What are asteroids comets meteors meteorites. What is a meteor? Meteora: photo

The largest collection of amazing information about celestial bodies. Interesting facts about comets and asteroids will reveal to you a whole new world that you never knew existed.

Translated from the Greek language, “comet” means “long-haired,” since ancient people associated a star with a long tail with hair developing in the wind.

Comets are dirty ice

The tail of a comet is formed only in close proximity to the Sun. Away from this celestial body, comets are icy, dark objects.

90% of a comet is ice, dirt and dust. In the center is a stone core. As it approaches the Sun, the ice melts, forming a dust cloud behind it. We see this tail.

Incredible quantity

The smallest comets reach a nucleus diameter of 16 km. The largest recorded is 40 km. Tails can be very long. For example, comet Hyakutake had a tail length of 580 million km.

A cluster of comets can number in the trillions. That's how much is in the Oort Cloud - a cluster that surrounds the solar system. Inside the solar system, astrologers count at least 4,000 comets.

Jupiter, as the largest planet in the solar system, is able to change the direction of comets by the force of its gravity. So, once the comet Shoemaker-Levy 9 crashed into the atmosphere of Jupiter.

Shapeless asteroids

Cosmic bodies form a spherical shape under the influence of their gravity. Asteroids are too small to form a sphere, so they look like ellipsoids or dumbbells.

The integrity of the form is a rarity for an asteroid. More often it is a pile of compounds, which is held by its own weight. The accumulations contain coal, stone, iron, volcanic materials.

The diameter of the largest asteroid Cecera is 950 km.

If an asteroid enters a planet's atmosphere, it's a meteor. If it falls to the ground, then it is a meteorite.

Is there a threat to us?

Asteroids pose a potential threat to the planet, but modern technology can easily prevent this.

To imagine how an asteroid falls to the surface of the planet, look at

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Meteorites and asteroids

What are asteroids and meteorites?

A meteorite is a body of cosmic origin that has fallen onto the surface of a large celestial object.

Most meteorites found have a weight of several grams to several kilograms. The largest meteorites found are Goba (which, according to estimates, weighed about 60 tons). It is believed that 5-6 tons of meteorites fall on Earth per day, or 2 thousand tons per year.

Asteromide is a relatively small celestial body in the solar system, moving in orbit around the sun. Asteroids are significantly inferior in mass and size to planets, have an irregular shape, and do not have an atmosphere, although they may have satellites.

Where do meteorites come from?

Meteorites are of great value to science. Before the start of the space age, they were the only ones that made it possible to conduct direct laboratory studies of extraterrestrial matter.

Planets on their way, as it were, scoop out interplanetary "garbage". At the same time, the solar system is replenished with new portions of it as a result of collisions with each other and crushing of asteroids and comets. It is possible that new meteoric bodies are also born due to the bombardment of small planets by comets coming from the outskirts of the solar system. The trajectories of fragments of asteroids and comets can differ greatly from the orbits of the parent bodies. That is why in interplanetary space today countless cosmic dust particles, grains of sand, stones and blocks are moving in various orbits. All this "trifle" with a diameter of fractions of a millimeter to several meters, astronomers call meteor bodies or meteoroids. The orbits of some of them intersect with the earth, and sometimes meteoroids invade the atmosphere of our planet at speeds of tens of kilometers per second.

Asteroid formation

Astronomers have always wondered: why is there such a large distance between the orbits of Mars and Jupiter? They have been trying for three decades to find a new planet in this gap. On January 1, 1801, at the observatory on the island of Sicily, astronomer Giuseppe Piazzi saw a small star in the sky, which had not been in this place before, and it was moving.

The orbit of this nimble object was calculated and found to be beyond the orbit of Mars. They named the planet Ceres, after the ancient Roman goddess of fertility.

Soon, another small stellar body was discovered next to it, which was called Pallas. William Herschel proposed to call their new asteroids - "star-like".

Of the thousands of asteroids, only 98% orbit the Sun between the orbits of Mars and Jupiter. Due to the impact of the giant Jupiter, some groups of asteroids can come close to the Earth's orbit. However, today the Solar System is a very old and “balanced object”, and all the cataclysms that should have happened have already happened.

How did asteroids form? According to one of the hypotheses, they are the remains of the planet Phaeton destroyed by gravitational disturbances. But in fact, the total mass of all celestial bodies in the asteroid belt does not exceed 4% of the mass of the Moon. Modern theories claim that the asteroid belt is a product of the gravitational perturbations of Jupiter, which created a kind of cosmic "meat grinder" beyond the orbit of Mars.

There are asteroids in the solar system and beyond the orbit of Jupiter. They are concentrated in the so-called Kuiper belt, which is much wider and more massive than the asteroid belt beyond the orbit of Mars.

INTERESTING! Asteroids are shaped by collisions. Almost every object in space, including the Earth, was shaped in one way or another by a collision. Every celestial body has at least two craters on its surface. These collisions can destroy the asteroid or cause the asteroids to coalesce. The collision can cause changes in the orbit -- rotation or axial tilt. There is no way to know exactly how many asteroids there were 100 million years ago and how many more will come from such interactions and collisions.

When was the first meteorite (asteroid) seen?

The first asteroid - Ceres

1) First: Ceres - was discovered at the very beginning of the 19th century. Following him, several more similar small celestial bodies were discovered moving far from the Earth - between the orbits of Mars and Jupiter. And at the very end of the century, the first asteroid was found, the path of which ran relatively close to the earth's orbit. And then the idea of a collision began to take on visible features. The fact is that the nature of the movement of this asteroid, which first received the number 433, and later the name Eros, turned out to be unusual. Unlike its predecessors, located far from the earth - between Mars and Jupiter, it moved in such a way that its path crossed the orbit of Mars and approached the Earth's orbit closer than the orbits of neighboring large planets. The minimum distance between Eros and the Earth turned out to be 22.5 million km.

In 1932, the asteroid Apollo was discovered, the orbit of which, as it turned out, not only approaches the earth, but even crosses it. And after another 5 years, the Earth almost collided with the asteroid Hermes, flying at a distance only 1.6 times the "location" of the Moon. This small asteroid, 800 m in diameter, was noticed by astronomers only a few days before approaching the Earth, so it was not possible to accurately determine its orbit, and soon it completely disappeared from view. Scientists do not exclude its re-passage near our planet, but now it is unlikely to be as unexpected, since astronomers from different countries are constantly monitoring asteroids approaching the Earth.

Now more than 500 space objects with similar orbits are known. They, called near-Earth or near-Earth asteroids, are relatively small - only the two largest of them reach 30-40 km in diameter. It is believed that in addition to them, there are also many small, yet inaccessible objects for detection with a telescope. The total number of near-Earth asteroids is “estimated” at the moment at 5,000.

The fall of celestial bodies has been described since ancient times, but the first meteorite, the fall of which was officially recorded, dates back to 1492. A stone weighing 126 kg fell on the Upper Rhine in the town of Ensisheim. By order of the Emperor of the Holy Roman Empire, Maximilian, he was chained to the wall of the city temple, "so that he could not fly back into the sky." In total, since then, the fall of a little more than 1.1 thousand meteorites has been reliably recorded, and more than 5 thousand have been found. At the same time, the death of a person has never been documented so far. Only two cases of people being injured by meteorites are known - in 1954 in the USA and in 2004 in Great Britain.

The danger of meteorites and asteroids

Let us recall the existence of such heavy gas giants as Jupiter and Saturn. It was they who played the role of "defenders" of the Earth from an external threat - dangerous asteroids, deflecting them and attracting them to themselves with their strong gravitational fields. Thus, those celestial bodies that could in an instant interrupt all the development of life on our planet simply did not reach it.

Most of the asteroids did not reach the Earth, while some did fall to the surface of the planet. Such a phenomenon is spoken of as a meteoritic threat, a threat to the existence of terrestrial life. The most famous manifestation of such a threat was a meteorite that fell to Earth about 65 million years ago, which led to a radical change in all life on the planet, putting an end to the era of dinosaurs. The geological evidence for this reason is that throughout the planet there is a layer of clays with a high content of iridium, a substance very rare on Earth, but quite common in meteorites. Based on this, we can assume the following scenario of that catastrophe: upon impact, a fallen meteorite raised a huge amount of dust into the atmosphere, which blocked the sunlight for several years. As a result, the plants first died, and after them, the dinosaurs that fed on them .. But how relevant is the meteorite threat now, in our days? Let's give a simple example from modern reality: on June 7, 2006, a large meteorite fell in northern Norway. Astronomers estimate its mass at only a thousand kilograms, while the destruction caused by it is comparable to the explosion of the atomic bomb dropped on Hiroshima. What would happen if this meteorite fell not in a deserted area, but on a large city? The consequences of such a fall would be dire. The catastrophe would have happened even when the meteorite fell not on land, but in the sea - in this case, a tsunami wave would have formed that destroyed the coastal zones where millions of people live.

Despite the destruction caused by the fall of the "heavenly guests", science does not know the case for them to kill a person. The only person to have been hit by a meteorite today is a woman from Australia. In 1954, a 3.2 kg stone fell on her house, injuring her shoulder in the process.

meteorite asteroid

Interesting facts about meteorites and asteroids

1. Asteroids and planets celebrate a birthday together. The process that helped form the planets is called augmentation. At the beginning of the universe, if two bodies collided, they would form a larger body. Planets and asteroids were formed in this manner. Apparently the planets have accumulated more mass than most asteroids. But, as seen with the asteroid Ceres, which is a dwarf planet, some asteroids are very close to gaining enough mass to have the gravity to become planetary.

2. The asteroid is made of various materials. Asteroids are made from various minerals and substances. Their composition depends on the planet they did away with in the collision, and also on the chemical reactions they may have experienced as they circled the solar system. Asteroids closest to the Sun are mostly carboniferous, while those further away are silicate rock. Metallic asteroids are made of 80% iron, the rest is nickel combined with many other mixed metals such as iridium, palladium, platinum and gold. Some are also half silicate and half metal.

3. Most asteroids are covered in dust. This dust is called regolith. It is more rocky rubble, such dust and is the result of constant collisions between asteroids and any other body that crosses their path. The larger object wins and is covered in rubble from the object that lost the fight.

4. An asteroid may have killed the dinosaurs. The Chicxulub crater is thought to be 65 million years old. It is possibly the source of the climate change that led to the extinction of all dinosaurs. One can imagine what fragments and clouds of dust must have been ejected into the air after this asteroid, large enough to create a crater that is over 180 km in diameter. Those dinosaurs that didn't die immediately probably suffered from starvation before they died.

5. Asteroids have satellite moons. The Galileo spacecraft proved this point back in 1993 when it investigated the flight of asteroid 243 (Ida) and discovered its lunar dactyl. It was the first non-planet object found with its own "moon". Since then, several other similar objects have been discovered, but the first discovery was the most exciting for astronomy.

Here are just a few interesting facts about asteroids. Some of the craters on Earth have been developed as sources of minerals. Sudbury is now one of the largest mining communities in the world. An incident near the Tunguska River in Siberia is believed by astronomers to be the newest asteroid impact on Earth.

meteorites

The very first mentions

Our ancestors have long known about the fall of meteorites on the planet. The ancient Greek philosophers Anaxagoras and Diogenes wrote about these events. By the way, in the first millennium BC, the Romans even minted images of meteorites on their coins.

In Russian chronicles, the fall of "heavenly stones" was first mentioned in 1091. An entry from the Laurentian Chronicle reads: “In the same summer, Vsevolod was catching the acting beasts behind Vyshegorod, sweeping the net and calling out to the cry, the great serpent fell from heaven, horrified by all the people. At the same time, I will knock the earth, as if hearing many ... ".

The oldest. The oldest of all known meteorites was discovered in China in the city of Xi'an. A two-ton alien fell to earth about 1.9 billion years ago.

The biggest. In 1920, a meteorite weighing 60 tons, called Goba, fell in Namibia. It consists entirely of iron and is the heaviest of all that have found refuge on Earth.

The most mysterious. To this day, the most mysterious case of a meteorite falling to earth is undoubtedly the Tunguska phenomenon. According to one version, a certain body of cometary origin caused an air explosion that occurred in the area of the Podkamennaya Tunguska River on June 30, 1908. The total energy of the explosion is estimated at 40-50 megatons of TNT, which corresponds to the energy of the most powerful hydrogen bomb! A generally accepted hypothesis explaining all the features of this phenomenon has not been proposed. At the moment, there are about 120 versions of the explanation of what happened.

The strongest meteor showers. It happened on the night of November 12-13, 1833. The rain continued continuously for 10 hours. During this time, approximately 240 thousand large and small meteorites fell on the Earth's surface.

The largest collection of meteorites on Earth. For meteorite hunters, an ideal place is the ice shell of Antarctica, which has preserved their black traces against its white background. According to experts, about 700 thousand are scattered inside and on the surface! The largest accumulation of meteorites on a limited area of the surface of Antarctica was discovered in 1979. According to the popular magazine New Scientist, "Meteorites are literally lying underfoot."

The largest collection of meteorites in the world. A rich collection is collected in the Mining Museum of St. Petersburg. The exhibits are more than 300 celestial aliens. The largest specimen on display is a 450-kilogram part of the aforementioned giant Sikhote-Alin meteorite that broke into pieces over the Ussuri taiga in 1947.

The most unexpected discovery of a meteorite. A certain Hawthorne, an amateur astronomer, built a private observatory on his estate near Washington. His favorite pastime was watching the falling heavenly bodies. In January 1955, he heard a sound like an explosion. Running into the observatory, Gawthorne saw two smoking fragments on his chair. They turned out to be meteorites. One of the fragments weighed 1192 grams, the other - 1132. Heavenly stones consisted of the purest iron.

Symbolic meteorite fall. September 5, 1812, on the eve of the Battle of Borodino, in the camp of the Russian artillery battery near the village of Gorki, a meteorite fell, as if announcing the impending victory. He was picked up by a sentry and handed over to his commander, Dietrichs. Then the find was kept in his family for a long time, and only in 1892 the descendants transferred it to the Russian Academy of Sciences.

The most useful "alien". The first iron used by man was meteoric. This is reflected in the names of many peoples. So, the ancient Egyptians called it "binipet", which means heavenly ore. In ancient Mesopotamia, it was called "anbar" - heavenly metal; the ancient Greek "sideros" comes from the Latin word - starry. The ancient Armenian name for iron is "yerkam" - fallen from the sky.

Literature

1. http://sky24.ru/analytics

2. http://starmission.ru/blog/planetary_system

3. http://skybox.org.ua/interesnye-fakty-ob-asteroidakh

4. http://galspace.spb.ru/nature.file/osvoenie.html

5. http://www.ronl.ru/reference/astronomiya/13155/

6. http://www.kommersant.ru/doc/2129498

7. http://www.xn--80audhgvl.xn--p1ai/

8. http://ru.wikipedia.org

9. http://www.mgdvorec.ru

10. http://www.meteorite.narod.ru

11. http://www.astrogalaxy.ru/061.html

12. http://www.coolreferat.com/

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mysterious space

Questions that constantly arise during contemplation require answers, and heavenly riddles require clues and scientific explanations. Here, for example, what is the difference between an asteroid and a meteorite? Not every student (and even an adult) can immediately answer this question. But let's start in order.

asteroids

To understand how an asteroid differs from a meteorite, you need to define the concept of "asteroid". This word from the ancient Greek language is translated as “like a star”, since these celestial bodies, when observed through a telescope, resemble stars rather than planets. Asteroids until 2006 were often called minor planets. Indeed, the movement of asteroids as a whole does not differ from the planetary movement, because it also occurs around the Sun. Asteroids differ from ordinary planets in their small size. For example, the largest asteroid Ceres is only 770 km across.

Where are these star-like space dwellers located? Most asteroids move in long-studied orbits in the space between Jupiter and Mars. But some small planets still cross the orbit of Mars (like the asteroid Icarus) and other planets, and sometimes even come closer to the Sun than Mercury.

meteorites

Unlike asteroids, meteorites are not inhabitants of space, but its messengers. Each of the earthlings can see the meteorite with their own eyes and touch it with their own hands. A large number of them are kept in museums and private collections, but it must be said that meteorites look rather unattractive. Most of them are gray or brownish-black pieces of stone and iron.

So, we managed to figure out how an asteroid differs from a meteorite. But what can unite them? It is believed that meteorites are fragments of small asteroids. Stones rushing in space collide with each other, and their fragments sometimes reach the surface of the Earth.

The most famous meteorite in Russia is the Tunguska meteorite, which fell in the deep taiga on June 30, 1908. In the recent past, namely in February 2013, the Chelyabinsk meteorite attracted everyone's attention, whose numerous fragments were found near Chebarkul Lake in the Chelyabinsk region.

Thanks to meteorites, peculiar guests from outer space, scientists, and with them all the inhabitants of the Earth, have an excellent opportunity to learn about the composition of celestial bodies and get an idea of the origin of the universe.

Meteora

The words "meteor" and "meteorite" come from the same Greek root, meaning "heavenly" in translation. We know, and how it differs from a meteor is not difficult to understand.

A meteor is not a specific celestial object, but an atmospheric phenomenon that looks like It occurs when fragments of comets and asteroids burn up in the Earth's atmosphere.

A meteor is a shooting star. It may appear to observers to fly back into outer space or burn up in the Earth's atmosphere.

Understanding how meteors differ from asteroids and meteorites is also easy. The last two celestial objects are concretely tangible (even if theoretically in the case of an asteroid), and the meteor is a glow resulting from the combustion of cosmic fragments.

Comets

No less wonderful celestial body that an earthly observer can admire is a comet. How are comets different from asteroids and meteorites?

The word "comet" is also of ancient Greek origin and literally translates as "hairy", "shaggy". Comets come from the outer part of the solar system, and, accordingly, have a different composition than asteroids that formed near the Sun.

In addition to the difference in composition, there is a more obvious difference in the structure of these celestial bodies. When approaching the Sun, a comet, unlike an asteroid, exhibits a nebulous coma shell and a tail consisting of gas and dust. Volatile substances of the comet, as they heat up, actively stand out and evaporate, turning it into the most beautiful luminous celestial object.

In addition, asteroids move in orbits, and their movement in outer space resembles the smooth and measured movement of ordinary planets. Unlike asteroids, comets are more extreme in their movements. Its orbit is highly elongated. The comet either approaches the Sun closely, or moves away from it at a considerable distance.

A comet differs from a meteorite in that it is in motion. A meteorite is the result of a collision of a celestial body with the earth's surface.

The heavenly world and the earthly world

It must be said that watching the night sky is doubly pleasant when its unearthly inhabitants are well known and understandable to you. And what a pleasure to tell your interlocutor about the world of stars and unusual events in outer space!

And it’s not even about the question of how an asteroid differs from a meteorite, but about the awareness of the close connection and deep interaction between the earthly and cosmic worlds, which must be established as actively as the relationship between one person and another.

Asteroids. Meteorites. Meteora.

Asteroid

ASTEROID - a small planet-like celestial body of the solar system, moving in orbit around the sun. Asteroids, also known as minor planets, are much smaller 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 the planets, which, when observed through a telescope, look like disks. The exact definition of the term "asteroid" is still not established. The term "minor planet" (or "planetoid") is not suitable for the definition of asteroids, as 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 larger than 50m in diameter, separating them from meteoroids that look like large rocks or may be even smaller. The classification is based on the assertion that asteroids can survive entering the Earth's atmosphere and reach its surface, while meteors, as a rule, completely burn up in the atmosphere.

As a result, an "asteroid" can be defined as an object of the solar system, consisting of solid materials, which is larger than a meteor in size.

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 precise orbits and were given an official number. 14077 of them at that moment had officially approved names. It is assumed that in the solar system there may be from 1.1 to 1.9 million objects larger than 1 km. Most of the currently known asteroids are concentrated within the asteroid belt located between the orbits of Mars and Jupiter.

Ceres was considered the largest asteroid in the solar system, measuring approximately 975 × 909 km, but since August 24, 2006, it has 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 seen with the naked eye. Asteroids moving in other orbits can also be observed during the period of passage near the Earth (eg 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 Hygiea (3%) - 51%, that is, the absolute majority asteroids have negligible mass.

Exploring asteroids

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

At the end of the 18th century, Franz Xaver von Zach organized a group of 24 astronomers. Since 1789, this group has been looking for a planet, which, according to the Titius-Bode rule, should have been 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 the stars in the area of the zodiac constellations at a certain moment. In subsequent nights, the coordinates were checked, and objects that moved a greater distance were highlighted. The estimated displacement of the planet being sought must have been about 30 arc seconds per hour, which should have been easily noticed.

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

However, Karl Ludwig Henke persisted, and in 1830 he resumed the search for new asteroids. Five years later, he discovered Astrea, the first new asteroid in 38 years. He also discovered Hebe less than two years later. After that, 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: Wolf single-handedly discovered 248 asteroids, starting with 323 Brucium, while a little more than 300 had been discovered before him. Now, a century later, only a few thousand asteroids have been identified, numbered and named. Much more are known about them, but scientists don't worry too much about studying them, calling asteroids 'vermin of the skies'.

Naming asteroids

At first, the asteroids were given the names of the heroes of Roman and Greek mythology, later the discoverers got the right to call it whatever they like, 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 every asteroid can get a name, but only one whose orbit is more or less reliably calculated. There have been cases when an asteroid was given a name decades after its discovery. Until an orbit has been computed, the asteroid is given a serial number reflecting the date it was discovered, such as 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 above example, this is the second half of February). The second letter indicates the serial number of the asteroid in the indicated 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 return to the beginning of the alphabet again, attributing the second letter index 2, next return - 3, and so on.

After receiving the 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 most of the numbered minor planets (98%) are located between the orbits of the planets Mars and Jupiter. Their average distances from the Sun are between 2.2 and 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 are, depending on the distance, from three to nine years. It is easy to calculate that the linear velocity is approximately equal to 20 km/s. The orbits of many minor planets are noticeably elongated. Eccentricities rarely exceed 0.4, but, for example, the asteroid 2212 Hephaestus has it equal to 0.8. Most of the orbits are located close to the ecliptic plane, i.e. to the plane of the Earth's orbit. The slopes 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 closely approach 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 Aton. The Amur family includes asteroids whose orbits at perihelion almost touch the orbit of the Earth. The Apollos cross the Earth's orbit from the outside, their perhelion distance is less than 1 AU. The "Atonians" have orbits with a semi-major axis smaller than the earth's and cross the earth's orbit from the inside. Representatives of all these families can meet the Earth. As for close passages, they happen quite often.

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

Most of the 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. studied how three bodies move under the influence of gravitational forces. The problem is very complex and has not yet been solved in general terms. However, Lagrange managed to find that in the system of three gravitating bodies (Sun - planet - small body) there are five points where the motion of a small body is 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. Asteroids - "Greeks" (Achilles, Ajax, Odysseus, etc.) are ahead of Jupiter by 60 °, "Trojans" follow at the same distance behind. According to estimates, the number of asteroids near the 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 in large telescopes under excellent atmospheric conditions, using very complex, laborious techniques, it is possible to obtain rather fuzzy 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 precise instruments that measure gloss, i.e. the stellar magnitude of the heavenly body. In addition, the illumination created by the Sun on an asteroid is well known. Other things being equal, the brightness of an asteroid is determined by the area of its disk. It is necessary, however, to know how much light a given surface reflects. This reflectivity is called albedo. Methods have been developed for its determination by the polarization of light from asteroids, 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.

Minor planets - asteroids(Greek asteroedeis - star-like) have nothing in common with stars, but 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 XVIII century. the empirical law of planetary distances (the so-called Titius-Bode rule) was known, 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 the asteroids are moving, long photographic exposures show them as bright white lines against the black background of the starry sky.

Observations have shown that asteroids have an irregular polyhedral shape and move along orbits of various shapes - from circles to highly elongated ellipses; the vast majority of them (98%) are enclosed 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 to Saturn. The orbits of most asteroids are concentrated near the plane of the ecliptic; their circulation periods are from 3.5 to 6 years; it is assumed that they rotate around their axes (based on the periodic change in apparent brightness). According to the material composition, stone, carbonaceous and metallic asteroids are distinguished.

The total mass of all asteroids is estimated at 0.01 Earth masses. Their general attraction does not cause perceptible perturbations in the motion of Mars and other planets.

The orbits of some asteroids intersect with the orbit of the Earth, but the probability of both the Earth and the asteroid being at the same point and colliding is extremely small. It is believed that 65 million years ago an asteroid-type celestial body 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. So, in May 1996, two asteroids flew by at a short distance from the Earth. Many experts suggest that the solar system fell into a kind of plume 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 emanating from 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 facilities, including those deployed in outer 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 amount of astronomical information in recent years, after observations were transferred from the Earth's surface to the near space.

On the question of the origin of asteroids, two directly opposite points of view were expressed. According to one hypothesis, asteroids are fragments of a large planet (it was called Phaeton), which was located between Mars and Jupiter at the site of the main asteroid belt and split 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 dusty environment, which could not unite into a planet due to the perturbing action of Jupiter. In both cases, the "culprit" is Jupiter.

Comets(Greek kometes - long-haired) - small bodies of the solar system moving in highly elongated elliptical or even parabolic orbits. Some comets have perihelion near the Sun and aphelion outside Pluto. The movement of comets in orbits can be both direct and reverse. The planes of their orbits lie in different directions from the Sun. The periods of revolution of comets are very different: from several years to many thousands of years. A tenth of the known comets (about 40) have appeared repeatedly; they are called periodic.

Comets have heads and tails. The head consists of a hard core and coma. The core is an ice conglomerate of frozen gases (steam, 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 and organic molecules. Comet nuclei are small, their diameter is from several hundred meters to several (50-70) kilometers. Coma is a gas-dust environment (hydrogen, oxygen, etc.) that glows when approaching the Sun. Near the perihelion, from the nucleus of a comet, under the influence of solar heat and corpuscular flows, “evaporation” (sublimation) of frozen gases occurs and a luminous tail of a comet is formed, sometimes more than one. It consists of rarefied gases and small solid particles and is directed away from the Sun. The length of the tails reaches hundreds of millions of kilometers. The Earth has more than once fallen into the tails of comets, for example, in 1910. This then caused great concern for 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), 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 the period of revolution (about 76 years). It was in its tail that the Earth ended up 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 irregularly shaped body about 15 by 7 km in size, around which a giant hydrogen corona with a diameter of 10 million km was discovered.

Comets are short-lived celestial bodies, because as they approach the Sun, they gradually “melt” due to the intense outflow of gases or disintegrate into a swarm of meteors. The meteor matter is subsequently more or less evenly distributed over the entire orbit of the parent comet. In this regard, the history of the periodic (about 7 years) comet Biela, discovered in 1826, is interesting. Twice after the discovery, astronomers observed its appearance, and for the third time, in 1846, they managed to fix its division into two parts, which during subsequent returns became more and more distant from each other. Then the meteor matter of the comet was stretched over the entire orbit, at the intersection of which the Earth observed a plentiful "rain" of meteors.

No exact data has been recorded that the Earth has ever collided with the nucleus of a comet. No more than five comets enter the Earth's orbit every year. However, there is a version that the famous Tunguska "meteorite", which fell in 1908 in the Podkamennaya Tunguska river basin, near the village of Vanavara, is a small (about 30 m) fragment of the Encke comet nucleus, which exploded as a result of thermal heating in the atmosphere, and "ice " and solid impurities "evaporated". At the same time, an explosive air wave knocked down a forest in an area within a radius of 30 km.

In 1994, scientists observed the fall of the comet Shoemaker-Levy on 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. During the explosions, a giant hot cloud arose 20 thousand km in size and a temperature of 30,000 ° C. The fall of such a comet to Earth would have ended in a cosmic catastrophe for it.

It is believed that the "comet cloud" surrounding the Sun formed along with the solar system. Therefore, by studying the substance of comets, scientists obtain information about the primary material from which planets and satellites were formed. In addition, assumptions have appeared about the "participation" of comets in the origin of life on Earth, since radiospectroscopic methods have proved the presence of complex organic compounds (formaldehyde, cyanoacetylene, etc.) in comets and meteorites.

Meteora, usually called “shooting stars”, are the smallest (mg) solid particles that fly into the atmosphere at a speed of up to 50-60 km / s, heat up due to air friction up 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 crack and even explode during flight. This 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 single meteors randomly appearing in the sky and groups of meteors in the form of meteor showers are fixed, within which particles move parallel to each other, although in perspective they seem to scatter from a single point in the sky, called the radiant. Meteor showers are named after the constellations in which their radiants are located. The Earth crosses the orbit of the Perseids around August 12, Orionids - October 20, Leonids - November 18, etc. Meteor showers move along the orbits of those asteroids or comets, as a result of the decay of which they are formed. The orbits of meteor showers are carefully studied for the safety of spacecraft and vehicles.

meteorites(from the Greek meteora - celestial phenomena) are called large meteoroids that fall to Earth. About two thousand meteorites with a total mass of about 20 tons fall on the earth's surface every year. 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 include mainly silicate minerals, and iron stone, consisting of a mixture of these substances. There are two groups of stony meteorites: chondrites (granular meteorites) and achondrites (earthy meteorites). Stony meteorites predominate. 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 meteorite Goba measuring 2.75 by 2.43 m weighing 59 tons was found in southwestern Africa, it is iron. The Sikhote-Alin meteorite (fell in 1947) split into thousands of pieces in the air and fell to Earth like an "iron rain". The total weight of the collected fragments is about 23 tons, they created 24 impact craters from 8 to 26 m in diameter. The Kaaba meteorite (“Black Stone”) is stored in the mosque of Mecca in Saudi Arabia and serves as an object of worship for Muslims. Many meteorites have been found in Antarctica, they are also found in the sediments of the World Ocean bed.

a – relative frequency of fallout of meteorites of different classes (according to J. Wood); 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 that bombarded the Earth was huge 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 still survived in the form of ring-shaped geological structures called astroblems (“stellar scars”). They are especially well visible from space. They reach tens of kilometers in diameter. The study of meteorites makes it possible to judge the structure and properties of celestial bodies and completes our knowledge of the internal structure of the Earth.

Literature.

Lyubushkina S.G. General geography: Proc. allowance for university students enrolled in special. "Geography" / S.G. Lyubushkina, K.V. pashkang, A.V. Chernov; Ed. A.V. Chernov. - M. : Education, 2004. - 288 p.

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