Planets meteorites comets. The most common point of view is that planets are fragments of small planets. A meteorite is a solid body of cosmic origin that fell to the surface of the Earth. Most meteorites found weigh between

Minor planets - asteroids (Greek asteroideis – star-like) have nothing in common with stars, and are named so only because they are visible through a telescope as point objects. Interesting history of the discovery of small

planets. By the end of the 18th century. the empirical law of planetary distances was known (the so-called Titius-Bode rule), according to which there should have been another unknown planet between Mars and Jupiter

nope. The search for it led the astronomer Piazzi to the discovery in 1801 of the planet Ceres with a diameter of 1003 km. The discovery of three more planets: Palladas - 608 km, Juno - 180 km and Vesta - 538 km - was unexpected. In recent years, asteroids up to 1 km in diameter have been discovered, and their total number reaches several thousand. Since asteroids move, during long photographic exposures they appear as bright white lines against a black background of the starry sky.

Observations have shown that asteroids have an irregular polyhedral shape and move in orbits of various shapes - from circles to highly elongated ellipses; the vast majority of them (98%) are contained between the orbits of Mars and Jupiter (“the main asteroid belt”), but the asteroid Icarus approaches the Sun closer than Mercury, and some move away as far as Saturn. The orbits of most asteroids are concentrated near the ecliptic plane; their circulation periods range from 3.5 to 6 years; they are assumed to rotate around their axes (based on the periodic change in apparent brightness). Based on their material composition, asteroids are divided into stony, carbonaceous and metallic asteroids.

The total mass of all asteroids is estimated at 0.01 Earth masses. Their common attraction does not cause noticeable disturbances in the movement of Mars and other planets.

The orbits of some asteroids intersect with the orbit of the Earth, but the probability of the Earth and an asteroid simultaneously being at the same point and colliding is extremely small. It is believed that 65 million years ago, a celestial body such as an asteroid fell to Earth in the area of the Yucatan Peninsula and its fall caused clouding of the atmosphere and a sharp decrease in the average annual air temperature, which affected the Earth's ecosystem.

Currently, astronomers are concerned about the unusual “invasion” of large celestial bodies in the vicinity of the planets of the solar system. Thus, in May 1996, two asteroids flew at a short distance from the Earth. Many experts suggest that the solar system was caught in a kind of trail of large celestial bodies formed outside our system, and therefore believe that, along with the nuclear threat, the number one danger to our planet has become the danger posed by asteroids. A new important problem has arisen - the creation of space protection of the Earth from asteroids, which should include both ground-based and space-based assets, including those located in deep space. Created

The development of such a system should be carried out on an international basis.

On the other hand, the increase in the number of visible asteroids can be explained by an increase in the volume of astronomical information in last years, after the observations were transferred from the surface of the Earth to near Space.

On the issue of the origin of asteroids, two directly opposing points of view have been expressed. According to one hypothesis, asteroids are fragments of a large planet (it was called Phaethon), located between Mars and Jupiter at the site of the main asteroid belt and split apart as a result of a cosmic catastrophe due to the powerful gravitational influence of Jupiter. According to another hypothesis, asteroids are protoplanetary bodies that arose due to the thickening of the dust environment, which could not unite into a planet due to the disturbing action of Jupiter. In both cases, the “culprit” turns out to be Jupiter.

Comets(Greek 1gote1e5- long-haired) - small bodies solar system, moving along highly elongated elliptical or even parabolic orbits. Some comets have perihelia near the Sun and aphelion outside Pluto. The movement of comets in orbits can be either forward or backward. The planes of their orbits lie in different directions from the Sun. The orbital periods of comets vary greatly: from several years to many thousands of years. Tenth part famous comets(about 40) appeared several times; they are called periodic.

Comets have a head and a tail. The head consists of a hard core and coma. The core is an ice conglomerate of frozen gases (water vapor, carbon dioxide, methane, ammonia, etc.) with an admixture of refractory silicates, carbon dioxide and metal particles - iron, manganese, nickel, sodium, magnesium, calcium, etc. It is assumed that the core contains organic molecules. Comet nuclei are small, their diameter ranges from several hundred meters to several (50-70) kilometers. Coma is a gas-dust environment (hydrogen, oxygen, etc.), glowing when approaching the Sun. Near perihelion, from the comet’s nucleus, under the influence of solar heat and corpuscular flows, “evaporation” (sublimation) of frozen gases occurs and a luminous tail of the comet is formed, sometimes more than one. It consists of rarefied gases and small solid particles and is directed in the direction opposite to the Sun. The length of the tails reaches hundreds of millions of kilometers. The Earth has been caught in the tails of comets more than once, for example in 1910. This caused great concern among people then, although there was no danger to the Earth.

falling into cometary tails is not an idea: they are so rarefied that the admixture of poisonous gases contained in cometary tails (methane, cyanogen) in the atmosphere is imperceptible.

Among periodic comets, the most interesting is Halley's comet, named after the English astronomer who discovered it in 1682 and calculated its orbital period (about 76 years). It was in its tail that the Earth found itself in 1910. The last time it appeared in the sky was in April 1986, passing at a distance of 62 million km from the Earth. Careful studies of the comet using spacecraft showed that the icy core of the comet is a monolithic body of irregular shape measuring about 15x7 km, around which a giant hydrogen corona with a diameter of 10 million km was discovered.

Comets are short-lived celestial bodies, since as they approach the Sun they gradually “melt” due to the intense outflow of gases or break up into a swarm of meteors. The meteoric material is subsequently more or less evenly distributed throughout the entire orbit of the parent comet. In this regard, the history of the periodic (about 7 years) comet Bijela, discovered in 1826, is interesting. Twice after its discovery, astronomers observed its appearance, and the third time, in 1846, they managed to record its division into two parts, which, on subsequent returns They were moving further and further away from each other. Then meteoric substance The comet stretched across its entire orbit, during which the Earth crossed an abundant “rain” of meteors.

There is no precise evidence that the Earth has ever collided with a comet nucleus. No more than five comets penetrate into Earth's orbit each year. However, there is a version that the famous Tunguska “meteorite”, which fell in 1908 in the basin of the Pod-Kamennaya Tunguska River, near the village of Vanavara, is a small (about 30 m) fragment of the nucleus of comet Encke, which exploded as a result of thermal heating in the atmosphere, and “ice” and solid impurities “evaporated.” At the same time explosive air wave forest was felled over an area within a radius of 30 km.

In 1994, scientists observed the fall of Comet Shoemaker-Levy onto Jupiter. At the same time, it broke up into dozens of fragments 3-4 km in diameter, which flew one after another at enormous speed - about 70 km/s, exploded in the atmosphere and evaporated. The explosions created a gigantic hot cloud 20 thousand km in size and with a temperature of 30,000 °C. The fall of such a comet to Earth would end in a cosmic catastrophe.

It is believed that the “comet cloud” surrounding the Sun formed along with the Solar System. Therefore, by studying the material of comets, scientists obtain information about the primary material from which planets and satellites were formed. In addition, assumptions have been made about the “participation” of comets in the origin of life on Earth, since radio spectroscopic methods have proven the presence of complex organic compounds (formaldehyde, cyanoacetylene, etc.) in comets and meteorites.

Meteors, usually called “shooting stars”, are tiny (mg) solid particles that fly into the atmosphere at speeds of up to 50-60 km/s, heat up due to friction with the air to several thousand degrees Celsius, ionize gas molecules, causing them to emit light, and evaporate at an altitude of 80-100 km above the earth's surface. Sometimes a large and exceptionally bright fireball appears in the sky, which can break apart and even explode during flight. Such a meteor is called fireball. A similar fireball exploded on September 25, 2002 in Irkutsk region, between the villages of Mama and Bodaibo. In the sky, both individual meteors appearing randomly in the sky, and groups of meteors in the form of meteor showers, within which particles move parallel to each other, although in perspective it seems that they are scattering from one point in the sky, called radiant. Meteor showers are named by the constellations in which their radiants are located. The Earth crosses the orbit of the Perseids around August 12, the Orionids - October 20, the Leonids - November 18, etc. Meteor showers move along the orbits of those asteroids or comets, as a result of the disintegration of which they are formed. The orbits of meteor showers are carefully studied for the safety of spacecraft and vehicles.

Meteorites(from Greek te1eoga- celestial phenomena) are large meteoroids that fall to Earth. Every year, about two thousand meteorites with a total mass of about 20 tons fall onto the earth's surface. They are fragments of a rounded angular shape, usually covered with a thin black melting crust with numerous cells from the drilling action of air jets. According to their structure, they are of three classes: iron, consisting mainly of nickel iron, stone, which contain predominantly silicate minerals, and iron-stone, consisting of a mixture of these substances. There are two groups of rocks: chondrites (granular meteorites) and

Ironstone 1 ,5%

Iron

achondrites (earthy meteorites). Stony meteorites predominate (Fig. 3). Physico-chemical analysis of meteorites indicates that they consist of chemical elements and their isotopes known on Earth, which confirms the unity of matter in the Universe.

The largest Goba meteorite, measuring 2.75x2.43 m and weighing 59 tons, was found in southwest Africa; it is iron. The Sikhote-Alin meteorite (fell in 1947) split into thousands of pieces in the air and fell to Earth as “iron rain.” The total weight of the collected fragments is about 23 tons, they created 24 impact craters ranging from 8 to 26 m in diameter. The Kaaba meteorite (“Black Stone”) is kept in the Mecca mosque in Saudi Arabia and serves as an object of worship for Muslims. Many meteorites have been discovered in Antarctica, and they are also found in the sediments of the floor of the World Ocean.

Rice. 3. a- relative frequency of meteorite falls different classes(according to J. Bud); b - mineral composition of a typical chondrite (according to V. E. Khain)

At the dawn of the Earth's existence, when there was still a lot of unused material in the solar system, and the Earth's atmosphere - protection from meteorites - was still very thin, the number of meteorites bombarding the Earth was enormous and its surface resembled the face of the Moon. With time most of craters were destroyed by tectonic and exogenous processes, but many of them were still preserved in the form of ring-shaped geological structures called astroblemes(“star scars”). They are especially visible from space. They reach tens of kilometers in diameter. The study of meteorites allows us to judge the structure and properties of celestial bodies and supplements our information about the internal structure of the Earth.

Moon

The Earth is often, and not without reason, called the double planet Earth-Moon. Moon (Selena, in Greek mythology the Moon Goddess), our celestial neighbor, was the first to be directly studied.

General information about the moon. Movements of the Moon. The Moon is a natural satellite of the Earth, located at a distance of 384 thousand km (60 radii of the Earth). The average radius of the Moon is 1738 km (almost 4 times less than the Earth's). The Moon's mass is 1/81 that of the Earth, which is significantly greater than similar ratios for other planets in the Solar System (except for the Pluto-Charon pair); therefore, the Earth-Moon system is considered a double planet. It has a common center of gravity - the so-called barycenter, which is located in the body of the Earth at a distance of 0.73 radii from its center (1700 km from the surface of the Ocean).

Both components of the system rotate around this center, and it is the barycenter that moves in orbit around the Sun. The average density of lunar substance is 3.3 g/cm 3 (terrestrial - 5.5 g/cm 3). Volume of the Moon 50 times smaller than Earth. The force of lunar gravity is 6 times weaker than the earth's. The moon rotates around its axis, which is why it is slightly flattened at the poles. The axis of rotation of the Moon makes an angle of 83°22" with the plane of the lunar orbit. The plane of the Moon's orbit does not coincide with the plane of the Earth's orbit and is inclined to it at an angle of 5°9". The intersection of the orbits of the Earth and the Moon is called nodes of the lunar orbit.

The orbit of the Moon is an ellipse, in one of the foci of which the Earth is located, therefore the distance from the Moon to the Earth varies from 356 to 406 thousand km. The orbital period of the Moon and the corresponding

Rice. 4. Moon phases

exactly the same position of the Moon on the celestial sphere is called sidereal(sidereal) month (lat. sidus, sideris(genus) - star). It is 27.3 Earth days. The sidereal month coincides with the period of the daily rotation of the Moon around its axis due to their identical angular speed (= 13.2° per day), established due to the braking effect of the Earth. Due to the synchronicity of these movements, the Moon always faces us with one side. However, we see almost 60% of its surface thanks to libration- to the seeming-

A meteorite that fell on Friday, February 15, 2013 in Chelyabinsk led to many questions.

According to the data, a meteorite with a diameter of about 15 meters and weighing 7,000 tons entered the atmosphere at an angle of about 20 degrees at a speed of 65,000 km per hour. It passed through the atmosphere for 30 seconds before breaking apart. This resulted in an explosion approximately 20 km above the ground, producing a shock wave of 300 kilotons. As a result, more than 1000 people were injured.

Meteorite fragments were recently found near Lake Chebarkul.

Events such as the fall of a meteorite once again remind us of the potential danger that exists in outer space. What are a meteorite, an asteroid and a comet? How often do such events occur and can they be prevented?

Meteor falling

Meteor, meteorite, meteoroid - what's the difference?

A meteor is the scientific name for a "shooting star" and is the glowing trail of space debris that ends up in the Earth's atmosphere. They can be small as a grain of sand and large meteoroids up to 10-30 meters in size. As a rule, they burn up in the atmosphere, and those that fall to Earth are called meteorites.

How often does a meteorite fall to Earth?

Small drops happen every few months, but we don't see them. The thing is that two-thirds of the Earth is oceans, so we often miss these events. Such large objects as the one that exploded in Chelyabinsk occur much less frequently, approximately every five years. So in 2008, a similar event was observed in Sudan, but no one was hurt.

A meteorite is flying to Earth: can it be prevented?

As a rule, such meteoroids go undetected because most telescopes are aimed at identifying huge, potentially dangerous asteroids. There is no weapon yet that can prevent the fall of a meteorite or asteroid.

Asteroid impact

The Chelyabinsk meteorite was the largest since the 1908 Tunguska meteorite in Siberia, which was caused by an object roughly the size of asteroid 2012 DA14, which safely passed within a minimum distance of 27,000 km from Earth on February 15, 2013.

Asteroid Passage: What is an asteroid?

An asteroid is a celestial body that orbits the Sun, usually between Mars and Jupiter. Asteroids are also called space debris or fragments left behind when the solar system was formed.

Because of the collisions, some asteroids are ejected from the main belt, and they end up on a trajectory that intersects the Earth's orbit.

Large asteroids are called planetoids, and objects smaller than 30 meters are called meteoroids.

Asteroid sizes: how big can they be?

Asteroid 2012 DA14, which flew by on Friday, was about 45 meters in diameter and weighed about 130,000 tons. Scientists believe there are about 500,000 asteroids the size of asteroid 2012 DA14. However, less than one percent of asteroids have been discovered so far.

The supposed asteroid that killed the dinosaurs 65 million years ago is believed to have been around 10-15 km in diameter. If an asteroid of this magnitude were to fall today, it would wipe out all modern civilization.

Statistically, asteroids larger than 50 meters fall to Earth once a century. Asteroids larger than 1 km in diameter can collide every 100 thousand years.

Comet crash

2013 can be called the year of comets, as we will be able to observe two of the brightest comets in history at once.

What is a comet?

Comets are celestial bodies in our solar system, consisting of ice, dust and gas. Most of them are located in the Oort Cloud, a mysterious region of the outer edge of the solar system. Periodically they pass close to the Sun and begin to evaporate. The solar wind turns this steam into a huge tail.

Most comets are too far from the Sun and Earth to be seen with the naked eye. Bright comets appear every few years, and it is even rarer for two comets to appear in one year.

Comet 2013

Comet PANSTARRS

Comet PANSTARRS or C/2011 L4 was discovered in June 2011 using the Pan-STARRS 1 telescope located on the summit of Haleakala in Hawaii. In March 2013, the comet will be closest to the Sun (45,000 km) and the Earth (164 million km).

Although comet PANSTARRS was a dim and distant object at the time of its discovery, it has steadily become brighter since then.

Comet ISON, discovered in 2012

When can you watch? Mid November – December 2013

Comet ISON or C/2012 S1 was discovered on September 21, 2012 by two astronomers Vitaly Nevsky and Artem Novichonok using a telescope International Scientific Optical Network(ISON).

Orbital calculations showed that comet ISON will make its closest approach to the Sun at a distance of 1.2 million km. The comet will be bright enough to be visible in the sky at its closest approach to the Sun in the first weeks of November.

It is believed that this comet will be brighter than the full Moon and will be visible even during the day.

Comet Impact

Could a comet collide with Earth? It is known from history that the comet Shoemaker-Levi 9 collided with Jupiter in July 1994, and it became the first comet collision observed by scientists. Considering that this happened on an uninhabited planet, the event became more likely interesting example destructive forces of the Universe. However, if this had happened on Earth, history would have taken a completely different turn.

Comets and asteroids

Comets differ from asteroids in that they have an unusually elongated elliptical orbit, meaning they move very large distances from the Sun. On the contrary, asteroids remain within the asteroid belt.

Fortunately, it takes many years to pass the comet's orbit. A comet approaches Earth once every 200,000 years. To date, there are no known comets that pose a threat to our planet in the near future.

Comets with an orbital period greater than 200,000 years have a less predictable orbit and, although there is little chance of colliding with Earth, they should not be forgotten.

Asteroids. Meteorites. Meteors.

Asteroid

ASTEROID is a small planet-like celestial body in the Solar System moving in orbit around the Sun. Asteroids, also known as minor planets, are significantly smaller in size than planets.

Definitions.

The term asteroid (from ancient Greek - “like a star”) was introduced by William Herschel on the basis that these objects, when observed through a telescope, looked like points of stars - in contrast to planets, which when observed through a telescope, looked like disks. The exact definition of the term "asteroid" is still not established. The term “minor planet” (or “planetoid”) is not suitable for defining asteroids, since it also indicates the location of the object in the Solar System. However, not all asteroids are minor planets.

One way to classify asteroids is by size. The current classification defines asteroids as objects with a diameter greater than 50 m, separating them from meteoroids, which look like large rocks or may be even smaller. The classification is based on the assertion that asteroids can survive entry into the Earth's atmosphere and reach its surface, while meteors, as a rule, burn up completely in the atmosphere.

As a result, an “asteroid” can be defined as a solar system object made of solid materials that is larger than a meteor.

Asteroids in the Solar System

To date, tens of thousands of asteroids have been discovered in the Solar System. As of September 26, 2006, there were 385,083 objects in the databases, 164,612 had precisely defined orbits and were assigned an official number. 14,077 of them at this time had officially approved names. It is estimated that the Solar System may contain from 1.1 to 1.9 million objects larger than 1 km. Most known on this moment asteroids are concentrated within the asteroid belt, located between the orbits of Mars and Jupiter.

Ceres, measuring approximately 975×909 km, was considered the largest asteroid in the Solar System, but since August 24, 2006, it received the status of a dwarf planet. The other two largest asteroids, 2 Pallas and 4 Vesta, have a diameter of ~500 km. 4 Vesta is the only object in the asteroid belt that can be observed with the naked eye. Asteroids moving in other orbits can also be observed during their passage near the Earth (for example, 99942 Apophis).

The total mass of all main belt asteroids is estimated at 3.0-3.6×1021 kg, which is only about 4% of the mass of the Moon. The mass of Ceres is 0.95 × 1021 kg, that is, about 32% of the total, and together with the three largest asteroids 4 Vesta (9%), 2 Pallas (7%), 10 Hygea (3%) - 51%, that is, the absolute majority asteroids have negligible mass.

Asteroid exploration

The study of asteroids began after the discovery of the planet Uranus in 1781 by William Herschel. Its average heliocentric distance turned out to correspond to the Titius-Bode rule.

At the end of the 18th century, Franz Xaver von Zach organized a group that included 24 astronomers. Since 1789, this group has been searching for a planet that, according to the Titius-Bode rule, should be located at a distance of about 2.8 astronomical units from the Sun - between the orbits of Mars and Jupiter. The task was to describe the coordinates of all stars in the area of zodiacal constellations at a certain moment. On subsequent nights, the coordinates were checked and objects that had moved greater distances were identified. The estimated displacement of the desired planet should have been about 30 arcseconds per hour, which should have been easy to notice.

Ironically, the first asteroid, 1 Ceres, was discovered by accident by the Italian Piazzi, who was not involved in this project, in 1801, on the first night of the century. Three others - 2 Pallas, 3 Juno and 4 Vesta - were discovered over the next few years - the last, Vesta, in 1807. After another 8 years of fruitless searching, most astronomers decided that there was nothing more there and stopped research.

However, Karl Ludwig Henke persisted, and in 1830 he resumed the search for new asteroids. Five years later, he discovered Astraea, the first new asteroid in 38 years. He also discovered Hebe less than two years later. After this, other astronomers joined the search, and then at least one new asteroid was discovered per year (with the exception of 1945).

In 1891, Max Wolf was the first to use the astrophotography method to search for asteroids, in which asteroids left short light lines in photographs with a long exposure period. This method significantly increased the number of detections compared to previously used visual observation methods: Wolff single-handedly discovered 248 asteroids, starting with 323 Brutius, while little more than 300 had been discovered before him. Now, a century later, only a few thousand asteroids have been identified, numbered and named. There are many more of them known, but scientists are not very worried about studying them, calling asteroids the “vermin of the skies.”

Asteroid naming

At first, the asteroids were given the names of heroes of Roman and Greek mythology, later the discoverers received the right to call it whatever they wanted, for example, by their own name. At first, asteroids were given predominantly female names; only asteroids with unusual orbits (for example, Icarus, approaching the Sun closer than Mercury) received male names. Later, this rule was no longer observed.

Not any asteroid can receive a name, but only one whose orbit has been more or less reliably calculated. There have been cases when an asteroid received a name decades after its discovery. Until the orbit is calculated, the asteroid is given a serial number reflecting the date of its discovery, for example, 1950 DA. The numbers indicate the year, the first letter is the number of the crescent in the year in which the asteroid was discovered (in the example given, this is the second half of February). The second letter indicates the serial number of the asteroid in the specified crescent; in our example, the asteroid was discovered first. Since there are 24 crescents and 26 English letters, two letters are not used in the designation: I (due to the similarity with the unit) and Z. If the number of asteroids discovered during the crescent exceeds 24, they again return to the beginning of the alphabet, assigning the second the letter index is 2, the next time it returns - 3, etc.

After receiving a name, the official naming of the asteroid consists of a number (serial number) and a name - 1 Ceres, 8 Flora, etc.

Asteroid belt

The orbits of the majority of numbered minor planets (98%) are located between the orbits of the planets Mars and Jupiter. Their average distances from the Sun range from 2.2 to 3.6 AU. They form the so-called main asteroid belt. All small planets, like large ones, move in a forward direction. The periods of their revolution around the Sun range from three to nine years, depending on the distance. It is easy to calculate that the linear speed is approximately 20 km/s. The orbits of many small planets are noticeably elongated. Eccentricities rarely exceed 0.4, but, for example, for asteroid 2212 Hephaestus it is 0.8. Most orbits are located close to the ecliptic plane, i.e. to the plane of the Earth's orbit. Tilts are usually a few degrees, but there are exceptions. Thus, the orbit of Ceres has an inclination of 35°, and large inclinations are also known.

Perhaps, for us inhabitants of the Earth, it is most important to know the asteroids whose orbits are close to the orbit of our planet. There are usually three families of near-Earth asteroids. They are named after typical representatives - minor planets: 1221 Amur, 1862 Apollo, 2962 Aten. The Amur family includes asteroids whose orbits at perihelion almost touch the orbit of the Earth. The Apollo missions cross the Earth's orbit from the outside, their perhelion distance is less than 1 AU. "Atonans" have orbits with a semi-major axis smaller than the Earth's and intersect the Earth's orbit from the inside. Representatives of all these families can meet with the Earth. As for close passes, they happen quite often.

For example, the asteroid Amur at the time of discovery was 16.5 million kilometers from the Earth, 2101 Adonis approached by 1.5 million kilometers, 2340 Hathor - by 1.2 million kilometers. Astronomers at many observatories observed the passage of asteroid 4179 Tautatis past Earth. On December 8, 1992, he was 3.6 million kilometers away from us.

The majority of asteroids are concentrated in the main belt, but there are important exceptions. Long before the discovery of the first asteroid, the French mathematician Joseph Louis Lagrange studied the so-called three-body problem, i.e. investigated how three bodies move under the influence of gravity. The problem is very complex and in general terms has not yet been solved. However, Lagrange managed to find that in the system of three gravitating bodies (Sun - planet - small body) there are five points where the movement of the small body turns out to be stable. Two of these points are in the orbit of the planet, forming equilateral triangles with it and the Sun.

Many years later, already in the 20th century, theoretical constructions became reality. Near the Lagrangian points in the orbit of Jupiter, about two dozen asteroids were discovered, which were given the names of the heroes of the Trojan War. The “Greeks” asteroids (Achilles, Ajax, Odysseus, etc.) are 60° ahead of Jupiter, the “Trojans” follow at the same distance behind. It is estimated that the number of asteroids near Lagrange points can reach several hundred.

Dimensions and material composition

To find out the size of any astronomical object (if the distance to it is known), it is necessary to measure the angle at which it is visible from the Earth. However, it is no coincidence that asteroids are called minor planets. Even with large telescopes under excellent atmospheric conditions, using very complex, labor-intensive techniques, it is possible to obtain rather vague outlines of the disks of only a few of the largest asteroids. The photometric method turned out to be much more effective. There are very accurate instruments that measure gloss, i.e. stellar magnitude of the celestial body. In addition, the illumination created by the Sun on an asteroid is well known. All other things being equal, the brightness of an asteroid is determined by the area of its disk. It is, however, necessary to know what fraction of the light a given surface reflects. This reflectivity is called albedo. Methods have been developed for its determination by the polarization of asteroid light, as well as by the difference in brightness in the visible region of the spectrum and in the infrared range. As a result of measurements and calculations, the following sizes of the largest asteroids were obtained.

It is believed that there are three dozen asteroids with diameters of more than 200 km. Almost all of them are probably known. There are probably about 800 small planets with diameters from 80 to 200 km. With decreasing size, the number of asteroids increases rapidly. Photometric studies have shown that asteroids vary greatly in the degree of blackness of the material composing their surface. 52 Europe in particular has an albedo of 0.03. This corresponds to a dark substance similar in color to soot. Such dark asteroids are conventionally called carbonaceous (class C). Asteroids of another class are conventionally called stony (S), since they apparently resemble the deep rocks of the Earth. The albedo of S-asteroids is much higher. For example, at 44 Niza it reaches 0.38. This is the lightest asteroid. The study of reflection spectra and polarimetry made it possible to identify another class - metallic, or M-asteroids. Probably, on their surface there are outcrops of metal, for example nickel iron, like some meteorites.

Using very sensitive photometers, periodic changes in the brightness of asteroids were studied. The shape of the light curve can be used to judge the rotation period of the asteroid and the position of the rotation axis. The periods are very different - from several hours to hundreds of hours. Studying the light curve also allows us to draw certain conclusions about the shape of asteroids. Most of them have an irregular, clastic shape. Only the largest ones approach the ball.

The pattern of changes in the brightness of some asteroids suggests that they have satellites. Some of the minor planets may be close binary systems or even bodies rolling on each other's surfaces.

But reliable information about asteroids can only be obtained from close-range observations - from spacecraft. We already have such experience. On October 29, 1991, the American Galileo spacecraft transmitted an image of asteroid 951 Gaspra to Earth. The picture was taken from a distance of 16 thousand kilometers. It clearly shows the angular-smoothed shape of the asteroid and its cratered surface. We can confidently determine the dimensions: 12x16 km.

For a long time, no asteroids were known whose orbits lay entirely outside the orbit of Jupiter. But in 1977, such a small planet was discovered - this is 2060 Chiron. Observations have shown that its perihelion (the point of its orbit closest to the Sun) lies inside the orbit of Saturn, and its aphelion (the point of greatest removal) is almost at the very orbit of Uranus, on the distant, cold and dark outskirts of the planetary system. The distance to Chiron at perihelion is 8.51 AU, and at aphelion - 18.9 AU. More distant asteroids have also been discovered. It is assumed that they form a second, outer asteroid belt (Kuiper belt).

The brightest asteroid

The asteroid that appears the brightest from Earth is Vesta(4). When Vesta is at its closest possible distance from Earth, its brightness reaches magnitude 6.5. In very dark skies, Vesta can even be seen with the naked eye (it is the only asteroid that can be seen with the naked eye at all). The next brightest asteroid is Ceres, but its brightness never exceeds magnitude 7.3. Although Vesta is three-fifths the size of Ceres, it is much more reflective. Vesta reflects about 25% of the sunlight falling on it, while Ceres reflects only 5%. Vesta appears to be a light-colored volcanic rock that is highly reflective. Asteroids with this reflectivity belong to a separate class known as type E (the class designation comes from the name of the mineral enstatite). Such asteroids are rare, and their reflectivity ranges from 30 to 40%. The brightest of them, Nisa (44), has a magnitude of 9.7, although its diameter is only 68 km.

METEORITE

METEORITE - a piece of extraterrestrial matter that fell to the surface of the Earth; Literally, “stone from the sky.”

Meteorites are the oldest known minerals (4.5 billion years old), so they should preserve traces of the processes that accompanied the formation of the planets. Until samples of lunar soil were brought to Earth, meteorites remained the only samples of extraterrestrial matter. Geologists, chemists, physicists and metallurgists have been collecting and studying meteorites for more than 200 years. From these studies the science of meteorites emerged. Although the first reports of meteorite falls appeared a long time ago, scientists were very skeptical about them. Various facts led them to finally believe in the existence of meteorites. In 1800–1803 several famous European chemists reported that chemical composition"meteor rocks" from different places fall is similar, but different from the composition of earthly rocks. Finally, when in 1803 a terrible “rain of stones” broke out in Aigle (France), littering the ground with fragments and witnessed by many excited eyewitnesses, the French Academy of Sciences was forced to agree that these were indeed “stones from the sky.” It is now believed that meteorites are fragments of asteroids and comets.

Meteorites are divided into “fallen” and “found”. If a person saw a meteorite fall through the atmosphere and then actually found it on the ground (a rare event), then such a meteorite is called a "fallen". If it was found by chance and identified, which is typical for iron meteorites, then it is called “found.” Meteorites are named after the places where they were found. In some cases, not one, but several fragments are found. For example, after the 1912 meteor shower in Holbrook (Arizona), more than 20 thousand fragments were collected.

Meteorite fall. Until a meteorite reaches the Earth, it is called a meteoroid. Meteoroids fly into the atmosphere at speeds from 11 to 30 km/s. At an altitude of about 100 km, due to friction with the air, the meteoroid begins to heat up; its surface becomes hot, and a layer several millimeters thick melts and evaporates. At this time it is visible as a bright meteor (see METEOR). The molten and evaporated substance is continuously carried away by air pressure - this is called ablation. Sometimes, under the pressure of air, a meteor is crushed into many fragments. Passing through the atmosphere, it loses from 10 to 90% of its initial mass. However, the interior of the meteor usually remains cold, since it does not have time to warm up during the 10 seconds that the fall lasts. Overcoming air resistance, small meteorites significantly reduce their flight speed by the time they hit the ground and usually go deeper into the ground by no more than a meter, and sometimes they simply remain on the surface. Large meteorites are slowed down only slightly and upon impact produce an explosion with the formation of a crater, such as in Arizona or on the Moon. The largest meteorite found is the iron meteorite Goba (South Africa), whose weight is estimated at 60 tons. It was never moved from the place where it was found.

Every year, several meteorites are picked up immediately after their observed fall. In addition, more and more old meteorites are being discovered. In two places in the east of the state. In New Mexico, where the wind constantly blows away the soil, 90 meteorites were found. Hundreds of meteorites have been discovered on the surface of evaporating glaciers in Antarctica. Recently fallen meteorites are covered with a vitrified, sintered crust that is darker than the interior. Meteorites are of great scientific interest; Most major natural science museums and many universities have meteorite experts.

METEORITE, possibly coming from Mars. Discovered in Antarctica in 1984.

Types of meteorites. There are meteorites made of various substances. Some are primarily composed of an iron-nickel alloy containing up to 40% nickel. Among fallen meteorites only 5.7% are iron, but in collections their share is much larger, since they deteriorate more slowly under the influence of water and wind, and they are also easier to detect by appearance. If you polish a section of an iron meteorite and lightly etch it with acid, you can often see a crystalline pattern of intersecting stripes formed by alloys with different nickel contents. This drawing is called “Widmanstätten figures” in honor of A. Widmanstätten (1754–1849), who was the first to observe them in 1808.

The IRON METEORITE from Henbury (Australia) is a typical metallic type meteorite, many of which are rich in compounds found in iron ores.

Stony meteorites are divided into two large groups: chondrites and achondrites. Chondrites are the most common, accounting for 84.8% of all fallen meteorites. They contain rounded millimeter-sized grains - chondrules; Some meteorites are composed almost entirely of chondrules. Chondrules have not been found in terrestrial rocks, but glassy grains of similar size have been found in lunar soil. Chemists have studied them carefully because the chemical composition of chondrules likely represents the primordial matter of the solar system. This standard composition is called the “cosmic abundance of elements.” In chondrites of a certain type, containing up to 3% carbon and 20% water, signs of biological matter were intensively searched, but no signs of living organisms were found in either these or other meteorites. Achondrites lack chondrules and resemble lunar rock in appearance.

METEORITE-ACHONDRITE

METEORITE-CHONDRITE

Parent bodies of meteorites. The study of the mineralogical, chemical and isotopic composition of meteorites has shown that they are fragments of larger objects in the Solar System. The maximum radius of these parent bodies is estimated at 200 km. Most are approximately the same size large asteroids. The estimate is based on the cooling rate of the iron meteorite, at which two alloys with nickel are obtained, forming Widmanstätten figures. Rocky meteorites were likely dislodged from the surface of small, atmosphereless, cratered planets like the Moon. Cosmic radiation destroyed the surface of these meteorites in the same way as moon rocks. However, the chemical composition of meteorites and lunar samples is so different that it is quite obvious that the meteorites did not come from the Moon. Scientists were able to photograph two meteorites as they fell and calculate their orbits from the photographs: it turned out that these bodies came from the asteroid belt. Asteroids are likely the main sources of meteorites, although some may be particles from evaporated comets.

METEOR. The word "meteor" in Greek was used to describe various atmospheric phenomena, but now it refers to phenomena that occur when particulate matter from space enters the upper atmosphere. In the narrow sense, a “meteor” is a luminous streak along the path of a decaying particle. However, in everyday life this word often refers to the particle itself, although scientifically it is called a meteoroid. If part of a meteoroid reaches the surface, it is called a meteorite. Meteors are popularly called “shooting stars.” Very bright meteors are called fireballs; Sometimes this term refers only to meteor events accompanied by sound phenomena.

Frequency of occurrence. The number of meteors that an observer can see in a given period of time is not constant. In good conditions, away from city lights and in the absence of bright moonlight, an observer may notice 5–10 meteors per hour. Most meteors glow for about a second and appear fainter than the brightest stars. After midnight, meteors appear more often, since the observer at this time is located on the forward side of the Earth along the orbital movement, which receives more particles. Each observer can see meteors within a radius of about 500 km around themselves. In total, hundreds of millions of meteors appear in the Earth’s atmosphere every day. The total mass of particles entering the atmosphere is estimated at thousands of tons per day - an insignificant amount compared to the mass of the Earth itself. Measurements from spacecraft show that about 100 tons of dust particles, too small to cause the appearance of visible meteors, also hit the Earth per day.

Meteor observation. Visual observations provide a lot of statistical data about meteors, but special instruments are needed to accurately determine their brightness, altitude and flight speed. Astronomers have been using cameras to photograph meteor trails for about a century. A rotating shutter in front of the camera lens makes the meteor trail look like a dotted line, which helps accurately determine time intervals. Typically, this shutter is used to make 5 to 60 exposures per second. If two observers, separated by a distance of tens of kilometers, simultaneously photograph the same meteor, then it is possible to accurately determine the particle's flight altitude, the length of its trail and, based on time intervals, the flight speed.

Since the 1940s, astronomers have observed meteors using radar. The cosmic particles themselves are too small to be detected, but as they fly through the atmosphere they leave a plasma trail that reflects radio waves. Unlike photography, radar is effective not only at night, but also during the day and in cloudy weather. The radar detects small meteoroids that are inaccessible to the camera. Photographs help determine the flight path more accurately, and radar allows you to accurately measure distance and speed.

Television equipment is also used to observe meteors. Electron-optical converters make it possible to register faint meteors. Cameras with CCD matrices are also used. In 1992, while recording a sports competition on a video camera, the flight of a bright fireball was recorded, ending with the fall of a meteorite.

Speed and altitude. The speed at which meteoroids enter the atmosphere ranges from 11 to 72 km/s. The first value is the speed acquired by the body only due to the gravity of the Earth. (A spacecraft must achieve the same speed in order to escape from the Earth’s gravitational field.) A meteoroid arriving from distant regions of the Solar System, due to attraction to the Sun, acquires a speed of 42 km/s near the Earth’s orbit. The Earth's orbital speed is about 30 km/s. If the meeting occurs head-on, then their relative speed is 72 km/s. Any particle arriving from interstellar space must have an even greater speed. The absence of such fast particles proves that all meteoroids are members of the Solar System.

BRIGHT METEOR from the Perseid shower.

The altitude at which a meteor begins to glow or is detected by radar depends on the particle's entry speed. For fast meteoroids, this height can exceed 110 km, and the particle is completely destroyed at an altitude of about 80 km. In slow-moving meteoroids, this occurs lower down, where the air density is greater. Meteors, comparable in brilliance to the brightest stars, are formed by particles with a mass of tenths of a gram. Larger meteoroids usually take longer to break up and reach lower altitudes. They are significantly slowed down due to friction in the atmosphere. Rare particles fall below 40 km. If a meteoroid reaches altitudes of 10–30 km, then its speed becomes less than 5 km/s and it may fall to the surface as a meteorite.

Orbits. Knowing the meteoroid's speed and the direction from which it approached Earth, an astronomer can calculate its orbit before impact. The Earth and the meteoroid collide when their orbits intersect and they simultaneously find themselves at this intersection point. The orbits of meteoroids can be either almost circular or extremely elliptical, extending beyond planetary orbits.

If a meteoroid approaches the Earth slowly, it means it is moving around the Sun in the same direction as the Earth: counterclockwise, as seen from the north pole of the orbit. Most meteoroid orbits extend beyond the Earth's orbit, and their planes are not very inclined to the ecliptic. The fall of almost all meteorites is associated with meteoroids that had speeds of less than 25 km/s; their orbits lie entirely within the orbit of Jupiter. These objects spend most of their time between the orbits of Jupiter and Mars, in the belt of minor planets - asteroids. Therefore, it is believed that asteroids serve as a source of meteorites. Unfortunately, we can only observe meteoroids that cross the Earth's orbit; Obviously, this group does not fully represent all the small bodies of the Solar System.

Fast meteoroids have more elongated orbits and are more inclined to the ecliptic. If a meteoroid approaches at a speed of more than 42 km/s, then it moves around the Sun in the direction opposite to the direction of the planets. The fact that many comets move in such orbits indicates that these meteoroids are fragments of comets.

Meteor showers. On some days of the year, meteors appear much more often than usual. This phenomenon is called a meteor shower, where tens of thousands of meteors are observed per hour, creating an amazing "star shower" phenomenon across the entire sky. If you trace the paths of meteors in the sky, it will seem that they all fly out from one point, called the radiant of the shower. This phenomenon of perspective, like rails converging at the horizon, indicates that all particles are moving along parallel trajectories.

Astronomers have identified several dozen meteor showers, many of which show annual activity lasting from a few hours to several weeks. Most showers are named after the constellation in which their radiant lies, for example, the Perseids, which have a radiant in the constellation Perseus, and the Geminids, which have a radiant in Gemini.

Meteor showers are observed when the Earth crosses the path of a swarm of particles formed by the destruction of a comet. Approaching the Sun, the comet is heated by its rays and loses matter. Over several centuries, under the influence of gravitational disturbances from the planets, these particles form an elongated swarm along the comet’s orbit. If the Earth crosses this stream, we can observe a shower of stars every year, even if the comet itself is far from Earth at that moment. Because the particles are not evenly distributed along the orbit, the intensity of rain may vary from year to year. The old flows are so expanded that the Earth crosses them for several days. In cross-section, some threads resemble a ribbon rather than a cord.

The ability to observe the flow depends on the direction of arrival of particles to the Earth. If the radiant is located high in the northern sky, then the stream is not visible from the southern hemisphere of the Earth (and vice versa). The shower's meteors can only be seen if the radiant is above the horizon. If the radiant hits the daytime sky, then the meteors are not visible, but they can be detected by radar. Narrow streams under the influence of planets, especially Jupiter, can change their orbits. If they no longer cross the Earth's orbit, they become unobservable.

The December Geminid shower is associated with the remnants of a minor planet or the inactive nucleus of an old comet. There are indications that the Earth collides with other groups of meteoroids generated by asteroids, but these streams are very weak.

Fireballs. Meteors that are brighter than the brightest planets are often called fireballs. Sometimes fireballs are observed brighter than the full moon and extremely rarely those that flare brighter than the sun. Fireballs arise from the largest meteoroids. Among them are many fragments of asteroids, which are denser and stronger than fragments of cometary nuclei. But still, most asteroid meteoroids are destroyed in dense layers of the atmosphere. Some of them fall to the surface as meteorites. Due to the high brightness of the flares, fireballs appear much closer than they really are. Therefore, it is necessary to compare observations of fireballs from different places before organizing a search for meteorites. Astronomers estimate that every day around the Earth, about 12 fireballs end in the fall of meteorites of more than a kilogram.

Physical processes. The destruction of a meteoroid in the atmosphere occurs by ablation, i.e. high-temperature detachment of atoms from its surface under the influence of incident air particles. The hot gas trail remaining behind the meteoroid emits light, but not as a result of chemical reactions, but as a result of the recombination of atoms excited by the impacts. In the spectra of meteors, many bright emission lines are visible, among which the lines of iron, sodium, calcium, magnesium and silicon predominate. Atmospheric nitrogen and oxygen lines are also visible. The chemical composition of meteoroids determined from the spectrum is consistent with data on comets and asteroids, as well as on interplanetary dust collected in upper layers atmosphere.

Many meteors, especially fast ones, leave behind a luminous trail that is visible for a second or two, and sometimes for much longer. When large meteorites fell, the trail was observed for several minutes. The glow of oxygen atoms at altitudes of approx. 100 km can be explained by tracks lasting no more than a second. Longer trails arise from the complex interaction of the meteoroid with the atoms and molecules of the atmosphere. Dust particles along the bolide's trajectory can form a bright trail if the upper layers of the atmosphere, where they are scattered, are illuminated by the Sun, when the observer below is in deep twilight.

The speeds of meteoroids are hypersonic. When a meteoroid reaches relatively dense layers of the atmosphere, a powerful shock wave occurs, and strong sounds can be carried tens of kilometers or more. These sounds are reminiscent of thunder or distant cannonade. Due to the great distance, the sound arrives a minute or two after the car appears. For several decades, astronomers have debated the reality of the anomalous sound, which some observers heard directly at the moment the fireball appeared and described it as a crackling or whistling sound. Research has shown that the sound is caused by disturbances in the electric field near the car, under the influence of which objects close to the observer - hair, fur, trees - produce sound.

Meteorite danger. Large meteoroids can destroy spacecraft, and small dust particles constantly wear away their surface. The impact of even a small meteoroid can impart an electrical charge to a satellite, which will disable electronic systems. The risk is generally low, but spacecraft launches are still sometimes postponed if a strong meteor shower is expected.

Bibliography

1 Simonenko A.N. Meteorites are fragments of asteroids. M., 1979

2 Getman V.S. Grandchildren of the Sun. M., 1989

Minor planets – asteroids (Greek asteroedeis - star-like) have nothing in common with stars, and are named so only because they are visible through a telescope as point objects. The history of the discovery of small planets is interesting. By the end of the 18th century. the empirical law of planetary distances was known (the so-called Titius-Bode rule), according to which there should have been another unknown planet between Mars and Jupiter. The search for it led the astronomer Piazzi to the discovery in 1801 of the planet Ceres with a diameter of 1003 km. The discovery of three more planets: Pallas - 608 km, Juno - 180 km and Vesta - 538 km - was unexpected. In recent years, asteroids up to 1 km in diameter have been discovered, and their total number reaches several thousand. Since asteroids move, during long photographic exposures they appear as bright white lines against a black background of the starry sky.

The total mass of all asteroids is estimated at 0.01 Earth masses. Their common attraction does not cause noticeable disturbances in the movement of Mars and other planets.

Currently, astronomers are concerned about the unusual “invasion” of large celestial bodies in the vicinity of the planets of the solar system. Thus, in May 1996, two asteroids flew at a short distance from the Earth. Many experts suggest that the solar system fell into a kind of trail of large celestial bodies formed outside our system, and therefore believe that, along with the nuclear threat, the number one danger for our planet has become the danger posed by asteroids. A new important problem has arisen - the creation of space protection of the Earth from asteroids, which should include both ground-based and space-based assets, including those located in deep space. The creation of such a system should be carried out on an international basis.

On the other hand, the increase in the number of visible asteroids can be explained by the increase in the volume of astronomical information in recent years, after observations were transferred from the Earth's surface to near space.

Comets (Greek cometes - long-haired) - small bodies of the Solar System, moving in highly elongated elliptical or even parabolic orbits. Some comets have perihelia near the Sun and aphelion outside Pluto. The movement of comets in orbits can be either forward or backward. The planes of their orbits lie in different directions from the Sun. The orbital periods of comets vary greatly: from several years to many thousands of years. A tenth of the known comets (about 40) have appeared more than once; they are called periodic.

Comets have a head and a tail. The head consists of a hard core and coma. The core is an ice conglomerate of frozen gases (water vapor, carbon dioxide, methane, ammonia, etc.) with an admixture of refractory silicates, carbon dioxide and metal particles - iron, manganese, nickel, sodium, magnesium, calcium, etc. It is assumed that the core contains organic molecules. Comet nuclei are small, their diameter ranges from several hundred meters to several (50 – 70) kilometers. Coma is a gas-dust environment (hydrogen, oxygen, etc.), glowing when approaching the Sun. Near perihelion, from the comet’s nucleus, under the influence of solar heat and corpuscular flows, “evaporation” (sublimation) of frozen gases occurs and a luminous tail of the comet is formed, sometimes more than one. It consists of rarefied gases and small solid particles and is directed in the direction opposite to the Sun. The length of the tails reaches hundreds of millions of kilometers. The Earth has fallen into the tails of comets more than once, for example in 1910. This then caused great concern among people, although falling into comet tails does not pose any danger to the Earth: they are so rarefied that the admixture of poisonous gases contained in the composition comet tails(methane, cyanogen), imperceptible in the atmosphere.

Among periodic comets, the most interesting is Halley's comet, named after the English astronomer who discovered it in 1682 and calculated its orbital period (about 76 years). It was in its tail that the Earth found itself in 1910. It last appeared in the sky in April 1986, passing at a distance of 62 million km from Earth. Careful studies of the comet using spacecraft showed that the icy core of the comet is a monolithic body of irregular shape measuring about 15x7 km, around which a giant hydrogen corona with a diameter of 10 million km was discovered.

Comets are short-lived celestial bodies, since as they approach the Sun they gradually “melt” due to the intense outflow of gases or break up into a swarm of meteors. The meteoric material is subsequently more or less evenly distributed throughout the entire orbit of the parent comet. In this regard, the history of the periodic (about 7 years) comet Bijela, discovered in 1826, is interesting. Twice after its discovery, astronomers observed its appearance, and the third time, in 1846, they managed to record its division into two parts, which, on subsequent returns They were moving further and further away from each other. Then the meteoric substance of the comet stretched across the entire orbit, during which the Earth crossed an abundant “rain” of meteors.

There is no precise evidence that the Earth has ever collided with a comet nucleus. No more than five comets penetrate into Earth's orbit each year. However, there is a version that the famous Tunguska “meteorite”, which fell in 1908 in the basin of the Podkamennaya Tunguska River, near the village of Vanavara, is a small (about 30 m) fragment of the nucleus of comet Encke, which exploded as a result of thermal heating in the atmosphere, and the “ice” " and solid impurities "evaporated". At the same time, the explosive air wave felled a forest over an area within a radius of 30 km.

In 1994, scientists observed the fall of Comet Shoemaker-Levy onto Jupiter. At the same time, it broke up into dozens of fragments 3–4 km in diameter, which flew one after another at an enormous speed - about 70 km/s, exploded in the atmosphere and evaporated. The explosions created a gigantic hot cloud 20 thousand km in size and with a temperature of 30,000 °C. The fall of such a comet to Earth would end in a cosmic catastrophe.

It is believed that the “comet cloud” surrounding the Sun formed along with the Solar System. Therefore, by studying the material of comets, scientists obtain information about the primary material from which planets and satellites were formed. In addition, assumptions have emerged about the “participation” of comets in the origin of life on Earth, since radio spectroscopic methods have proven the presence of complex organic compounds (formaldehyde, cyanoacetylene, etc.) in comets and meteorites.

Meteors, usually called “shooting stars”, are tiny (mg) solid particles that fly into the atmosphere at speeds of up to 50 - 60 km/s, heat up due to friction with the air to several thousand degrees Celsius, ionize gas molecules, causing them to emit light, and evaporate at an altitude of 80–100 km above the earth’s surface. Sometimes a large and exceptionally bright fireball appears in the sky, which can break apart and even explode during flight. Such a meteor is called fireball. A similar fireball exploded on September 25, 2002 in the Irkutsk region, between the villages of Mama and Bodaibo. In the sky, both individual meteors appearing randomly in the sky, and groups of meteors in the form of meteor showers, within which particles move parallel to each other, although in perspective it seems that they are scattering from one point in the sky, called radiant. Meteor showers are named by the constellations in which their radiants are located. The Earth crosses the orbit of the Perseids around August 12, the Orionids - October 20, the Leonids - November 18, etc. Meteor showers move along the orbits of those asteroids or comets, as a result of the disintegration of which they are formed. The orbits of meteor showers are carefully studied for the safety of spacecraft and vehicles.

Meteorites(from Greek meteora - celestial phenomena) are large meteoroids that fall to Earth. Every year, about two thousand meteorites with a total mass of about 20 tons fall onto the earth's surface. They are fragments of a rounded angular shape, usually covered with a thin black melting crust with numerous cells from the drilling action of air jets. According to their structure, they are of three classes: iron, consisting mainly of nickel iron, stone, which contain predominantly silicate minerals, and iron-stone, consisting of a mixture of these substances. Among the stony ones, there are two groups: chondrites (granular meteorites) and achondrites (earthy meteorites). Stony meteorites predominate (Fig. 3). Physico-chemical analysis of meteorites indicates that they consist of chemical elements and their isotopes known on Earth, which confirms the unity of matter in the Universe.

Rice. 3. a – relative frequency of meteorite falls of different classes (according to J. Boud); b – mineral composition of a typical chondrite (according to V. E. Khain)

The largest Goba meteorite, measuring 2.75x2.43 m and weighing 59 tons, was found in southwest Africa; it is iron. The Sikhote-Alin meteorite (fell in 1947) split into thousands of pieces in the air and fell to Earth as “iron rain.” The total weight of the collected fragments is about 23 tons; they created 24 impact craters ranging from 8 to 26 m in diameter. The Kaaba meteorite (“Black Stone”) is kept in the Mecca mosque in Saudi Arabia and serves as an object of worship for Muslims. Many meteorites have been discovered in Antarctica, and they are also found in the sediments of the floor of the World Ocean.

At the dawn of the Earth's existence, when there was still a lot of unused material in the solar system, and the Earth's atmosphere - protection from meteorites - was still very thin, the number of meteorites bombarding the Earth was enormous and its surface resembled the face of the Moon. Over time, most of the craters were destroyed by tectonic and exogenous processes, but many of them were still preserved in the form of ring-shaped geological structures called astroblemes(“star scars”). They are especially visible from space. They reach tens of kilometers in diameter. The study of meteorites allows us to judge the structure and properties of celestial bodies and supplements our information about the internal structure of the Earth.

Minor planets - asteroids (Greek asteroedeis- star-like) have nothing in common with stars, and are named so only because they are visible through a telescope as point objects. The history of the discovery of small planets is interesting. By the end of the 18th century. the empirical law of planetary distances was known (the so-called Titius-Bode rule), according to which there should have been another unknown planet between Mars and Jupiter. The search for it led the astronomer Piazzi to the discovery in 1801 of the planet Ceres with a diameter of 1003 km. The discovery of three more planets: Pallas - 608 km, Juno - 180 km and Vesta - 538 km - was unexpected. In recent years, asteroids up to 1 km in diameter have been discovered, and their total number reaches several thousand. Since asteroids move, during long photographic exposures they appear as bright white lines against a black background of the starry sky.

The total mass of all asteroids is estimated at 0.01 Earth masses. Their common attraction does not cause noticeable disturbances in the movement of Mars and other planets.

Currently, astronomers are concerned about the unusual “invasion” of large celestial bodies in the vicinity of the planets of the solar system. Thus, in May 1996, two asteroids flew at a short distance from the Earth. Many experts suggest that the solar system fell into a kind of trail of large celestial bodies formed outside our system, and therefore believe that, along with the nuclear threat, the number one danger for our planet has become the danger posed by asteroids. A new important problem has arisen - the creation of space protection of the Earth from asteroids, which should include both ground-based and space-based assets, including those located in deep space. The creation of such a system should be carried out on an international basis.

Comets(Greek cometes- long-haired) - small bodies of the Solar System, moving in highly elongated elliptical or even parabolic orbits. Some comets have perihelia near the Sun and aphelion outside Pluto. The movement of comets in orbits can be either forward or backward. The planes of their orbits lie in different directions from the Sun. The orbital periods of comets vary greatly: from several years to many thousands of years. A tenth of the known comets (about 40) have appeared more than once; they are called periodic.

Comets have a head and a tail. The head consists of a hard core and coma. The core is an ice conglomerate of frozen gases (water vapor, carbon dioxide, methane, ammonia, etc.) with an admixture of refractory silicates, carbon dioxide and metal particles - iron, manganese, nickel, sodium, magnesium, calcium, etc. It is assumed that the core contains organic molecules. Comet nuclei are small, their diameter ranges from several hundred meters to several (50 – 70) kilometers. Coma is a gas-dust environment (hydrogen, oxygen, etc.), glowing when approaching the Sun. Near perihelion, from the comet’s nucleus, under the influence of solar heat and corpuscular flows, “evaporation” (sublimation) of frozen gases occurs and a luminous tail of the comet is formed, sometimes more than one. It consists of rarefied gases and small solid particles and is directed in the direction opposite to the Sun. The length of the tails reaches hundreds of millions of kilometers. The Earth has fallen into the tails of comets more than once, for example in 1910. This then caused great concern among people, although falling into comet tails does not pose any danger to the Earth: they are so rarefied that the admixture of poisonous gases contained in comet tails (methane, cyan), is imperceptible in the atmosphere.

Among periodic comets, the most interesting is Halley's comet, named after the English astronomer who discovered it in 1682 and calculated its orbital period (about 76 years). It was in its tail that the Earth found itself in 1910. It last appeared in the sky in April 1986, passing at a distance of 62 million km from Earth. Careful studies of the comet using spacecraft showed that the icy core of the comet is a monolithic body of irregular shape measuring about 15x7 km, around which a giant hydrogen corona with a diameter of 10 million km was discovered.

Comets are short-lived celestial bodies, since as they approach the Sun they gradually “melt” due to the intense outflow of gases or break up into a swarm of meteors. The meteoric material is subsequently more or less evenly distributed throughout the entire orbit of the parent comet. In this regard, the history of the periodic (about 7 years) comet Bijela, discovered in 1826, is interesting. Twice after its discovery, astronomers observed its appearance, and the third time, in 1846, they managed to record its division into two parts, which, on subsequent returns They were moving further and further away from each other. Then the meteoric substance of the comet stretched across the entire orbit, during which the Earth crossed an abundant “rain” of meteors.

There is no precise evidence that the Earth has ever collided with a comet nucleus. No more than five comets penetrate into Earth's orbit each year. However, there is a version that the famous Tunguska “meteorite”, which fell in 1908 in the river basin Podkamennaya Tunguska, near the village of Vanavara, is a small (about 30 m) fragment of the nucleus of comet Encke, which, as a result of thermal heating in the atmosphere, exploded, and the “ice” and solid impurities “evaporated”. At the same time, the explosive air wave felled a forest over an area within a radius of 30 km.

It is believed that the “comet cloud” surrounding the Sun formed along with the Solar System. Therefore, by studying the material of comets, scientists obtain information about the primary material from which planets and satellites were formed. In addition, assumptions have emerged about the “participation” of comets in the origin of life on Earth, since radio spectroscopic methods have proven the presence of complex organic compounds (formaldehyde, cyanoacetylene, etc.) in comets and meteorites.

Meteors, usually called “shooting stars”, are tiny (mg) solid particles that fly into the atmosphere at speeds of up to 50 - 60 km/s, heat up due to friction with the air to several thousand degrees Celsius, ionize gas molecules, causing them to emit light, and evaporate at an altitude of 80–100 km above the earth’s surface. Sometimes a large and exceptionally bright fireball appears in the sky, which can break apart and even explode during flight. Such a meteor is called fireball. A similar fireball exploded on September 25, 2002 in the Irkutsk region, between the villages of Mama and Bodaibo. In the sky, both individual meteors appearing randomly in the sky, and groups of meteors in the form of meteor showers, within which particles move parallel to each other, although in perspective it seems that they are scattering from one point in the sky, called radiant. Meteor showers are named by the constellations in which their radiants are located. The Earth crosses the orbit of the Perseids around August 12, the Orionids - October 20, the Leonids - November 18, etc. Meteor showers move along the orbits of those asteroids or comets, as a result of the disintegration of which they are formed. The orbits of meteor showers are carefully studied for the safety of spacecraft and vehicles.

Meteorites(from Greek meteora- celestial phenomena) are large meteoroids that fall to Earth. Every year, about two thousand meteorites with a total mass of about 20 tons fall onto the earth's surface. They are fragments of a rounded angular shape, usually covered with a thin black melting crust with numerous cells from the drilling action of air jets. According to their structure, they are of three classes: iron, consisting mainly of nickel iron, stone, which contain predominantly silicate minerals, and iron-stone, consisting of a mixture of these substances. Among the stony ones, there are two groups: chondrites (granular meteorites) and achondrites (earthy meteorites). Stony meteorites predominate (Fig. 3). Physico-chemical analysis of meteorites indicates that they consist of chemical elements and their isotopes known on Earth, which confirms the unity of matter in the Universe.

Rice. 3. a – relative frequency of meteorite falls of different classes (according to J. Boud); b – mineral composition of a typical chondrite (according to V. E. Khain)

The largest Goba meteorite, measuring 2.75x2.43 m and weighing 59 tons, was found in southwest Africa; it is iron. The Sikhote-Alin meteorite (fell in 1947) split into thousands of pieces in the air and fell to Earth as “iron rain.” The total weight of the collected fragments is about 23 tons; they created 24 impact craters ranging from 8 to 26 m in diameter. The Kaaba meteorite (“Black Stone”) is kept in the Mecca mosque in Saudi Arabia and serves as an object of worship for Muslims. Many meteorites have been discovered in Antarctica, and they are also found in the sediments of the floor of the World Ocean.

At the dawn of the Earth's existence, when there was still a lot of unused material in the solar system, and the Earth's atmosphere - protection from meteorites - was still very thin, the number of meteorites bombarding the Earth was enormous and its surface resembled the face of the Moon. Over time, most of the craters were destroyed by tectonic and exogenous processes, but many of them were still preserved in the form of ring-shaped geological structures called astroblemes(“star scars”). They are especially visible from space. They reach tens of kilometers in diameter. The study of meteorites allows us to judge the structure and properties of celestial bodies and supplements our information about the internal structure of the Earth.

Moon

The Earth is often, and not without reason, called the double planet Earth-Moon. The Moon (Selene, goddess of the Moon in Greek mythology), our celestial neighbor, was the first to be directly studied.

General information about the Moon. Movements of the Moon. The Moon is a natural satellite of the Earth, located at a distance of 384 thousand km (60 radii of the Earth). The average radius of the Moon is 1738 km (almost 4 times less than the Earth's). The Moon's mass is 1/81 that of the Earth, which is significantly greater than similar ratios for other planets in the Solar System (except for the Pluto-Charon pair); therefore, the Earth–Moon system is considered a double planet. It has a common center of gravity - the so-called barycenter, which is located in the body of the Earth at a distance of 0.73 radii from its center (1700 km from the surface of the Ocean). Both components of the system rotate around this center, and it is the barycenter that moves in orbit around the Sun. The average density of lunar substance is 3.3 g/cm3 (terrestrial - 5.5 g/cm3). The volume of the Moon is 50 times smaller than the Earth. The force of lunar gravity is 6 times weaker than the earth's. The moon rotates around its axis, which is why it is slightly flattened at the poles. The axis of rotation of the Moon makes an angle of 83°22" with the plane of the lunar orbit. The plane of the Moon's orbit does not coincide with the plane of the Earth's orbit and is inclined to it at an angle of 5°9". The intersection of the orbits of the Earth and the Moon is called nodes of the lunar orbit.

The orbit of the Moon is an ellipse, in one of the foci of which the Earth is located, therefore the distance from the Moon to the Earth varies from 356 to 406 thousand km. The period of orbital revolution of the Moon and, accordingly, the same position of the Moon on the celestial sphere is called sidereal(sidereal) month (lat. sidus, sideris(genus) – star). It is 27.3 Earth days. The sidereal month coincides with the period of the daily rotation of the Moon around its axis due to their identical angular speed (= 13.2° per day), established due to the braking effect of the Earth. Due to the synchronicity of these movements, the Moon always faces us with one side. However, we see almost 60% of its surface thanks to libration– the apparent rocking of the Moon up and down (due to the mismatch of the planes of the lunar and earth’s orbits and the inclination of the Moon’s rotation axis to the orbit) and left and right (due to the fact that the Earth is in one of the foci of the lunar orbit, and the visible hemisphere of the Moon looks at the center of the ellipse ).

When moving around the Earth, the Moon takes different positions relative to the Sun. Associated with this are various Moon phases, i.e., different forms of its visible part. Main four phases: new moon, first quarter, full moon, last quarter. The line on the surface of the Moon separating the illuminated part of the Moon from the unlit part is called terminator(Fig. 4).

During the new moon, the Moon is between the Sun and the Earth and faces the Earth with its unlit side, therefore invisible. In the first quarter, the Moon is visible from the Earth at an angular distance of 90° from the Sun, and the sun's rays illuminate only the right half of the side of the Moon facing the Earth. During a full moon, the Earth is between the Sun and the Moon, the hemisphere of the Moon facing the Earth is brightly illuminated by the Sun, and the Moon is visible as a full disk. During the last quarter, the Moon is again visible from the Earth at an angular distance of 90° from the Sun, and the sun's rays illuminate the left half of the visible side of the Moon. In the intervals between these main phases, the Moon is visible either as a crescent or as an incomplete disk.

The period of complete change of lunar phases, i.e. the period of the Moon returning to its original position relative to the Sun and Earth, is called synodic month. It averages 29.5 mean solar days. During the synodic month on the Moon there is a change of day and night once, the duration of which is 14.7 days. The synodic month is more than two days longer than the sidereal month. This is the result of the fact that the direction of the axial rotation of the Earth and the Moon coincides with the direction of the orbital motion of the Moon. When the Moon completes a full revolution around the Earth in 27.3 days, the Earth will advance approximately 27° in its orbit around the Sun, since its angular orbital speed is about 1° per day. In this case, the Moon will take the same position among the stars, but will not be in the full moon phase, since for this it needs to advance in its orbit another 27° behind the “escaped” Earth. Since the angular velocity of the Moon is approximately 13.2° per day, it covers this distance in about two days and additionally moves another 2° behind the moving Earth. As a result, the synodic month turns out to be more than two days longer than the sidereal month (Fig. 5). Although the Moon moves around the Earth from west to east, its apparent movement in the sky occurs from east to west due to high speed rotation of the Earth compared to the orbital motion of the Moon. Moreover, during the upper climax ( highest point its path in the sky) The moon shows the direction of the meridian (north - south), which can be used for approximate orientation on the ground. And since the upper culmination of the Moon at different phases occurs at different hours of the day: during the first quarter - about 18 o'clock, during the full moon - at midnight, during the last quarter - about 6 o'clock in the morning (local time), this can also be used for rough estimate of time at night.

Physical nature of the Moon. Intensive study of the physical nature of the Moon began in 1959, when the Soviet spacecraft Luna 2 first reached the surface of the Moon, and Luna 3 photographed the far side of the Moon from space. In 1966, Luna-9 made a soft landing on the Moon, establishing that the planet's soil had a solid structure, and not dusty, as some scientists believed. On July 21, 1969, earthlings visited the Moon for the first time - Americans Neil Armstrong and Edwin Aldrin. In 1970 and 1973 Soviet automatic mobile devices - lunar rovers - operated on the Moon for several months. They transmitted more than 20,000 images to Earth and studied the chemical composition and physical and mechanical properties of the lunar soil.

Currently, the relief of the Moon is quite well studied. The dark areas visible to the naked eye, once called “seas,” turned out to be vast waterless lowland plains (the largest is the “Ocean of Storms”), and the light areas—the “continents”—are represented by elevated and mountainous spaces. The maximum height amplitude is more than 10 km. The main planetary structures of the lunar surface are ring craters with a diameter of up to 20–30 km and multi-ring cirques with a diameter of 200 to 1000 km, bordered by mountainous areas. It is assumed that the ring structures have different origins - meteorite, volcanic or combined shock-explosive. A specialist in the relief of planetary bodies, A. A. Lukashov, believes that the structure of the surface of the Moon “demonstrates the subordinate role of endogenous factors compared to cosmogenic factors...”. The meteorite theory is currently the most accepted. Linear formations are also common on the Moon: tectonic faults, elongated mountain ranges and ridges (Caucasus, Alps, Apennines, Carpathians, etc.).

Studies of lunar soil samples delivered to Earth in 1970–1973. American astronauts on the Apollo spacecraft and Soviet spacecraft“Luna” showed that in terms of mineralogical and petrographic composition, the surface clastic rocks of the Moon (the so-called regolith) are similar to terrestrial igneous rocks - basalts, etc. The thickness of the lunar crust is about 65 km. In the crust of the “seas” there is an increased content of heavy elements (iron, titanium, chromium, zirconium, thorium, etc.), in the crust of the “continents” - oxides of silicon, aluminum, sodium, potassium. The lunar surface albedo averages about 7%. The lunar soil, saturated with inert gases, has extremely low thermal conductivity, which is why at a depth of 0.5 m there is a constant temperature of about –50 °C. The Moon's magnetic field is very weak.

The Moon has neither an atmosphere nor a hydrosphere. The temperature on the surface of the Moon varies from +130°C on the illuminated side to –170°C on the shadow side. The reason for temperature contrasts is the lack of air. And since there is no air, there is no wind, no sounds, no clouds, no rain, there is no dawn, no twilight, no rainbow. The sky there is always completely black, on it you can simultaneously see the stars, the Sun and the Earth, which hangs in the sky in the same place.

The main factors in the destruction of rocks on the surface of the Moon and changes in its face are: 1) daily temperature fluctuations; 2) bombardment by meteorites, leading to the melting and sintering of surface rocks and reducing the gravitational displacement of the material; 3) irradiation of surface rocks by solar wind; 4) space vacuum, which must be taken into account during the outpouring of magma onto the surface and its intensive splashing in the early geological epochs(about 2 billion years ago). Now the deep activity of the Moon is weakened, and it is a tectonically lifeless body; moonquakes are rare. The lunar landscape is a rocky desert. With such natural conditions Organic life on the Moon is impossible. There is no generally accepted point of view on the formation of the Moon (“is it a daughter or a “sister” of the Earth?).

Ebbs and flows on Earth. The Moon, being closest to the Earth and largest in mass cosmic body, has the greatest gravitational effect on it, causing tides And low tides in all shells of the Earth: lithosphere, atmosphere, hydrosphere and biosphere. Tidal force– the resultant of the gravitational force of the Moon and the centrifugal force that arises during the rotation of the Earth-Moon system around the barycenter. On Earth, there are simultaneously two high tides at the closest point to the Moon and the most distant one, and two low tides at points located at an angular distance of 90° from the Moon-Earth line (Fig. 6). Since the Moon revolves around the Earth from west to east and travels 13.2° in its orbit during a solar day (24 hours), then lunar day- the period of time between two successive climaxes of the Moon on any meridian of the Earth - turns out to be longer than the solar day by 50 minutes and equal to 24 hours 50 minutes. During the lunar day there are two high tides and two low tides on Earth. The full tidal cycle, i.e. the change in water level in the World Ocean, where the ebb and flow of the tides are most pronounced, between successive high tides (or low tides), is completed in 12 hours 25 minutes, and 6 hours 12 minutes 30 seconds pass between high tide and low tide.

– gravitational force

- centrifugal force

– resultant force

Rice. 6. Tidal forces of the Moon (according to L.K. Davydov and others)

Simultaneously with lunar tides, there are also solar tides with a full period of 24 hours, but they are 2.2 times weaker than lunar tides due to the great distance of the Sun from the Earth. Lunar and solar tides add up to new and full moons (syzygy tides) and are deducted in the first and last quarter (quadrature tides). The former are approximately 40% higher than the latter.

The general planetary significance of tidal waves is that, moving from east to west following the apparent movement of the Moon, they slow down the axial rotation of the Earth and lengthen the day (by 0.0016 With per century). At the same time, not only the figure of the Earth changes due to the slow decrease in polar compression, but also the face of the Earth. Thanks to the tides, all the shells of the Earth continuously pulsate. They cause daily vertical displacements earth's surface up to 50 cm, semi-diurnal fluctuations in surface atmospheric pressure, change the conditions of organic life in the coastal parts of the World Ocean, form the shores, i.e. participate in many natural processes, and also influence economic activity coastal countries.

Rice. 7. Solar (a – total, b – partial) and lunar (total) eclipses

Lunar and solar eclipses. Occur periodically on Earth lunar And solar eclipses. They are observed when the Sun, Earth and Moon are on the same line, that is, when the new moon or full moon occurs near the nodes of the lunar orbit. During the new moon phase, the Moon blocks the disk of the Sun with its opaque body for residents of some regions of the Earth - this happens solar eclipse(full, partial, ring-shaped). During the full moon phase, being on the same line with the Sun and the Earth, the Moon falls into the cone-shaped shadow of the Earth - a lunar eclipse occurs (total or partial), visible on the night hemisphere of the Earth (Fig. 7).

Planets meteorites comets. The most common point of view is that planets are fragments of small planets. A meteorite is a solid body of cosmic origin that fell to the surface of the Earth. Most meteorites found weigh between

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