averages 7 hours.

Not a single asteroid of the main belt, generally speaking, passes near the Earth’s orbit. However, in 1932 the first asteroid was discovered, whose orbit had a perihelion distance less than the radius of the Earth’s orbit. In principle, its orbit allowed the approach of an asteroid to the Earth. This asteroid was soon "lost" and rediscovered in 1973. It received the number 1862 and the name Apollo. In 1936, at a distance of 2 million km from the Earth, the asteroid Adonis flew, and in 1937, the asteroid Hermes flew at a distance of 750 thousand km from the Earth. Hermes has a diameter of almost 1.5 km, and was opened just 3 months before its maximum rapprochement with the Earth. After the flight of Hermes, astronomers began to realize the scientific problem of asteroid danger. To date, about 2,000 asteroids are known, whose orbits allow them to approach the Earth. Such asteroids are called asteroids approaching the Earth.

According to their physical characteristics, asteroids are divided into several groups, inside which objects have similar reflective properties of the surface. Such groups are called taxonomic (taxonometric) classes or types. The table shows 8 main basic taxonomic types: C, S, M, E, R, Q, V, and A. Each class of asteroids corresponds to meteorites that have similar optical properties. Therefore, each taxonometric class can be characterized by analogy with the mineralogical composition of the corresponding meteorites.

The shape and size of these asteroids is determined using radar as they pass near the Earth. Some of them are similar to the asteroids of the main belt, but most of them have a less regular shape. For example, the asteroid Toutatis consists of two, or maybe more, bodies in contact with each other.

Based on regular observations and calculations of the orbits of asteroids, the following conclusion can be drawn: there are no known asteroids, about which we can say that in the next hundred years they will come close to Earth. The closest will be the passage of the asteroid Hator in 2086 at a distance of 883 thousand km.

To date, a number of asteroids have passed at distances significantly less than the above. They were open during their next walkthroughs. Thus, while the main danger is not yet discovered asteroids.