What parts does a comet consist of? Comets

Word "comet" is of Greek origin. You can translate it as "caudate" , "hairy" , "shaggy" .


This definition accurately characterizes a celestial body, since a “tail” of gas and dust is a characteristic feature of most comets.

A comet is a celestial body that, relative to other bodies in outer space, has a relatively small mass, usually of irregular shape, and contains frozen gases and non-volatile components.

Comets move through space in specific orbits. The comet's orbit around the Sun is an extremely elongated ellipse. Depending on the distance from the star the comet is, its appearance changes.

Far from the Sun, the comet looks like a blurry cloud. When approaching it, under the influence of solar thermal energy, the comet begins to evaporate gas. The gas blows away the particles of solid matter that make up the comet, and they take the form of a cloud around the nucleus, forming a coma. It happens that the coma swells to enormous sizes.


Due to evaporation and the action of the solar wind, the comet “grows” a tail of dust and gas, which is how it got its name.

Characteristics of comets

Conventionally, a comet can be divided into three parts - the nucleus, the coma, and the tail. Everything in comets is absolutely cold, and their glow is only the reflection of sunlight by dust and the glow of gas ionized by ultraviolet light.

Core

The core is the heaviest part of this celestial body. The bulk of the comet is concentrated in it. The composition of the comet's nucleus is quite difficult to accurately study, since at a distance accessible to a telescope, it is constantly surrounded by a gas mantle. In this regard, the theory of the American astronomer Whipple was adopted as the basis for the theory about the composition of the comet's nucleus.

According to his theory, the comet's nucleus is a mixture of frozen gases mixed with various dust. Therefore, when a comet approaches the Sun and heats up, the gases begin to “melt”, forming a tail. However, there are other assumptions about the composition of the core.

One of them claims that the comet has a loose structure of dust with very large pores - a kind of cosmic “sponge”. The “sponge” is incredibly fragile: if you take even a very large piece of the comet, you can easily tear it apart with just your hands.

Tail

The tail of a comet is its most expressive part. It is formed by a comet as it approaches the Sun. The tail is a luminous strip that stretches from the core in the direction opposite to the Sun, “blown” by the solar wind.

It consists of gases and dust that evaporate from the comet's nucleus under the influence of the same solar wind. The tail glows brightly - thanks to it we have the opportunity to observe the flight of these celestial bodies.

Differences between comets

Comets differ from each other in mass and size. Some of them are heavier, others are lighter, but still these celestial bodies are very small compared to other bodies in the Universe. In addition, the observer (if he is very lucky) can see that different comets have different luminosities and shapes. It depends on what gases evaporate from the surface of their cores.

The tail of comets can also have different lengths and shapes. For some, it stretches across the entire visible sky: in 1680, the inhabitants of the Earth could observe a Great Comet with a tail of 240 million kilometers. Some comets have a straight and narrow tail, others have a slightly curved and wide tail, deviating to the side; still others are short and distinctly curved.

Differences between comets and asteroids

Asteroids, like comets, are small celestial bodies. However, asteroids are larger than comets: according to the international classification, they include bodies whose diameter exceeds 30 m. Until 2006, the asteroid was even called a minor planet. This was indirectly facilitated by the fact that asteroids have satellites.

Asteroids and comets have a number of other differences from each other.

Firstly, an asteroid and a comet differ in their composition. An asteroid consists primarily of metals and rocks, while a comet, as we already know, consists of frozen gases and dust.


This leads to the second difference - the asteroid does not have a tail, since there is nothing to evaporate from its surface. Unlike comets, asteroids move in a circular orbit and tend to unite into belts.

And lastly, there are several million known asteroids, while there are only 3,572 comets.

Classification and types of comets

Planet designations

Until 1994, comets were first given temporary designations, consisting from the year of their opening And latin small letter, which indicates the order of their opening in a given year(for example, Comet 1969i was the ninth comet discovered in 1969).

After the comet passed perihelion, its orbit was reliably established, after why the comet received a permanent designation, consisting of the year of passage of perihelion and a Roman numeral, indicating the order of passage of perihelion in a given year. So comet 1969i was given a permanent designation 1970 II(the second comet to pass perihelion in 1970).

Since 1994, the name of the comet includes the year of discovery, a letter indicating the half of the month in which the discovery occurred, and the number of discovery in that half of the month. Before the comet designation put a prefix, indicating on the nature of the comet. The following prefixes are used:

Comet designations since 1994

Example: C/1995 O1 Long-period comet /1995/1 discovered in August

Sizes and shape of comets

When astronomers talk about the size of a comet, they mean size of the comet's nucleus. The sizes of comets vary widely. Typically, comet nuclei do not exceed 10-15 km in diameter, and most often have dimensions of 1-5 km. Comet Lovejoy had a nucleus 120 m in diameter, comet Hale-Bopp had a nucleus at least 70 km in diameter. But such comets are very rare

Classification of cometary orbits

Comet ISON is a long-period circumsolar comet

Orbit and speed

The figure shows the elliptical orbits of the two comets, as well as the nearly circular orbits of the planets and a parabolic orbit. At the distance that separates the Earth from the Sun, the circular speed is 29.8 km/s, and the parabolic speed is 42.2 km/s.

Near Earth, the speed of Comet Encke is 37.1 km/s, and the speed of Comet Halley is 41.6 km/s; This is why Comet Halley goes much further from the Sun than Comet Encke.

The movement of the comet's nucleus is completely determined by the attraction of the Sun. The shape of the comet's orbit depends on its speed and distance to the Sun.

(v p) = 1.4 v c - parabolic orbit

The average speed of a body is inversely proportional to the square root of its average distance to the Sun (a). If the speed is always perpendicular to the radius vector directed from the Sun to the body, then the orbit is circular, and the speed is called circular speed (vc) at a distance a.

The speed of escape from the gravitational field of the Sun along a parabolic orbit ( v p) is 1.4 times the circular speed at this distance. If the comet's speed is less v p, then it moves around the Sun in an elliptical orbit and never leaves the Solar System.

But if the speed exceeds v p, then the comet passes by the Sun once and leaves it forever, moving in a hyperbolic orbit

Comets of the Solar System have always been of interest to space researchers. The question of what these phenomena are also worries people who are far from studying comets. Let's try to figure out what this celestial body looks like and whether it can influence the life of our planet.

Contents of the article:

A comet is a celestial body formed in Space, the size of which reaches the scale of a small settlement. The composition of comets (cold gases, dust and rock fragments) makes this phenomenon truly unique. The comet's tail leaves a trail of millions of kilometers. This spectacle fascinates with its grandeur and leaves more questions than answers.

The concept of a comet as an element of the solar system

Let's take a closer look at the features of comets:

• Comets are so-called snowballs that pass through their orbit and contain dusty, rocky and gaseous accumulations.
• The celestial body warms up during the period of approach to the main star of the solar system.
• Comets do not have satellites that are characteristic of planets.
• Formation systems in the form of rings are also not typical for comets.
• It is difficult and sometimes unrealistic to determine the size of these celestial bodies.
• Comets do not support life. However, their composition can serve as a certain building material.

Features of the structure of comets

The description of a comet can be divided into characteristics of the nucleus, coma and tail of the object. This suggests that the celestial body under study cannot be called a simple structure.

Comet nucleus

There are 3 theories that consider the structure of comet nuclei differently:

1. The "dirty snowball" theory. This assumption is the most common and belongs to the American scientist Fred Lawrence Whipple. According to this theory, the solid part of the comet is nothing more than a combination of ice and fragments of meteorite matter. According to this specialist, a distinction is made between old comets and bodies of a younger formation. Their structure is different due to the fact that more mature celestial bodies repeatedly approached the Sun, which melted their original composition.
2. The core consists of dusty material. The theory was announced at the beginning of the 21st century thanks to the study of the phenomenon by the American space station. Data from this exploration indicate that the core is a dusty material of a very friable nature with pores occupying the majority of its surface.
3. The core cannot be a monolithic structure. Further hypotheses diverge: they imply a structure in the form of a snow swarm, blocks of rock-ice accumulation and meteorite accumulation due to the influence of planetary gravity.

Comet coma

Three levels of coma can be defined, which look like this:

• Interior chemical, molecular and photochemical composition. Its structure is determined by the fact that the main changes occurring with the comet are concentrated and most activated in this area. Chemical reactions, decay and ionization of neutrally charged particles - all this characterizes the processes that occur in an internal coma.
• Coma of radicals. It consists of molecules that are active in their chemical nature. In this area there is no increased activity of substances, which is so characteristic of an internal coma. However, here too the process of decay and excitation of the described molecules continues in a calmer and smoother mode.
• Coma of atomic composition. It is also called ultraviolet. This region of the comet's atmosphere is observed in the hydrogen Lyman-alpha line in the distant ultraviolet spectral region.

Comet tail

Fedor Bredikhin proposed classifying sparkling plumes into the following subspecies:

1. Straight and narrow format tails. These components of the comet are directed from the main star of the solar system.
2. Slightly deformed and wide-format tails. These plumes are evading the Sun.
3. Short and severely deformed tails. This change is caused by a significant deviation from the main star of our system.

• Dust tail. A distinctive visual feature of this element is that its glow has a characteristic reddish tint. A plume of this format is homogeneous in its structure, stretching for a million, or even tens of millions of kilometers. It was formed due to numerous dust particles that the energy of the Sun threw to a long distance. The yellow tint of the tail is due to the dispersion of dust particles by sunlight.
• Tail of the plasma structure. This plume is much more extensive than the dust trail, because its length is tens and sometimes hundreds of millions of kilometers. The comet interacts with the solar wind, which causes a similar phenomenon. As is known, solar vortex flows are penetrated by a large number of fields of a magnetic nature. They, in turn, collide with the comet's plasma, which leads to the creation of a pair of regions with diametrically different polarities. At times, this tail breaks off spectacularly and a new one is formed, which looks very impressive.
• Anti-Tail. It appears according to a different pattern. The reason is that it is directed towards the sunny side. The influence of the solar wind on such a phenomenon is extremely small, because the plume contains large dust particles. It is possible to observe such an antitail only when the Earth crosses the comet’s orbital plane. The disc-shaped formation surrounds the celestial body on almost all sides.

Main types of comets

1. Short-period comets. The orbital time of such a comet does not exceed 200 years. At their maximum distance from the Sun, they have no tails, but only a subtle coma. When periodically approaching the main luminary, a plume appears. More than four hundred such comets have been recorded, among which there are short-period celestial bodies with a revolution around the Sun of 3-10 years.
2. Comets with long orbital periods. The Oort cloud, according to scientists, periodically supplies such cosmic guests. The orbital term of these phenomena exceeds the two hundred year mark, which makes the study of such objects more problematic. Two hundred and fifty such aliens give reason to believe that in fact there are millions of them. Not all of them are so close to the main star of the system that it becomes possible to observe their activities.

The most famous comets of the solar system

There are a large number of comets that pass through the solar system. But there are the most famous cosmic bodies that are worth talking about.

Halley's Comet

Of course, some long-period comets are more spectacular, but 1P/Halley can be observed even with the naked eye. This factor makes this phenomenon unique and popular. Almost thirty recorded appearances of this comet pleased outside observers. Their frequency directly depends on the gravitational influence of large planets on the life activity of the described object.

The speed of Halley's comet in relation to our planet is amazing because it exceeds all indicators of the activity of the celestial bodies of the Solar System. The approach of the earth's orbital system to the comet's orbit can be observed at two points. This results in two dusty formations, which in turn form meteorite showers called the Aquarids and Oreanids.

If we consider the structure of such a body, it is not much different from other comets. When approaching the Sun, the formation of a sparkling trail is observed. The comet's nucleus is relatively small, which may indicate a pile of debris as building material for the object's base.

You will be able to enjoy the extraordinary spectacle of the passage of Halley's Comet in the summer of 2061. It promises better visibility of the grandiose phenomenon compared to the more than modest visit in 1986.

The phenomenality of this discovery lies in the fact that in the late 90s the comet was observed without special equipment for ten months, which in itself cannot but surprise.

The shell of the solid core of a celestial body is quite heterogeneous. Icy areas of unmixed gases are combined with carbon monoxide and other natural elements. The discovery of minerals that are characteristic of the structure of the earth's crust and some meteorite formations once again confirm that Comet Hale-Bop originated within our system.

The influence of comets on the life of planet Earth

The Icelandic volcano Eyjafjallajokull began its active and destructive two-year activity, which surprised many scientists of the time. This happened almost immediately after the famous Emperor Bonaparte saw the comet. This may be a coincidence, but there are other factors that make you wonder.

The previously described Comet Halley strangely affected the activity of such volcanoes as Ruiz (Colombia), Taal (Philippines), Katmai (Alaska). The impact of this comet was felt by people living near the Cossuin volcano (Nicaragua), which began one of the most destructive activities of the millennium.

Comet Encke caused a powerful eruption of the Krakatoa volcano. All this may depend on solar activity and the activity of comets, which provoke some nuclear reactions when approaching our planet.

Comet impacts are quite rare. However, some experts believe that the Tunguska meteorite belongs to just such bodies. They cite the following facts as arguments:

• A couple of days before the disaster, the appearance of dawns was observed, which, with their diversity, indicated an anomaly.
• The appearance of such a phenomenon as white nights in unusual places immediately after the fall of a celestial body.
• The absence of such an indicator of meteoricity as the presence of solid matter of a given configuration.

What a comet looks like - look at the video:

At distances of the order of 100,000 a.m. That is, a huge number of small bodies are moving, representing lumps of stuck together dust particles, shrouded in hydrogen, water and hydrocarbon snow. The collection of these bodies is called the “cloud of comets”, or Oort cloud.

It was formed simultaneously with the Solar system about 5 billion years ago, i.e. the substance from which the planets were formed was preserved in comets. Therefore, studying comets is very important. Individual bodies move in the cloud with very low relative speeds (fractions of a meter per second). Random collisions can lead to compaction of bodies, their sticking together or destruction.

As a result of very long processes, most cloud bodies acquire dimensions of several, perhaps several tens, kilometers. Under the influence of ionizing radiation and cosmic rays (which are streams of elementary particles of high energy), complex chemical reactions take place in the “snow”, and over billions of years complex chemical compounds arise in it. These bodies later become the solid nuclei of comets.

Periodically, as a result of random collisions or disturbances from nearby stars, a body from a cloud of comets can be thrown into the central regions of the Solar System. If at the same time there is a rapprochement with one of the giant planets, then a case is possible (and sometimes occurs) when this body moves into an orbit passing in close proximity to the Sun.

A comet is distinguished by a head - a luminous nebulous shell with increasing brightness towards the center, where a brighter core is usually observed, and an extended tail, always directed away from the Sun.

Comet tail

At a distance approximately equal to the distance from the Sun to Jupiter, the surface of the comet's solid nucleus heats up so much that frozen gases begin to evaporate. As it approaches the Sun, evaporation increases and a luminous gas cloud forms. Under the influence of light pressure and solar wind, gases begin to move away from the Sun and the comet appears tail, also directed from the Sun. After passing the point of the orbit closest to the Sun, the temperature on the surface of the solid core drops, evaporation decreases and the tail gradually disappears (Fig. 56). Material from the site

When approaching the Sun, only low-melting components evaporate. Silicate and iron dust particles remain, and a dust crust appears on the surface, well protecting the internal regions of the core from excessive heating.

As is clearly seen in periodic comets, the amount of gas evaporated by the comet decreases with each passage near the Sun. The strength of the core decreases and the comet is destroyed.

The disintegration of a comet was directly observed in comet Biela (1848). A few years after the final destruction of the comet, the Earth crossed its orbit. These days there was an exceptional meteor shower. More than 1,000 meteors appeared per minute; observers said that in Berlin at that time it became so light that it was possible to read.

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 ephemeris). 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 solar wind plasma, observable radiation appears in the UV and X-ray regions of the 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, 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 importance 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 play an important role in the evolution of the Earth and other terrestrial planets 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 of primary forms of 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.

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