How fast is an asteroid moving through space? Meteorites that fell to Earth: a gift from the Universe or space destroyers? Meteorites that fell on our planet

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

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

Space body size

This factor, of course, is paramount. Armageddon on our planet can arrange a meteorite 20 kilometers in size, so in this post we will consider scenarios for the fall of cosmic bodies on the planet ranging in size from a grain of dust to 15-20 km. 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 falls to the Earth, or a loose comet nucleus consisting of ice and snow. Accordingly, in order to inflict the same damage, the comet nucleus must be two to three times larger than the asteroid fragment (at the same fall velocity).

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

Speed

Also a very important factor in the collision of bodies. After all, here there is a transition of the kinetic energy of motion into thermal energy. 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 that are catching up with the Earth or being overtaken by it. Accordingly, those flying towards us will add their speed to the orbital speed of the Earth, will pass through the atmosphere much faster, and the explosion from their impact on the surface will be many times more powerful.

Where will it fall

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

A meteorite may fall on a nuclear weapons storage site or on a nuclear power plant, then the harm to the environment may be more from radioactive contamination than from a meteorite impact (if it was relatively small).

Angle of incidence

Doesn't 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 falls, since in any case the kinetic energy of motion will turn into heat and be released in the form of an explosion. This energy does not depend on the angle of incidence, but only on mass and velocity. Therefore, by the way, all craters (on the Moon, for example) have a circular shape, and there are absolutely no craters in the form of some trenches drilled at an acute angle.

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

Up to several centimeters

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

A massive phenomenon - within just 1 hour, millions (!!) of meteors flare up in the atmosphere. But, taking into account the brightness of the flares and the radius of the observer's view, at night in one hour you can see from a few to dozens of meteors (during meteor showers - more than a hundred). During the day, the mass of dust from meteors that has settled on the surface of our planet is estimated in hundreds, and even 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 is left in the sky.

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

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

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

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

Several tens of small (about 100 grams) fragments of meteorites can fall to Earth in the form of cosmic precipitation per day. Given that most of them fall into the ocean, and in general, they are difficult to distinguish from ordinary stones, they are quite rare to find.

The number of entries into our atmosphere of cosmic bodies about a 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 fireball

Superbolide- this is sometimes called especially powerful explosions of meteoroids, like the one that exploded in February 2013 over Chelyabinsk. According to various expert estimates, the initial size of the body that entered the atmosphere then varies, on average it is estimated at 17 meters. Weight - 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/sec. It exploded in 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 here the consequences were not so fatal because the explosion occurred at a high altitude and the energy was scattered over a large area, largely far from settlements.

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

Damage: almost 5,000 buildings were damaged (mostly broken glass and frames), about 1.5 thousand people were injured by glass fragments.

A body of this size could easily reach the surface without falling apart into fragments. This did not happen due to the too acute angle of entry, because before exploding, the meteoroid flew several hundred kilometers in the atmosphere. If the Chelyabinsk meteoroid had fallen vertically, then instead of an air shock wave breaking the glass, there would have been a powerful impact on the surface, resulting in 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 rate of similar events, then after the Tunguska meteorite of 1908, this is the largest celestial body that fell to Earth. That is, one or more such guests from outer space can be expected in one century.

Tens of meters are small asteroids

Children's toys are over, let's 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 one, meets the Earth, then it will definitely not fall apart in the atmosphere and its speed will not slow down to the speed of free fall, as happens with meteoroids. All the huge energy of its movement will be released in the form of an explosion - that is, it will turn into thermal energy, which will melt the asteroid itself, and mechanical, which will create a crater, scatter earth rock and fragments of the asteroid itself around, and also create a seismic wave.

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

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 8000 Hiroshima, the diameter of the crater is 1.2 km, the depth is 200 meters, the edges rise above the surrounding surface by 40 meters.

Another event comparable in scale is the Tunguska meteorite. The power of the explosion was 3000 Hiroshima, but here there was a fall of a small comet nucleus with a diameter of tens to hundreds of meters, according to various estimates. Comet nuclei are often compared to dirty snow cakes, so in this case no crater appeared, the comet exploded in the air and evaporated, knocking down a forest over an area of 2 thousand square kilometers. If the same comet exploded over the center of modern Moscow, it would destroy all the houses up to the ring road.

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

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

Although, according to the latest data from NASA, the probability of the Apophis asteroid hitting the Earth during its passage near our planet in 2029 and then in 2036 is practically zero, we still consider the scenario of the consequences of its possible fall, since there are many asteroids that have not yet been discovered, and such an event can still happen, 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 it hits the mainland, an impact crater appears with a diameter of 4-5 km and a depth of 400-500 meters, the shock wave demolishes all brick buildings in a zone with a radius of 50 km, less durable buildings, as well as trees fall at a distance of 100-150 kilometers from the place fall. A column of dust rises into the sky, similar to a mushroom from a nuclear explosion several kilometers high, then the dust begins to spread in different directions, and spreads evenly over the entire planet for several days.

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

That is, this is not a catastrophe of a global, but 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 quite a lot, and the storm lasts with such mega- waves will be several hours. If the impact into the ocean occurs near the coast, then surfers in coastal (and not only) cities will be able to ride such a wave: (sorry for the dark humor)

Recurrence frequency events of this magnitude in the history of the Earth is measured in tens of thousands of years.

Let's move on to global catastrophes ..

1 kilometer

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

The power of the explosion in "Hiroshima": 50,000, the size of the crater formed when it fell to land: 15-20 km. The radius of the destruction zone from the explosive and seismic waves: up to 1000 km.

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

The decrease in atmospheric transparency in this case from emissions of dust and ash (or water vapor falling into the ocean) will be noticeable for several years. If you enter 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 noticeably tilt the earth's axis or affect the period of rotation of our planet.

Despite not all the drama of this scenario, for the Earth this is a rather ordinary event, since it has already happened thousands of times throughout its existence. Average repetition frequency- once every 200-300 thousand years.

An asteroid with a diameter of 10 kilometers is a global catastrophe on a planetary scale

The power of the explosion in "Hiroshima": 50 million
The size of the crater formed when falling on 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 earth's crust under the plains is on average 35 km). Magma will come to the surface.
The area of the destruction zone can be several percent of the Earth's area.
During the explosion, a cloud of dust and molten rock will rise to a height of tens of kilometers, possibly up to a hundred. The volume of ejected materials - several thousand cubic kilometers - is enough for a light "asteroid autumn", but not enough for an "asteroid winter" and the beginning of an ice age.
Secondary craters and tsunamis from fragments and large pieces of ejected rock.
A small, but by geological standards, a decent tilt of the earth's axis from the impact - up to 1/10 of a degree.
When it hits the ocean - a tsunami with kilometer-long (!!) waves that go far deep into the continents.
In the case of intense eruptions of volcanic gases, acid rain is possible later.

But this is not quite Armageddon yet! Even such grandiose catastrophes our planet has already experienced dozens or even hundreds of times. On average, this happens one once every 100 million years. If this happened at the present time, 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 upheavals this would lead to. However, despite the period of acid rains and several years of some cooling due to a decrease in the transparency of the atmosphere, in 10 years the climate and the biosphere would have completely recovered.

Armageddon

For such a significant event in the history of mankind, an asteroid the size of 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 no longer be the same as before. As always, the fittest will survive.

Such events have also happened more than once since the emergence of life on it, Armageddons have happened at least a few, and maybe dozens of times. It is believed that the last time this happened 65 million years ( Chicxulub meteorite), when dinosaurs and almost all other species of living organisms died, only 5% of the elect remained, including our ancestors.

Full Armageddon

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

Output

I wanted to write a review post about meteorites, but the scenarios of Armageddon turned out. Therefore, I want to say that all the events described, starting with Apophis (inclusive), are considered as theoretically possible, since they will definitely not happen in the next hundred years at least. Why this is so is detailed in the previous post.

I also want to add that all the figures given here regarding the correspondence between 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 in the fall of an asteroid of the same diameter can vary greatly. For example, everywhere it is written that the size of the Chicxulub meteorite is 10 km, but in one, as it seemed to me, authoritative source, I read that a 10-kilometer stone could not do such troubles, so my Chicxulub meteorite entered the 15-20 km 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 will correct

However, in space everything is different, some phenomena are simply inexplicable and defy any laws in principle. For example, a satellite launched a few years ago, or other objects will rotate in their orbit and never fall. Why it happens, how fast does a rocket fly into space? Physicists suggest that there is a centrifugal force that neutralizes the effect of gravity.

Having done a small experiment, we ourselves can understand and feel this without leaving our homes. To do this, you need to take a thread and tie a small load to one end, then unwind the thread around the circumference. We will feel that the higher the speed, the clearer the trajectory of the load, and the more tension on the thread, if the force is weakened, the rotation speed of the object will decrease and the risk that the load will fall increases several times. With such a small experience, we will begin to develop our topic - speed in space.

It becomes clear that high speed allows any object to overcome the force of gravity. As for space objects, each of them has its own speed, it is different. Four main types of such speed are determined, and the smallest of them is the first. It is at this speed that the ship flies into Earth's orbit.

In order to fly out of it, you need a second speed in space. At the third speed, gravity is completely overcome and you can fly out of the solar system. Fourth rocket speed in space will allow you to leave the galaxy itself, this is about 550 km / s. We have always been interested rocket speed in space km/h, when entering orbit, it is 8 km / s, beyond it - 11 km / s, that is, developing its capabilities up to 33,000 km / h. The rocket gradually increases its speed, full acceleration begins from a height of 35 km. Speedspacewalk is 40,000 km/h.

Speed in space: record

Maximum speed in space- the record, set 46 years ago, is still holding, it was made by astronauts who took part in the Apollo 10 mission. Having circled the moon, they returned back when spaceship speed in space was 39,897 km/h. In the near future, it is planned to send the Orion spacecraft into weightlessness, which will put astronauts into low Earth orbit. Perhaps then it will be possible to break the 46-year-old record. The speed of light in space- 1 billion km / h. I wonder if we can overcome such a distance with our maximum available speed of 40,000 km / h. Here what is the speed in space develops near the light, but we do not feel it here.

Theoretically, a person can move at a speed slightly less than the speed of light. However, this will entail enormous harm, especially for an unprepared organism. Indeed, to begin with, such a speed must be developed, an effort must be made to safely reduce it. Because rapid acceleration and deceleration can be fatal to a person.

In ancient times, it was believed that the Earth was motionless, no one was interested in the question of the speed of its rotation in orbit, because such concepts did not exist in principle. But even now it is difficult to give an unambiguous answer to the question, because the value is not the same in different geographical points. Closer to the equator, the speed will be higher, in the region of southern Europe it is 1200 km / h, this is the average Earth's speed in space.

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

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

In the solar system, hundreds of thousands of asteroids have been discovered. Some reach over 500 kilometers in diameter. Larger masses take on a spherical shape and begin to be classified by scientists as dwarf planets. The speed of asteroids is limited by their presence in the solar system, they revolve around the sun. Pallas - 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 to three times. The name of the asteroids is the date of their discovery (1959 LM, 1997 VG). After studying, calculating the orbit, the object can get its own name.

Heavenly bodies inevitably collide with each other. The moon has preserved the result of millions and millions of years of interaction. On earth, huge craters indicate that once upon a time, 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 energy of the explosion is simply dissipated in space. It is extremely important to detect a dangerous block as early as possible, which is not always possible. The good news 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 meteoroids burn out, the so-called "shooting stars". Every 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, the speed drops sharply. In general, information about the speed of meteorites is blurred. Limits are given from 11 to 72 kilometers per second for meteorites of the solar system, stray from the outside develop an order of magnitude greater speed.

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

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

3. FLIGHT OF METEORS IN THE EARTH'S ATMOSPHERE

Meteors appear at altitudes of 130 km and below and usually disappear around an altitude of 75 km. These boundaries change depending on the mass and speed of meteoroids penetrating the atmosphere. Visual determinations of the heights of meteors from two or more points (the so-called corresponding ones) refer mainly to meteors of 0-3rd magnitude. Taking into account the influence of fairly significant errors, visual observations give the following meteor heights: H1= 130-100 km, disappearance height H2= 90 - 75 km, midway height H0= 110 - 90 km (Fig. 8).

Rice. 8. Heights ( H) meteor phenomena. Height limits(left): the beginning and end of the path of fireballs ( B), meteors according to visual observations ( M) and from radar observations ( RM), telescopic meteors according to visual observations ( T); (M T) - area of delay of meteorites. Distribution curves(on right): 1 - the middle of the path of meteors according to radar observations, 2 - the same according to photographic data, 2a And 2b- the beginning and end of the path according to photographic data.

Much more accurate photographic measurements of heights tend to refer to brighter meteors, from -5th to 2nd magnitude, or to the brightest parts of their trajectories. According to photographic observations in the USSR, the heights of bright meteors are within the following limits: H1= 110-68 km, H2= 100-55 km, H 0= 105-60 km. Radar observations make it possible to determine separately H1 And H2 only for the brightest meteors. According to radar data for these objects H1= 115-100 km, H2= 85-75 km. It should be noted that the radar determination of the height of meteors refers only to that part of the meteor trajectory along which a sufficiently intense ionization trail is formed. Therefore, for the same meteor, the height according to photographic data can differ markedly from the height according to radar data.

For weaker meteors, with the help of radar, it is possible to determine statistically only their average height. The distribution of average heights of meteors of predominantly 1-6th magnitude, obtained by the radar method, is shown below:

Considering the factual material on determining the heights of meteors, it can be established that, according to all the data, the vast majority of these objects are observed in the altitude zone of 110-80 km. In the same zone, telescopic meteors are observed, which, according to A.M. Bakharev have heights H1= 100 km, H2= 70 km. However, according to telescopic observations by I.S. Astapovich and his colleagues in Ashgabat, a significant number of telescopic meteors are also observed below 75 km, mainly at altitudes of 60-40 km. These are, apparently, slow and therefore weak meteors, which begin to glow only after deeply crashing into the earth's atmosphere.

Moving on to very large objects, we find that fireballs appear at altitudes H1= 135-90 km, having the height of the end point of the path H2= 80-20 km. Fireballs penetrating the atmosphere below 55 km are accompanied by sound effects, and reaching a height of 25-20 km usually precede the fall of meteorites.

The heights of meteors depend not only on their mass, but also on their speed relative to the Earth, or the so-called geocentric speed. The greater the speed of the meteor, the higher it begins to glow, since a fast meteor, even in a rarefied atmosphere, collides with air particles much more often than a slow one. The average height of meteors depends on their geocentric velocity as follows (Fig. 9):

Geocentric speed ( Vg)	20	30	40	50	60	70 km/s
Average height ( H0)	68	77	82	85	87	90 km

With the same geocentric velocity of meteors, their heights depend on the mass of the meteoroid. The greater the mass of the meteor, the lower it penetrates.

The visible part of the meteor's trajectory, i.e. the length of its path in the atmosphere is determined by the heights of its appearance and disappearance, as well as the inclination of the trajectory to the horizon. The steeper the slope of the trajectory to the horizon, the shorter the apparent path length. The path length of ordinary meteors, as a rule, does not exceed several tens of kilometers, but for very bright meteors and fireballs it reaches hundreds, and sometimes thousands of kilometers.

Rice. 10. Zenith attraction of meteors.

Meteors glow on a short visible segment of their trajectory in the earth's atmosphere, several tens of kilometers long, which they fly over in a few tenths of a second (less often, in a few seconds). On this segment of the meteor's trajectory, the effect of the Earth's attraction and deceleration in the atmosphere is already manifested. When approaching the Earth, the initial speed of the meteor under the influence of gravity increases, and the path is curved so that its observed radiant shifts to the zenith (the zenith is a point above the observer's head). Therefore, the effect of the Earth's gravity on meteoric bodies is called zenith attraction (Fig. 10).

The slower the meteor, the greater the effect of zenithal gravity, as can be seen from the following table, where V g denotes the initial geocentric velocity, V" g- the same speed, distorted by the attraction of the Earth, and Δz- maximum value of zenith attraction:

V g	10	20	30	40	50	60	70 km/s
V" g	15,0	22,9	32,0	41,5	51,2	61,0	70.9 km/s
Δz	23o	8o	4o	2o	1o	<1 o

Penetrating into the Earth's atmosphere, the meteoroid experiences, in addition, deceleration, at first almost imperceptible, but very significant at the end of the path. According to Soviet and Czechoslovak photographic observations, deceleration can reach 30-100 km/sec 2 in the final segment of the trajectory, while deceleration varies from 0 to 10 km/sec 2 along most of the trajectory. Slow meteors experience the greatest relative velocity loss in the atmosphere.

The apparent geocentric velocity of meteors, distorted by zenithal attraction and deceleration, is corrected accordingly, taking into account the influence of these factors. For a long time, the velocities of meteors were not known accurately enough, since they were determined from low-precision visual observations.

The photographic method for determining the speed of meteors using an obturator is the most accurate. Without exception, all determinations of the speed of meteors, obtained by photographic means in the USSR, Czechoslovakia, and the USA, show that meteoroids must move around the Sun along closed elliptical paths (orbits). Thus, it turns out that the overwhelming part of meteoric matter, if not all of it, belongs to the solar system. This result is in excellent agreement with the data of radar measurements, although the photographic results refer, on average, to brighter meteors, i.e. to larger meteoroids. The distribution curve of meteor velocities found using radar observations (Fig. 11) shows that the geocentric velocity of meteors lies mainly in the range from 15 to 70 km/s (some speed determinations exceeding 70 km/s are due to the inevitable errors of observations ). This once again confirms the conclusion that meteoric bodies move around the Sun in ellipses.

The fact is that the speed of the Earth's orbit is 30 km / s. Therefore, oncoming meteors with a geocentric velocity of 70 km/sec move relative to the Sun at a speed of 40 km/sec. But at Earth's distance, the parabolic speed (ie, the speed required for a body to parabola out of the solar system) is 42 km/sec. This means that all meteor velocities do not exceed parabolic and, consequently, their orbits are closed ellipses.

The kinetic energy of meteoroids entering the atmosphere with a very high initial velocity is very high. Mutual collisions of molecules and atoms of a meteor and air intensively ionize gases in a large volume of space around a flying meteoroid. Particles torn out in abundance from the meteoric body form around it a brightly luminous shell of incandescent vapors. The glow of these vapors resembles the glow of an electric arc. The atmosphere at altitudes where meteors appear is very rarefied, so the process of reunion of electrons torn off from atoms continues for quite a long time, causing the glow of a column of ionized gas, which lasts for several seconds, and sometimes minutes. Such is the nature of the self-luminous ionization trails that can be observed in the sky after many meteors. The trace glow spectrum also consists of lines of the same elements as the spectrum of the meteor itself, but already neutral, not ionized. In addition, atmospheric gases also glow in the traces. This is indicated by the open in 1952-1953. in the spectra of the meteor trail, the lines of oxygen and nitrogen.

The spectra of meteors show that meteor particles either consist of iron, having a density of more than 8 g/cm 3 , or are stony, which should correspond to a density of 2 to 4 g/cm 3 . The brightness and spectrum of meteors make it possible to estimate their size and mass. The apparent radius of the luminous shell of meteors of 1-3rd magnitude is estimated at about 1-10 cm. However, the radius of the luminous shell, determined by the expansion of luminous particles, is much greater than the radius of the meteor body itself. Meteor bodies flying into the atmosphere at a speed of 40-50 km / s and creating the phenomenon of meteors of zero magnitude have a radius of about 3 mm, and a mass of about 1 g. The brightness of meteors is proportional to their mass, so that the mass of a meteor of some magnitude is 2, 5 times less than for meteors of the previous magnitude. In addition, the brightness of meteors is proportional to the cube of their speed relative to the Earth.

Entering the Earth's atmosphere with a high initial velocity, meteor particles are encountered at altitudes of 80 km or more with a very rarefied gaseous medium. The air density here is hundreds of millions of times less than at the surface of the Earth. Therefore, in this zone, the interaction of the meteoroid with the atmospheric environment is expressed in the bombardment of the body by individual molecules and atoms. These are molecules and atoms of oxygen and nitrogen, since the chemical composition of the atmosphere in the meteor zone is approximately the same as at sea level. Atoms and molecules of atmospheric gases during elastic collisions either bounce off or penetrate into the crystal lattice of a meteoric body. The latter quickly heats up, melts and evaporates. The particle evaporation rate is initially insignificant, then increases to a maximum and decreases again towards the end of the meteor's visible path. Evaporating atoms fly out of the meteor at speeds of several kilometers per second and, having high energy, experience frequent collisions with air atoms, leading to heating and ionization. A hot cloud of evaporated atoms forms a luminous shell of a meteor. Some of the atoms completely lose their outer electrons during collisions, as a result of which a column of ionized gas with a large number of free electrons and positive ions is formed around the trajectory of the meteor. The number of electrons in the ionized trace is 10 10 -10 12 per 1 cm of the path. The initial kinetic energy is spent on heating, luminescence and ionization approximately in the ratio of 10 6:10 4:1.

The deeper the meteor penetrates into the atmosphere, the denser its incandescent shell becomes. Like a very fast-moving projectile, the meteor forms a bow shock wave; this wave accompanies the meteor as it moves in the lower layers of the atmosphere, and causes sound phenomena in the layers below 55 km.

Traces left after the flight of meteors can be observed both with the help of radar and visually. Ionization traces of meteors can be observed especially successfully with high-aperture binoculars or telescopes (the so-called comet detectors).

The trails of fireballs penetrating into the lower and denser layers of the atmosphere, on the contrary, are mainly composed of dust particles and therefore are visible as dark smoky clouds against the blue sky. If such a dust trail is illuminated by the rays of the setting Sun or Moon, it is visible as silvery stripes against the background of the night sky (Fig. 12). Such traces can be observed for hours until they are destroyed by air currents. Traces of less bright meteors, formed at altitudes of 75 km or more, contain only a very small fraction of dust particles and are visible only due to self-glow of ionized gas atoms. The duration of the visibility of the ionization trail with the naked eye is on average 120 seconds for bolides of -6th magnitude, and 0.1 seconds for a meteor of 2nd magnitude, while the duration of the radio echo for the same objects (at a geocentric velocity of 60 km/sec) is equal to 1000 and 0.5 sec. respectively. The extinction of ionization traces is partly due to the addition of free electrons to oxygen molecules (O 2) contained in the upper atmosphere.

The most well studied among the small bodies of the solar system are asteroids - small planets. The history of their study has almost two centuries. Back in 1766, an empirical law was formulated that determines the average distance of a planet from the Sun, depending on the ordinal number of this planet. In honor of the astronomers who formulated this law, he received the name: "the law of Titius - Bode." a = 0.3*2k + 0.4 from the sun).

At first, astronomers, preserving the traditions of the ancients, assigned the names of gods to minor planets, both Greco-Roman and others. By the beginning of the 20th century, the names of almost all the gods known to mankind appeared in the sky - Greco-Roman, Slavic, Chinese, Scandinavian, and even the gods of the Mayan people. 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 arose of streamlining the procedure for this astronomical canonization of names. This question is all the more serious because, unlike the perpetuation of memory on Earth (names of streets, cities, etc.), the name of an asteroid cannot be changed. Since its inception (July 25, 1919), the International Astronomical Union (IAU) has been doing this.

The semi-major axes of the orbits of the main part of the asteroids are in the range from 2.06 to 4.09 AU. e., and the average value is 2.77 a. e. The average eccentricity of the orbits of small planets is 0.14, the average inclination of the plane of the asteroid's orbit to the plane of the Earth's orbit is 9.5 degrees. The speed of movement 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 main-belt asteroid, generally speaking, passes near the Earth's orbit. However, in 1932 the first asteroid was discovered, the orbit of which had a perihelion distance less than the radius of the Earth's orbit. In principle, its orbit allowed for the possibility of an asteroid approaching the Earth. This asteroid was soon "lost" and rediscovered in 1973. It received the number 1862 and the name Apollo. In 1936, the asteroid Adonis flew at a distance of 2 million km from the Earth, and in 1937, the asteroid Hermes flew at a distance of 750,000 km from the Earth. Hermes has a diameter of almost 1.5 km, and was discovered only 3 months before its closest approach to the Earth. After the flyby of Hermes, astronomers began to realize the scientific problem of the asteroid hazard. To date, about 2000 asteroids are known, the orbits of which allow them to approach the Earth. Such asteroids are called near-Earth asteroids.

According to their physical characteristics, asteroids are divided into several groups, within which objects have similar reflective surface properties. Such groups are called taxonomic (taxonometric) classes or types. The table lists 8 main main taxonomic types: C, S, M, E, R, Q, V and A. Each class of asteroids corresponds to meteorites having 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 are determined by radar as they pass near the Earth. Some of them look like main belt asteroids, but most of them are less regular. For example, the asteroid Toutatis consists of two, and 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: so far there are no known asteroids, about which it can be said that in the next hundred years they will come close to the Earth. The nearest will be the passage of the asteroid Hathor in 2086 at a distance of 883 thousand km.

To date, a number of asteroids have passed at distances much smaller than those given above. They were discovered during their next passages. Thus, while the main danger is not yet discovered asteroids.