What is a comet: stories of discoveries, the most famous comets. Modern research on comets New scientific information about comets

Since ancient times, people have sought to uncover the secrets that the sky holds. Since the first telescope was created, scientists have been gradually collecting grains of knowledge that are hidden in the boundless expanses of space. It's time to find out where the messengers from space - comets and meteorites - came from.

What is a comet?

If we examine the meaning of the word "comet", we come to its ancient Greek equivalent. Literally it means “with long hair.” Thus, the name was given in view of the structure of this Comet, which has a “head” and a long “tail” - a kind of “hair”. The head of a comet consists of a nucleus and perinuclear substances. The loose core may contain water, as well as gases such as methane, ammonia and carbon dioxide. The comet Churyumov-Gerasimenko, discovered on October 23, 1969, has the same structure.

How the comet was previously represented

In ancient times, our ancestors revered her and invented various superstitions. Even now there are those who associate the appearance of comets with something ghostly and mysterious. Such people may think that they are wanderers from another world of souls. Where did this come from? Perhaps the whole point is that the appearance of these heavenly creatures ever coincided with some unkind incident.

However, as time passed, the idea of ​​what small and large comets were changed. For example, a scientist like Aristotle, studying their nature, decided that it was a luminous gas. After a while, another philosopher named Seneca, who lived in Rome, suggested that comets are bodies in the sky moving in their orbits. However, real progress in their study was achieved only after the creation of the telescope. When Newton discovered the law of gravity, things took off.

Current ideas about comets

Today, scientists have already established that comets consist of a solid core (from 1 to 20 km in thickness). What does the comet's nucleus consist of? From a mixture of frozen water and cosmic dust. In 1986, photographs of one of the comets were taken. It became clear that its fiery tail is an emission of a stream of gas and dust, which we can observe from the earth's surface. For what reason does this “fiery” emission occur? If an asteroid flies very close to the Sun, then its surface heats up, which leads to the release of dust and gas. Solar energy exerts pressure on the solid material that makes up the comet. As a result, a fiery tail of dust is formed. This debris and dust is part of the trail that we see in the sky when we observe the movement of comets.

What determines the shape of a comet's tail?

The post on comets below will help you better understand what comets are and how they work. They come in different varieties, with tails of all sorts of shapes. It's all about the natural composition of the particles that make up this or that tail. Very small particles quickly fly away from the Sun, and larger ones, on the contrary, tend to the star. What is the reason? It turns out that the former move away, pushed by solar energy, while the latter are affected by the gravitational force of the Sun. As a result of these physical laws we get comets whose tails are curved in different ways. Those tails that are largely composed of gases will be directed away from the star, while corpuscular tails (consisting mainly of dust), on the contrary, will tend to the Sun. What can you say about the density of a comet's tail? Cloud tails can typically measure millions of kilometers, in some cases hundreds of millions. This means that, unlike the body of a comet, its tail consists largely of discharged particles, having practically no density. When an asteroid approaches the Sun, the comet's tail can bifurcate and acquire a complex structure.

The speed of particle movement in a comet's tail

Measuring the speed of movement in a comet's tail is not so easy, since we cannot see individual particles. However, there are cases when the speed of movement of matter in the tail can be determined. Sometimes gas clouds can condense there. From their movement, the approximate speed can be calculated. So, the forces moving the comet are so great that the speed can be 100 times greater than the gravity of the Sun.

How much does a comet weigh?

The entire mass of comets largely depends on the weight of the comet's head, or more precisely, its nucleus. Presumably, the small comet could weigh only a few tons. Whereas, according to forecasts, large asteroids can reach a weight of 1,000,000,000,000 tons.

What are meteors

Sometimes one of the comets passes through the Earth's orbit, leaving a trail of debris in its wake. When our planet passes by the place where the comet was, these debris and cosmic dust remaining from it enter the atmosphere at great speed. This speed reaches more than 70 kilometers per second. When the comet's fragments burn up in the atmosphere, we see a beautiful trail. This phenomenon is called meteors (or meteorites).

Age of comets

Fresh asteroids of enormous size can survive in space for trillions of years. However, comets, like any other one, cannot exist forever. The more often they approach the Sun, the more they lose the solid and gaseous substances that make up their composition. “Young” comets can lose a lot of weight until a kind of protective crust forms on their surface, which prevents further evaporation and burning out. However, the “young” comet ages, and the nucleus becomes decrepit and loses its weight and size. Thus, the surface crust acquires many wrinkles, cracks and breaks. Gas streams, burning, push the body of the comet forward and forward, giving speed to this traveler.

Halley's Comet

Another comet, the structure is the same as the comet Churyumov - Gerasimenko, is an asteroid, discovered. He realized that comets have long elliptical orbits along which they move at large intervals of time. He compared comets that were observed from the earth in 1531, 1607 and 1682. It turned out that it was the same comet, which moved along its trajectory after a period of time equal to approximately 75 years. In the end, she was named after the scientist himself.

Comets in the Solar System

We are in the solar system. At least 1000 comets have been found near us. They are divided into two families, and they, in turn, are divided into classes. To classify comets, scientists take into account their characteristics: the time during which they are able to travel the entire path in their orbit, as well as the period from orbit. If we take Halley's Comet mentioned earlier as an example, it completes a full revolution around the sun in less than 200 years. It belongs to periodic comets. However, there are those that travel the entire path in much shorter periods of time - the so-called short-period comets. We can be sure that in our solar system there are a huge number of periodic comets, the orbits of which pass around our star. Such celestial bodies can move so far from the center of our system that they leave Uranus, Neptune and Pluto behind. Sometimes they can come very close to planets, causing their orbits to change. An example is Comet Encke.

Comet Information: Long Period

The trajectory of long-period comets is very different from short-period comets. They go around the Sun from all sides. For example, Heyakutake and Hale-Bopp. The latter looked very spectacular when last time were approaching our planet. Scientists have calculated that the next time they can be seen from Earth will be thousands of years later. A lot of comets with a long period of movement can be found at the edge of our solar system. Back in the mid-20th century, a Dutch astronomer suggested the existence of a cluster of comets. Over time, the existence of a cometary cloud was proven, which is known today as the “Oort Cloud” and was named after the scientist who discovered it. How many comets are there in the Oort Cloud? According to some assumptions, at least a trillion. The period of movement of some of these comets can be several light years. In this case, the comet will cover its entire path in 10,000,000 years!

Fragments of Comet Shoemaker-Levy 9

Reports of comets from all over the world help in their research. Astronomers could observe a very interesting and impressive vision in 1994. More than 20 fragments remaining from Comet Shoemaker-Levy 9 collided with Jupiter at crazy speed (approximately 200,000 kilometers per hour). Asteroids flew into the planet's atmosphere with flashes and huge explosions. The hot gas caused the formation of very large fire spheres. The temperature to which they were heated chemical elements, several times higher than the temperature recorded on the surface of the Sun. After which a very high column of gas could be seen through telescopes. Its height reached enormous dimensions - 3200 kilometers.

Comet Biela - a double comet

As we have already learned, there is plenty of evidence that comets break up over time. Because of this, they lose their brightness and beauty. There is only one example of such a case that can be considered - Biela's comet. It was first discovered in 1772. However, it was subsequently noticed more than once again in 1815, then in 1826 and in 1832. When it was observed in 1845, it turned out that the comet looked much larger than before. Six months later it turned out that it was not one, but two comets that were walking next to each other. What happened? Astronomers have determined that a year ago the Biela asteroid split in two. This is the last time scientists have recorded the appearance of this miracle comet. One part of it was much brighter than the other. She was never seen again. However, over time, a meteor shower, the orbit of which exactly coincided with the orbit of Comet Biela, caught the eye more than once. This incident proved that comets are capable of disintegrating over time.

What happens during a collision

For our planet, a meeting with these celestial bodies does not bode well. A large piece of comet or meteorite, approximately 100 meters in size, exploded high in the atmosphere in June 1908. As a result of this disaster, many reindeer died and two thousand kilometers of taiga were destroyed. What would happen if such a block burst over big city such as New York or Moscow? This would cost the lives of millions of people. What would happen if a comet with a diameter of several kilometers hit the Earth? As mentioned above, in mid-July 1994 it was “bombarded” with debris from comet Shoemaker-Levy 9. Millions of scientists watched what was happening. How would such a collision end for our planet?

Comets and the Earth - ideas of scientists

Information about comets known to scientists sows fear in their hearts. Astronomers and analysts paint terrible pictures in their minds with horror - a collision with a comet. When an asteroid enters the atmosphere, it will cause destruction within the cosmic body. It will explode with a deafening sound, and on Earth you can see a column of meteorite debris - dust and stones. The sky will be covered in a fiery red glow. There will be no vegetation left on Earth, since all forests, fields and meadows will be destroyed due to the explosion and fragments. Due to the fact that the atmosphere will become impenetrable to sunlight, it will become sharply cold, and plants will not be able to carry out photosynthesis. This will disrupt the nutritional cycles. sea ​​creatures. Being without food for a long time, many of them will die. All of the above events will also affect natural cycles. Widespread acid rain will have a detrimental effect on the ozone layer, making it impossible to breathe on our planet. What will happen if a comet falls into one of the oceans? Then this can lead to disastrous environmental disasters: the formation of tornadoes and tsunamis. The only difference will be that these cataclysms will be on a much larger scale than those that we could experience in several thousand years of human history. Huge waves of hundreds or thousands of meters will sweep away everything in their path. There will be nothing left of towns and cities.

"No need to worry"

Other scientists, on the contrary, say that there is no need to worry about similar disasters. According to them, if the Earth comes close to a celestial asteroid, this will only lead to illumination of the sky and meteor shower. Should we worry about the future of our planet? Is it likely that we will ever be met by a flying comet?

Comet fall. Should you be afraid?

Can you trust everything that scientists present? Do not forget that all the information about comets recorded above is just theoretical assumptions that cannot be verified. Of course, such fantasies can sow panic in the hearts of people, but the likelihood that something similar will ever happen on Earth is negligible. Scientists who study our solar system are amazed at how well thought out everything is in its design. It is difficult for meteorites and comets to reach our planet because it is protected by a giant shield. The planet Jupiter, due to its size, has enormous gravity. Therefore, it often protects our Earth from passing asteroids and comet remnants. The location of our planet leads many to believe that the entire device was thought out and designed in advance. And if this is so, and you are not a zealous atheist, then you can rest easy, because the Creator will undoubtedly preserve the Earth for the purpose for which he created it.

Names of the most famous

Reports about comets from various scientists from all over the world make up a huge database of information about cosmic bodies. Among the particularly well-known are several. For example, comet Churyumov - Gerasimenko. In addition, in this article we could get acquainted with the comet Fumeaker-Levy 9 and Halley. In addition to them, comet Sadulayev is known not only to sky researchers, but also to amateurs. In this article, we tried to provide the most complete and verified information about comets, their structure and contact with other celestial bodies. However, just as it is impossible to embrace all the expanses of space, it will not be possible to describe or list all known at the moment comets. Brief information about the comets of the solar system is presented in the illustration below.

Sky exploration

The knowledge of scientists, of course, does not stand still. What we know now was not known to us some 100 or even 10 years ago. We can be sure that man's tireless desire to explore the vastness of space will continue to push him to try to understand the structure of celestial bodies: meteorites, comets, asteroids, planets, stars and other more powerful objects. We have now penetrated into such vastness of space that contemplating its immensity and unknowability is awe-inspiring. Many agree that all this could not have appeared on its own and without a purpose. Such a complex design must have an intention. However, many questions related to the structure of space remain unanswered. It seems that the more we learn, the more reasons we have to explore further. In fact, the more information we acquire, the more we understand that we do not know our Solar System, our Galaxy, and even more so the Universe. However, all this does not stop astronomers, and they continue to struggle with the mysteries of existence. Each comet flying nearby is of particular interest to them.

Computer program “Space Engine”

Fortunately, today not only astronomers can explore the Universe, but also ordinary people whose curiosity prompts them to do so. Not long ago, a program for computers called “Space Engine” was released. It is supported by most modern mid-range computers. It can be downloaded and installed completely free of charge using an Internet search. Thanks to this program, information about comets will also be very interesting for children. It presents a model of the entire Universe, including all comets and celestial bodies that are known to modern scientists today. To find a space object of interest to us, for example, a comet, we can use the oriented search built into the system. For example, you need comet Churyumov - Gerasimenko. In order to find it, you need to enter its serial number 67 R. If you are interested in another object, for example, comet Sadulayev. Then you can try entering its name in Latin or entering its special number. Thanks to this program you can learn more about space comets.

Artem Novichonok,
Researcher at the Petrozavodsk State University Observatory,
discoverer of two comets and several dozen asteroids
“Trinity Option” No. 21(165), October 21, 2014

1. Comets are one of the types of small bodies in the Solar System. They owe their name to the characteristic tails that “bloom” near the Sun. In Greek κομήτης means “hairy”, “having long hair" Even the astronomical symbol for a comet (☄) has the shape of a disk, from which three lines extend, like hair.
2. The periods of revolution of comets around the Sun range over a wide range - from several years to several million years. Based on this, comets are divided into short- and long-period. The orbits of the latter are highly elongated, the minimum possible distance of the comet from the Sun can practically coincide with the surface of the star, and the maximum can be tens of thousands of astronomical units.
3. The main part of a comet is the nucleus. The size of the nuclei is relatively small - up to several tens of kilometers. The cores consist of a loose mixture of rocks, dust and fusible substances (frozen H 2 O, CO 2, CO, NH 3, etc.). Comet nuclei are very dark - they reflect only a few percent of the light falling on them.
4. As a comet approaches the Sun, the surface temperature of its core increases, causing ice of different compositions to sublimate. The coma (atmosphere) of the comet is formed, which, together with the nucleus, makes up the head of the comet. The size of the coma can reach several million kilometers.
5. When approaching the Sun, the comet also forms a tail, consisting of coma particles moving away from the nucleus. There are two types of tails: ion (gas) tails, which are always directed in the direction opposite to the Sun due to the action of the solar wind, and dust tails, “spreading” along the comet’s orbit with relatively small deviations. The length of a comet's tail can reach hundreds of millions of kilometers.
6. As a result of cometary activity, a fair amount of small celestial bodies - meteor particles - remain in the comet's orbit. If the comet's orbit is close enough to the Earth's orbit, a meteor shower may be observed - many meteors ("shooting stars") visible in a short period of time. During heavy meteor showers, thousands of meteors can be observed per hour.
7. Since comets are constantly losing matter, they cannot exist in the active phase for a long time and, over time, disintegrate into fragments, completely turn into interplanetary dust, or, having lost the supply of near-surface fusible substances, become inert asteroid-like objects.
8. Every year, dozens of comets are discovered coming to us from the outskirts of the solar system. Consequently, there (at distances up to 50–100 thousand AU) there is a large reservoir of cometary nuclei - the Oort cloud. It cannot be observed directly, but comets provide compelling evidence of its existence.
9. In the Middle Ages, comets caused fear among people and were considered harbingers of tragic events in the lives of nations (wars, epidemics) and royalty. And even the appearance of Comet Hale-Bopp in 1997 is notorious for the mass suicides of members of the Heaven's Gate sect.
10. Very bright comets appear infrequently. But they are certainly among the most beautiful and impressive objects in the sky. It is enough to mention, for example, the Great Comet of 1861, C/1995 O1 (Hale-Bopp), which was easily observed even in cities in the spring of 1997, or comet C/2006 P1 (McNaught), which was observed in January 2007, including in during the daytime, and at dusk it showed a huge fan-shaped tail.

Comets interest many people. These celestial bodies captivate young and older people, women and men, professional astronomers and simply amateur astronomers. And our portal site offers the latest news about the latest discoveries, photos and videos of comets, as well as much more useful information, which you can find in this section.

Comets are small celestial bodies revolving around the Sun along a conical section with a rather extended orbit, having a hazy appearance. As a comet approaches the Sun, it forms a coma and sometimes a tail of dust and gas.

Scientists suggest that comets periodically fly into the solar system from the Oort cloud, since it contains many cometary nuclei. As a rule, bodies located on the outskirts of the solar system consist of volatile substances (methane, water and other gases), which evaporate as they approach the Sun.

To date, more than four hundred short-period comets have been identified. Moreover, half of them were in more than one perihelion passage. Most of them belong to families. For example, many short-period comets (they orbit the Sun every 3-10 years) form the Jupiter family. The families of Uranus, Saturn and Neptune are small in number (Halley's famous comet belongs to the latter).

Comets that come from the depths of Space are nebulous objects with a tail trailing behind them. It often reaches several million kilometers in length. As for the comet's nucleus, it is a body of solid particles shrouded in a coma (foggy envelope). A core with a diameter of 2 km can have a coma 80,000 km across. The sun's rays dislodge gas particles from the coma and throw them back, pulling them into a smoky tail moving behind her in outer space.

The brightness of comets largely depends on their distance from the Sun. Of all the comets, only a small part approaches the Earth and the Sun so much that they can be seen with the naked eye. Moreover, the most noticeable of them are usually called “great (large) comets.”

Most of the “shooting stars” (meteorites) we observe are of cometary origin. These are particles lost by a comet, which burn up when they enter the atmosphere of a planet.

Nomenclature of comets

Over the years of studying comets, the rules for naming them have been clarified and changed many times. Until the early 20th century, many comets were simply named by the year they were discovered, often with additional clarification regarding the season of the year or brightness if there were several comets in that year. For example, “Great September Comet of 1882”, “Great January Comet of 1910”, “Day Comet of 1910”.

After Halley was able to prove that comets 1531, 1607 and 1682 were the same comet, it was named Halley's Comet. He also predicted that in 1759 she would return. The second and third comets were named Bela and Encke in honor of the scientists who calculated the orbit of the comets, despite the fact that the first comet was observed by Messier, and the second by Mechain. A short time later, periodic comets were named after their discoverers. Well, those comets that were observed only during one perihelion passage were named, as before, by the year of appearance.

At the beginning of the twentieth century, when comets began to be discovered more often, a decision was made on the final naming of comets, which has been preserved to this day. Only when the comet was identified by three independent observers did it receive a name. Many comets in recent years is discovered through tools that are discovered by entire teams of scientists. Comets in such cases are named after their instruments. For example, comet C/1983 H1 (IRAS - Araki - Alcock) was discovered by the IRAS satellite, George Alcock and Genichi Araki. In the past, another team of astronomers discovered periodic comets, to which a number was added, for example, comets Shoemaker-Levy 1 - 9. Today, a huge number of planets are discovered by a variety of instruments, which made this system impractical. Therefore, it was decided to resort to a special system for naming comets.

Until early 1994, comets were given temporary designations that consisted of the year of discovery plus a Latin lowercase letter indicating the order in which they were discovered in that year (for example, comet 1969i was the 9th comet to be discovered in 1969). Once the comet passed perihelion, its orbit was established and it received a permanent designation, namely the year of perihelion passage plus a Roman numeral, which indicates the order of perihelion passage in that year. For example, comet 1969i was given the permanent designation 1970 II (meaning it was the second comet to pass perihelion in 1970).

As the number of discovered comets increased, this procedure became very inconvenient. Therefore, the International Astronomical Union adopted in 1994 new system designations of comets. Today, the name of comets includes the year of discovery, the letter indicating the half of the month in which the discovery took place, and the number of the discovery itself in that half of the month. This system is similar to the one used to name asteroids. Thus, the fourth comet, which was discovered in 2006, was designated 2006 D4 in the second half of February. A prefix is ​​also placed before the designation. He explains the nature of the comet. It is customary to use the following prefixes:

· C/ is a long-period comet.

· P/ - short-period comet (one that was observed in two or more perihelion passages, or a comet whose period is less than two hundred years).

· X/ - a comet for which it was not possible to calculate a reliable orbit (most often for historical comets).

· A/ - objects mistakenly taken for comets, but turned out to be asteroids.

· D/ - comets were lost or destroyed.

The structure of comets

Gas components of comets

Core

The nucleus is the solid part of the comet where almost all of its mass is concentrated. At the moment, the nuclei of comets are not available for study, since they are hidden by the constantly forming luminous matter.

The core, according to the most common Whipple model, is a mixture of ice with the inclusion of particles of meteoric matter. The layer of frozen gases, according to this theory, alternates with dust layers. As the gases heat up, they evaporate and carry clouds of dust with them. Thus, the formation of dust and gas tails in comets can be explained.

But according to the results of studies carried out using an American automatic station in 2015, the core is made up of loose material. This is a lump of dust with pores that occupy up to 80 percent of its volume.

Coma

Coma is a light, foggy shell surrounding the core, consisting of dust and gases. Most often it stretches from 100 thousand to 1.4 million km from the core. Under high pressure light is deformed. As a result, it is elongated in the antisolar direction. Together with the nucleus, the coma forms the head of the comet. Typically a coma consists of 4 main parts:

• internal (chemical, molecular and photochemical) coma;
• visible coma (or also called radical coma);
• atomic (ultraviolet) coma.

Tail

As they approach the Sun, bright comets form a tail - a weak luminous stripe, which most often, as a result of the action of sunlight, is directed away from the Sun towards the opposite side. Despite the fact that the coma and tail contain less than one millionth of the comet's mass, almost 99.9% of the glow that we see as the comet passes through the sky consists of gas formations. This is because the core has a low albedo and is itself very compact.

The tails of comets can differ in both shape and length. For some, they stretch across the entire sky. For example, the comet's tail, which was seen in 1944, was 20 million km long. Even more impressive is the length of the tail of the Great Comet of 1680, which was 240 million km. There have also been cases where the tail is separated from the comet.

The tails of comets are almost transparent and do not have sharp outlines - stars are clearly visible through them, since they are formed from super-rarefied matter (its density is much less than the density of gas from a lighter). As for the composition, it is varied: tiny particles of dust or gas, or a mixture of both. The composition of most dust grains resembles asteroid materials, as revealed by the Stardust spacecraft's study of comet 81P/Wilda. We can say that this is “visible nothing”: we can see the tails of comets only because the dust and gas glow. Moreover, the combination of gas is directly related to its ionization by UV rays and streams of particles that are ejected from the solar surface, and dust scatters sunlight.

At the end of the 19th century, astronomer Fyodor Bredikhin developed the theory of shapes and tails. He also created a classification of comet tails, which is still used in astronomy today. He proposed classifying comet tails into three main types: narrow and straight, directed away from the Sun; curved and wide, deviating from the central luminary; short, strongly inclined from the Sun.

Astronomers explain such different shapes of comet tails as follows. The constituent particles of comets have different properties and composition and react differently to solar radiation. Therefore, the paths of these particles in space “diverge,” as a result of which the tails of space travelers take on different shapes.

Study of comets

Humanity has shown interest in comets since ancient times. Their unexpected appearance and unusual appearance have served as a source of various superstitions for many centuries. The ancients associated the appearance in the sky of these cosmic bodies with a brightly glowing tail with the onset of difficult times and impending troubles.

Thanks to Tycho Brahe, during the Renaissance, comets began to be classified as celestial bodies.

People gained a more detailed understanding of comets thanks to the 1986 trip to Halley's comet on spacecraft such as Giotto, as well as Vega-1 and Vega-2. Instruments installed on these devices transmitted images of the comet's nucleus and various information about its shell to Earth. It turned out that the comet's nucleus is composed mainly of plain ice(with minor inclusions of methane and carbon dioxide ice) and field particles. Actually, they form the shell of the comet, and as it approaches the Sun, some of them, under the influence of pressure from the solar wind and solar rays, turn into the tail.

According to scientists, the dimensions of the nucleus of Halley's comet are several kilometers: 7.5 km in the transverse direction, 14 km in length.

The nucleus of Halley's comet is irregular in shape and constantly rotates around an axis, which, according to Friedrich Bessel's assumptions, is almost perpendicular to the plane of the comet's orbit. As for the rotation period, it was 53 hours, which agreed well with the calculations.

NASA's Deep Impact spacecraft dropped a probe on Comet Tempel 1 in 2005, allowing it to image its surface.

Study of comets in Russia

The first information about comets appeared in the Tale of Bygone Years. It was clear that the chroniclers attached special importance to the appearance of comets, since they were considered harbingers of various misfortunes - pestilence, wars, etc. But in the language Ancient Rus' They were not given any separate name, since they were considered tailed stars moving across the sky. When the description of the comet appeared on the pages of the chronicles (1066), the astronomical object was called “a great star; star image of a copy; star... emitting rays, which is also called the sparkler.”

The concept of “comet” appeared in Russian after the translation of European works that dealt with comets. The earliest mention was seen in the collection “Golden Beads,” which is something like an entire encyclopedia about the world order. At the beginning of the 16th century, "Lucidarius" was translated from German language. Since the word was new for Russian readers, the translator explained it with the familiar name “star”, namely “the star of the comita gives shine from itself like a ray.” But the concept of “comet” entered the Russian language only in the mid-1660s, when comets actually appeared in the European sky. This event aroused particular interest. From translated works, the Russians learned that comets are not much like stars. Until the beginning of the 18th century, the attitude towards the appearance of comets as signs was preserved both in Europe and in Russia. But then the first works appeared that denied the mysterious nature of comets.

Russian scientists mastered European scientific knowledge about comets, which allowed them to make a significant contribution to their study. Astronomer Fyodor Bredinich in the second half of the 19th century built a theory of the nature of comets, explaining the origin of tails and their bizarre variety of shapes.

For all those who want to get acquainted with comets in more detail and learn about current news, our portal website invites you to follow the materials in this section.

Theories of the origin of comets

Today there is no single theory of the origin of comets accepted by all experts. Actually, this is the first mystery of these celestial bodies - how, where and under the influence of what factors do they appear? According to one of the hypotheses, which is quite ancient, but still has its supporters today, comets are formed from materials that are ejected as a result of volcanic activity from the bowels of the giant planets of the Solar system, Jupiter and Saturn. A more modern hypothesis puts forward a distant part of the solar system, the so-called Oort cloud, as the homeland of comets, in which, according to assumptions, comets formed simultaneously with the planets. There they supposedly remain until the attraction of the sun and planets gradually pulls out one comet at a time, which begin their space journey . There is also an opinion that comets generally come from outside the solar system, so it is still difficult to establish the mechanism of their formation in the conditions of modern development of space exploration

Visibility and invisibility of comets

The philistine consciousness firmly compares comets with a celestial body that has a long and extensive trail or tail. Comets are indeed often characterized by the presence of such tails. But it turns out that if a comet’s trail is not visible, this does not mean that it does not exist. Whether or not a comet's tail is visible and how bright and extensive it is depends primarily on the proximity of a particular comet to the Sun. The mechanism of the influence of the solar wind on the particles that make up the so-called cloudy body of the comet, which moves along with the nucleus, is not yet clear to scientists. However, the fact remains that as they approach the Sun, the visibility of comets and the brightness of their trails increase significantly. Versions have been put forward that this mechanism is akin to the mechanism of resonant fluorescence or the Aurora Borealis, but so far these are only hypotheses.

Dust in the eyes of scientists

The cloudy body of comets consists, among other things, of cosmic dust - this is an obvious fact for all space researchers. However, it was recently discovered that part of the cosmic dust that makes up the comet was formed under the influence of high temperatures. And this is a mystery for scientists, because the main part of comets is most often ice, both as the comet’s nucleus and ice dust in the tail of the celestial body. A reasonable question arises: how can even the icy core of a comet contain cosmic dust formed at high temperatures? It has already been suggested that comets are formed in different parts The solar system is made of materials that have differences in physical properties, including those that absorb thermal energy with different intensities during their movement through outer space.

Space “weather forecast”: also no guarantees...

For teachers of the Earth, comets are divided, first of all, by the periodicity of their orbits, into which they fall at a certain moment and begin their movement relative to the Sun. This division allows us to distinguish between short-period (orbital duration less than 150 years), medium-period (orbital duration from 150 to 200 years) and long-period (orbital duration over 200 years) comets. The problem is that any comet, literally at any moment, can significantly change the trajectory of its movement and, consequently, the direction and duration of its orbit. Because comets are very susceptible to the gravitational influence of the planets they pass near, and changes in the trajectory of their movement under these influences cannot be predicted. A small planet like the Earth also imparts a certain correction to the orbits of closely passing comets, so what can we say about a giant, for example, Jupiter. Therefore, scientists, of course, make the trajectories of comets, and at the same time make forecasts for them, but these calculations always have a considerable share of relativity.

Comets with unusual behavior

One of the most extravagant assumptions regarding the part of comets is the hypothesis that some celestial objects that astronomers have identified as comets are actually alien spaceships . Most often, comet Denning is named as a “suspect,” which supposedly, in a manner suspicious for a comet, alternately described circles around Jupiter, Venus, Mars and the earth (as if these were familiarization flights). Also often mentioned is the Aren-Roland comet, which supposedly had two tails, and in different directions - this dismisses the traditional reason for comet tails in the form of solar wind and suggests the presence of multi-directional rocket engines on the spacecraft. In response, representatives of official scientific departments provide data that long-term observation of these comets did not reveal any “special” signs.

COMETS (from the Greek κομήτης - hairy, shaggy), small in size and mass celestial bodies of the Solar System, revolving around the Sun in highly elongated orbits and sharply increasing their brightness when approaching the Sun. Near the Sun, comets appear in the sky as luminous balls with a long tail behind them (Fig. 1). Comets are icy celestial bodies (sometimes called cosmic icebergs) whose bright glow is created by the scattering of sunlight and other physical effects. The full names of comets include the names of the discoverers (no more than three), the year of discovery, a capital letter and number indicating at what point in the year the comet was discovered, and a prefix indicating the type of comet (P - short-period comet, C - long-period comet , D - collapsed comet, etc.). Every year, approximately 10-20 comets can be observed with an amateur telescope.

Historically, the appearance of comets in the sky was considered a bad omen, foreshadowing misfortune and disaster. Disputes about the nature of comets (atmospheric or cosmic) continued for 2 thousand years and ended only in the 18th century (see Comet astronomy). Significant progress in the study of comets was achieved in the 20th century thanks to spacecraft missions to comets.

General information about comets. Comets, together with asteroids, meteoroids and meteor dust, belong to the small bodies of the Solar System. The total number of comets in the Solar System is extremely large; it is estimated to be no less than 10 12 . comets are divided into two main classes: short-period and long-period with an orbital period of less than and more than 200 years, respectively. The total number of comets observed in historical times (including in parabolic and hyperbolic orbits) is close to 1000. Of these, about 100 short-period comets are known that regularly approach the Sun. The orbits of these comets have been reliably calculated. Such comets are called “old”, in contrast to “new” long-period comets, which, as a rule, were observed in the inner regions of the Solar System only once. Most short-period comets belong to the so-called families of giant planets, being in orbits close to them. The most numerous is the Jupiter family, numbering hundreds of comets, among which over 50 of the shortest-period comets are known with a period of revolution around the Sun from 3 to 10 years. Fewer comets observed include the families of Saturn, Uranus and Neptune; to the latter, in particular, belongs the famous Halley's comet.

The main reservoirs containing cometary nuclei are located on the periphery of the Solar System. This is the Kuiper belt, located near the ecliptic plane directly beyond the orbit of Neptune, within 30-100 AU. e. from the Sun, and a spherical Oort-shaped cloud, located approximately half the distance to the nearest stars (30-60 thousand au). The Oort cloud periodically experiences gravitational disturbances from giant interstellar gas-dust clouds, the galactic disk and stars (during random approaches) and therefore does not have a clearly defined outer boundary. Comets can leave the Oort cloud, replenishing the interstellar medium, and return again. Thus, comets play the role of unique probes of the regions of the Galaxy closest to the Solar System.

Due to similar disturbances, some bodies from the Oort cloud end up in the inner regions of the Solar System, moving into highly elliptical orbits. When approaching the Sun, these bodies are observed as long-period comets. Under the influence of gravitational disturbances from the planets (primarily Jupiter and other giant planets), they either join the known families of short-period comets that regularly return to the Sun, or move to parabolic and even hyperbolic orbits, leaving the Solar System forever. The main source of short-period comets is the Kuiper Belt. Due to Neptune's gravitational perturbations of Kuiper belt objects, a relatively small proportion of the icy bodies inhabiting the belt are constantly migrating into the inner regions of the Solar System.

The movement of comets in orbit. Comets move in orbits with high eccentricity and inclination to the ecliptic plane. The movement occurs both in the forward direction (like the planets) and in the opposite direction. Comets experience strong tidal disturbances when passing near planets, which leads to a significant change in their orbits (and, accordingly, difficulties in predicting the movements of comets and accurately determining ephemerides). As a result of these orbital changes, many comets fall into the Sun.

The results of calculations of the elements of the orbits of comets are published in special catalogs; for example, a catalog compiled in 1997 contains the orbits of 936 comets, over 80% of which were observed only once. Depending on their orbital position, the brightness of comets varies by several orders of magnitude, reaching a maximum shortly after perihelion and a minimum at aphelion. The absolute magnitude of comets is, to a first approximation, inversely proportional to R4, where R is the distance from the Sun. As a rule, short-period comets orbit the Sun no more than a few hundred times. Therefore, their lifespan is limited and usually does not exceed 100 thousand years.

The active phase of the comet's existence ends when the supply of volatile substances in the nucleus is exhausted or the surface of the comet's nucleus is covered with a melted dust-ice crust resulting from the comet's repeated approaches to the Sun. After the end of the active phase, the comet's nucleus becomes similar in physical properties to an asteroid, so there is no sharp boundary between asteroids and comets. Moreover, the opposite effect is also possible: an asteroid may begin to show signs of cometary activity when its surface crust cracks for one reason or another.

The irregularity of the orbits of comets leads to a poorly predicted probability of their collisions with planets, which further complicates the problem of the asteroid-comet hazard. The collision of the Earth with a fragment of a comet's nucleus may have caused the Tunguska event of 1908 (see Tunguska meteorite). In 1994, more than 20 fragments of comets Shoemaker-Levy 9 (torn apart in the immediate vicinity of the planet by tidal forces) were observed falling onto Jupiter (Fig. 2), which led to catastrophic phenomena in the atmosphere of Jupiter.

The structure and composition of comets. Comets consist of a nucleus, an atmosphere (coma) and a tail. Irregularly shaped nuclei have small sizes - from a few to tens of kilometers and, accordingly, a very small mass that does not have a noticeable gravitational effect on planets and other celestial bodies. Comet nuclei rotate about an axis almost perpendicular to the plane of their orbit, with a period from several units to several tens of hours. Comet nuclei are characterized by low reflectivity (albedo 0.03-0.04), so comets are not visible far from the Sun. The exception is Comet Encke: the orbital period of this comet is only 3.31 years, it moves relatively little away from the Sun and can be observed throughout its orbit.

The remaining elements of the cometary structure are formed as the comet approaches the Sun. Near the perihelion of the orbit, a coma occurs due to the sublimation of core matter and the removal of dust from its surface. The size of dust particles in a coma is mainly 10 -7 -10 -6 m, but larger particles are also present. The coma is a brightly glowing foggy shell with a diameter of over 100 thousand km. Inside the coma, in the vicinity of the nucleus, the brightest clump is identified - the head of the comet, and outside the coma - the hydrogen corona (halo). A tail stretches out from the coma, tens of millions of kilometers long: a relatively faintly luminous strip, which, as a rule, does not have clear outlines and is directed mainly in the direction opposite to the Sun. Intense sublimation and dust removal create a reactive force; this non-gravitational effect also influences the irregularity of cometary orbits.

Comet nuclei have a very low average density, usually not exceeding hundreds of kg/m3. This indicates the porous structure of the cores (Fig. 3), consisting mainly of water ice and some low-temperature condensates (carbon dioxide, ammonia, methane ice) with an admixture of silicates, graphite, metals, hydrocarbons and other organic compounds. A significant portion of the core consists of dust and larger rocky fragments. The abundance of water ice in comets is explained by the fact that water is the most common molecule in the solar system.

Measurements taken as spacecraft approached the comet generally confirmed the hypothesis that the nucleus is a “dirty snowball.” A similar model of cometary nuclei was proposed in the mid-20th century by the American astronomer F. Whipple. Coma consists mainly of neutral molecules of water, hydrogen, carbon (C 2, C 3), a number of radicals (OH, CN, CH, NH, etc.) and glows due to luminescence processes. It is partially ionized by short-wave solar radiation, creating ions OH +, CO +, CH +, etc. When these ions interact with the solar wind plasma, observable radiation appears in the UV and X-ray areas spectrum

During the sublimation of ice, dust is simultaneously intensively carried into the atmosphere, due to which the tail of the comet is mainly created. According to the classification proposed back in the 2nd half of the 19th century by F.A. Bredikhin, three types of cometary tails are distinguished: I - straight and narrow, directed in the direction opposite to the Sun; II - wide, curved and slightly deviated relative to the direction from the Sun; III - straight, short and strongly deviated from the direction from the Sun. In the 20th century, S. V. Orlov developed the physical basis of this classification in accordance with the mechanism of tail formation. The Type I tail is created by plasma interacting with the solar wind, the Type II tail is created by submicron-sized dust particles exposed to light pressure, and the Type III tail is created by a collection of small and larger particles experiencing different accelerations under the influence of gravitational forces and light pressure.

As a result of this formation mechanism, the position in space of type III tails is less clear; it does not coincide with the antisolar direction and is tilted back relative to the orbital motion. Sometimes curved lines are observed in the structure of the tail - the so-called syndinams, or even a fan of syndinams created by dust particles of different sizes.

The changes that occur with comets at different points of its orbit and during its life are largely determined by non-stationary processes of heat and mass transfer in the porous core and the formation of a heterogeneous surface structure from which sublimation occurs. Kinetic modeling of these processes made it possible to obtain an idea of ​​the state of the gas in a coma. Near the nuclei of active comets, the gas flow in the hemisphere facing the Sun is close to equilibrium; the gas density quickly decreases with distance from the surface of the nucleus. Due to the adiabatic expansion of gas into the interplanetary vacuum, the temperature is several kelvins at a distance from the core of about 100 km. In the vicinity of the symmetry axis, a well-defined jet (jet) is formed, caused by the intense removal of gas and dust. (In the image of the nucleus of Comet Halley, obtained when the Giotto spacecraft flew near it, several jets are visible.) Such uneven sublimation from the surface of the nucleus can be explained by thermal deformations causing faults and cracks in the surface crust of the comet.

As a result of the intense release of dust from short-period comets, dust tori are formed along its orbit. These tori are periodically crossed by the Earth in its orbital movement, which causes meteor showers.

The significance of comets for cosmogony. The origin of comets is probably associated with the gravitational ejection of icy bodies from the region of formation of the giant planets (see the article Cosmogony). Therefore, studies of comets contribute to solving the fundamental problem of the origin and evolution of the Solar System. Comets are of great scientific interest, primarily from the point of view of cosmochemistry, since they contain the primary substance from which the Solar system was formed. It is believed that comets and the most primitive class of asteroids (carbonaceous chondrites) retained particles of a protoplanetary cloud and a gas-dust accretion disk in their composition. As relics of the formation of planets (planetesimals), comets have undergone the least changes in the process of evolution. Therefore, information on the composition of comets makes it possible to impose fairly strict restrictions on the range of parameters used in the development of cosmogonic models.

At the same time, according to modern ideas, comets themselves could have played an important role in the evolution of the Earth and other planets terrestrial group as a source of volatile elements and their compounds (primarily water). As the results of mathematical modeling showed, from this source the Earth could receive an amount of water comparable to the volume of its hydrosphere. Venus and Mars could have received approximately the same amounts of water, which speaks in favor of the hypothesis of the existence of ancient oceans on them that were lost during subsequent evolution. Comets are also considered as possible carriers primary forms life. The problem of the emergence of life on planets is associated, in particular, with the transport of matter inside and outside the solar system and migration-collision processes, in which comets play a key role.

Lit.: Orlov S.V. On the nature of comets. M., 1960; Dobrovolsky O. V. Comets. M., 1966; Physics and chemistry of comets. IN.; N.Y., 1990; Yeomans D. Comets: a chronological history of observation; science, myth and folklore. N.Y., 1991; Comets in the post-Hailey era. Dordrecht, 1991. Vol. 1-2; Marov M. Ya. Physical properties and models of comets // Astronomical Bulletin. Research of the Solar System. 1994. T. 28. No. 4-5; aka. Small bodies of the Solar System and some problems of cosmogony // Advances in Physical Sciences. 2005. T. 175. No. 6.