Which group of cosmic bodies does a comet belong to? Some of the famous comets. Characteristics of comets and their difference from each other
The first appearance of a comet, which was registered in the chronicles, dates back to 2296 BC. And this was done by a woman, the wife of Emperor Yao, who had a son, who later became Emperor Ta-Yu, the founder of the Hia dynasty. It was from this moment that Chinese astronomers followed the night sky, and only thanks to them, we know about this date. The history of cometary astronomy begins with it. The Chinese not only described comets, but also marked the paths of comets on a star map, which allowed modern astronomers to identify the brightest of them, trace the evolution of their orbits, and obtain other useful information.
It is impossible not to notice in the sky a spectacle so rare when a misty luminary is seen in the sky, sometimes so bright that it can sparkle through the clouds (1577), eclipsing even the moon. Aristotle in the 4th century BC explained the phenomenon of the comet as follows: light, warm, "dry pneuma" (gases of the Earth) rises to the boundaries of the atmosphere, enters the sphere of heavenly fire and ignites - this is how "tailed stars" are formed. Aristotle argued that comets cause severe storms, drought. His ideas were universally recognized for two millennia. In the Middle Ages, comets were considered harbingers of wars and epidemics. So the Norman invasion of southern England in 1066 was associated with the appearance of Halley's comet in the sky. The fall of Constantinople in 1456 was also associated with the appearance of a comet in the sky. Studying the appearance of a comet in 1577, Tycho Brahe found that it was moving far beyond the orbit of the moon. The time has begun to study the orbits of comets ...
The first fanatic to discover comets was Charles Messier, an employee of the Paris Observatory. He entered the history of astronomy as a compiler of a catalog of nebulae and star clusters, intended to search for comets, so as not to mistake distant nebulous objects for new comets. For 39 years of observations, Messier discovered 13 new comets! In the first half of the 19th century, among the "catchers" of comets, Jean Pons especially distinguished himself. The watchman of the Marseille Observatory, and later its director, built a small amateur telescope and, following the example of his compatriot Messier, began searching for comets. The case turned out to be so exciting that in 26 years he discovered 33 new comets! It is no coincidence that astronomers have nicknamed it the "Comet Magnet". The record set by Pons still remains unsurpassed. About 50 comets are available for observations. In 1861, the first photograph of a comet was taken. However, according to archival data, an entry dated September 28, 1858 was found in the annals of Harvard University, in which George Bond reported on an attempt to obtain a photographic image of a comet at a focus of 15 "refractor! At a shutter speed of 6", the brightest part of the coma was worked out with a size of 15 arc seconds. The photo has not been saved.
The 1999 Comet Orbital Catalog contains 1722 orbits for 1688 cometary occurrences relating to 1036 different comets. From ancient times to the present day, about 2000 comets have already been observed and described. For 300 years after Newton, the orbits of more than 700 of them have been calculated. The general results are as follows. Most comets move in ellipses, moderately or strongly elongated. Comet Encke takes the shortest route from Mercury to Jupiter and back in 3.3 years. The most distant of those that were observed twice is a comet discovered in 1788 by Caroline Herschel and returning 154 years later from a distance of 57 AU. In 1914, Delavan's comet set out to break the distance record. It will retire at 170,000 AU. and "finishes" after 24 million years.
So far, more than 400 short-period comets have been discovered. Of these, about 200 have been observed in more than one perihelion passage. Many of them are included in the so-called families. For example, approximately 50 of the shortest period comets (their full revolution around the Sun lasts 3-10 years) form the Jupiter family. Slightly smaller than the families of Saturn, Uranus and Neptune (the latter, in particular, includes the famous comet Halley).
Terrestrial observations of many comets and the results of studies of Halley's comet using spacecraft in 1986 confirmed the hypothesis first put forward by F. Whipple in 1949 that comet nuclei are something like “dirty snowballs” several kilometers across. Apparently, they consist of frozen water, carbon dioxide, methane and ammonia with dust and stony matter frozen inside. When a comet approaches the Sun, the ice begins to evaporate under the influence of solar heat, and the escaping gas forms a diffuse luminous sphere around the nucleus, called a coma. A coma can reach a million kilometers across. The nucleus itself is too small to be directly visible. Observations in the ultraviolet range of the spectrum, carried out from spacecraft, have shown that comets are surrounded by huge clouds of hydrogen, many millions of kilometers in size. Hydrogen is obtained as a result of the decomposition of water molecules under the action of solar radiation. In 1996, the X-ray emission of Comet Hyakutake was discovered, and subsequently it was discovered that other comets are sources of X-rays.
Observations in 2001 by the Subara Telescope's High Dispersion Spectrometer allowed astronomers to measure the temperature of icy ammonia in a comet's nucleus for the first time. Temperature value in 28 + 2 degrees Kelvin suggests that comet LINEAR (C/1999 S4) formed between the orbits of Saturn and Uranus. This means that now astronomers can not only determine the conditions under which comets form, but also find the place of their origin. Using spectral analysis, organic molecules and particles were found in the heads and tails of comets: atomic and molecular carbon, carbon hybrid, carbon monoxide, carbon sulfide, methyl cyanide; inorganic components: hydrogen, oxygen, sodium, calcium, chromium, cobalt, manganese, iron, nickel, copper, vanadium. The molecules and atoms observed in comets are, in most cases, "debris" of more complex parent molecules and molecular complexes. The nature of the origin of parent molecules in cometary nuclei has not yet been unraveled. So far, it is only clear that these are very complex molecules and compounds like amino acids! Some researchers believe that such a chemical composition can serve as a catalyst for the emergence of life or the initial condition for its origin when these complex compounds enter the atmospheres or on the surfaces of planets with sufficiently stable and favorable conditions.
Solar system comets have always been of interest to space explorers. The question of what these phenomena are is of concern to people who are far from studying comets. Let's try to figure out what this celestial body looks like, whether it can affect the life of our planet.
The content 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 tail of a comet leaves a trail that is estimated at 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
To understand this concept, one should start from the orbits of comets. Many of these cosmic bodies pass through the solar system.
Consider in detail the features of comets:
- Comets are the so-called snowballs, passing along their orbit and containing dusty, rocky and gaseous accumulations.
- The heating of the celestial body occurs during the period of approach to the main star of the solar system.
- Comets do not have satellites, which are characteristic of planets.
- Systems of formations in the form of rings are also not characteristic of comets.
- The size of these celestial bodies is difficult and sometimes unrealistic to determine.
- 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 studied celestial body cannot be called a simple construction.
comet nucleus
Almost the entire mass of the comet lies precisely in the nucleus, which is the most difficult object to study. The reason is that the core is hidden even from the most powerful telescopes by the matter of the luminous plane.
There are 3 theories that differently consider the structure of the nucleus of comets:
- 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 substance. According to this specialist, old comets and bodies of a younger formation are distinguished. Their structure is different due to the fact that more mature celestial bodies repeatedly approached the Sun, which melted their original composition.
- The core is made 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. The data of this reconnaissance indicate that the core is a dusty material of a very loose nature with pores occupying most of its surface.
- The core cannot be a monolithic structure. Further, the hypotheses diverge: they imply a structure in the form of a snow swarm, blocks of rock-ice clusters and a meteorite heap due to the influence of planetary gravitations.
comet coma
Together with the nucleus, the head of the comet forms a coma, which is a hazy shell of light color. The plume of such a component of the comet stretches for a rather long distance: from one hundred thousand to almost one and a half million kilometers from the base of the object.
There are three levels of coma, which look like this:
- The inside of the chemical, molecular and photochemical composition. Its structure is determined by the fact that in this region the main changes occurring with the comet are concentrated and are most activated. Chemical reactions, decay and ionization of neutrally charged particles - all this characterizes the processes that take place in an internal coma.
- coma radicals. 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, even here 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 Lyman-alpha hydrogen line in the remote ultraviolet spectral region.
comet tail
The tail of a comet is a spectacle unique in its beauty and spectacularity. Usually it is directed from the Sun and looks like an elongated gas-dust plume. Such tails do not have clear boundaries, and it can be said that their color range is close to complete transparency.
Fedor Bredikhin proposed to classify sparkling plumes into the following subspecies:
- Straight and narrow tails. These components of the comet have a direction from the main star of the solar system.
- Slightly deformed and wide tails. These plumes evade the Sun.
- Short and severely deformed tails. Such a change is caused by a significant deviation from the main luminary 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, which the energy of the Sun threw over a long distance. The yellow hue of the tail is due to the scattering of dust particles by sunlight.
- Plasma structure tail. This plume is much more extensive than the dust plume, because its length is estimated at tens, and sometimes hundreds of millions of kilometers. The comet interacts with the solar wind, from which a similar phenomenon arises. As is known, solar vortex flows are penetrated by a large number of fields of the magnetic nature of the formation. 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 there is a spectacular break in this tail and the formation of a new one, which looks very impressive.
- anti-tail. It appears in a different way. The reason is that it is heading 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 realistic to observe such an anti-tail only when the Earth crosses the comet's orbital plane. A disc-shaped formation surrounds the celestial body from almost all sides.
The main types of comets
Types of comets can be distinguished by the time of their revolution around the Sun:
- short period comets. The orbital time of such a comet does not exceed 200 years. At the maximum distance from the Sun, they do not have tails, but only a barely perceptible coma. With a periodic approach to the main luminary, a plume appears. More than four hundred similar comets have been recorded, among which there are short-period celestial bodies with a term of revolution around the Sun of 3-10 years.
- Comets with a long orbital period. The Oort cloud, according to scientists, periodically supplies such space guests. The orbital term of these phenomena exceeds two hundred years, which makes the study of such objects more problematic. Two hundred and fifty such aliens give grounds to assert 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 activity.
The most famous comets in the solar system
There are a large number of comets that pass through the solar system. But there are the most famous cosmic bodies worth talking about.
Comet Halley
Halley's comet became famous thanks to the observations of the famous explorer, after whom it got its name. It can be attributed to short-period bodies, because its return to the main star is calculated as a period of 75 years. It is worth noting the change in this indicator towards parameters that fluctuate within 74-79 years. Its celebrity lies in the fact that this is the first celestial body of this type, the orbit of which could be calculated.
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 periodicity directly depends on the gravitational influence of large planets on the life 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 with the orbit of a comet can be observed at two points. This results in two dusty formations, which in turn form meteor showers called Aquarids and Oreanids.
If we consider the structure of such a body, then it differs little from other comets. When approaching the Sun, the formation of a sparkling plume is observed. The comet's nucleus is relatively small, which may indicate a pile of debris in the form of building material for the object's base.
It will be possible to enjoy the extraordinary spectacle of the passage of Halley's comet in the summer of 2061. A better view of the grandiose phenomenon is promised compared to the more than modest visit in 1986.
This is a fairly new discovery, which was made in July 1995. Two space explorers discovered this comet. Moreover, these scientists conducted separate searches from each other. There are many different opinions regarding the described body, but experts agree on the version that it is one of the brightest comets of the last century.
The phenomenon of this discovery lies in the fact that at the end of the 90s the comet was observed without special apparatus for ten months, which in itself cannot but surprise.
The shell of the solid core of a celestial body is rather inhomogeneous. Iced areas of unmixed gases are connected 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 the Hale-Bop comet originated within our system.
The influence of comets on the life of the planet Earth
There are many hypotheses and assumptions about this relationship. There are some comparisons that are sensational.
The Icelandic volcano Eyjafjallajokull began its active and destructive two-year activity, which surprised many scientists of that time. It happened almost immediately after the famous Emperor Bonaparte saw the comet. Perhaps this is 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 from 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 the most powerful eruption of Krakatoa volcano. All this may depend on solar activity and the activity of comets, which provoke some nuclear reactions when they approach our planet.
Comet impacts are quite rare. However, some experts believe that the Tunguska meteorite belongs to just such bodies. As arguments, they cite the following facts:
- A couple of days before the catastrophe, the appearance of dawns was observed, which, with their diversity, testified to an anomaly.
- The emergence of such a phenomenon as white nights in places unusual for it immediately after the fall of a celestial body.
- The absence of such an indicator of meteoriticity as the presence of a solid substance of this configuration.
What a comet looks like - look at the video:
The comets of the solar system are a fascinating topic and require further study. Scientists all over the world, engaged in space exploration, are trying to unravel the mysteries that these celestial bodies of amazing beauty and power carry.
A comet is a nebulous celestial object with a characteristic bright clot nucleus and luminous tail. Comets are made up mostly of frozen gases, ice, and dust. Therefore, we can say that a comet is such a huge dirty snowball flying in space around the Sun in a very elongated orbit.
Comet Lovejoy, photo taken on the ISS
Where do comets come from?
Most comets come to the Sun from two places - the Kuiper belt (the asteroid belt beyond Neptune) and the Oort cloud. The Kuiper Belt is an asteroid belt beyond the orbit of Neptune, and the Oort Cloud is a cluster of small celestial bodies at the edge of the Solar System, which is farthest from all the planets and the Kuiper Belt.
How do comets move?
Comets can spend millions of years somewhere very far from the Sun, not at all bored among their counterparts in the Oort cloud or the Kuiper belt. But one day, there, in the farthest corner of the solar system, two comets may accidentally pass next to each other or even collide. Sometimes, after such a meeting, one of the comets may begin to move towards the Sun.
The gravitational attraction of the Sun will only accelerate the movement of the comet. When it gets close enough to the Sun, the ice will start to melt and evaporate. At this point, the comet will have a tail made up of dust and gases that the comet leaves behind. Dirty snow begins to melt, turning into a beautiful "celestial tadpole" - a comet.
The fate of the comet depends on which orbit it starts its movement. As you know, all celestial bodies that have fallen into the field of attraction of the Sun can move either in a circle (which is only possible theoretically), or in an ellipse (this is how all planets, their satellites, etc. move) or in a hyperbola or parabola. Imagine a cone, and then mentally cut off a piece from it. If you cut the cone at random, you will surely get either a closed figure - an ellipse, or an open curve - a hyperbola. In order to get a circle or a parabola, it is necessary that the section plane be oriented in a strictly defined way. If the comet moves in an elliptical orbit, then this means that one day it will return to the Sun again. If the orbit of a comet becomes a parabola or hyperbola, then the attraction of our star will not be able to hold the comet, and humanity will see it only once. Having flown past the Sun, the wanderer will go away from the solar system, waving her tail in parting.
here you can see that at the very end of the shooting, the comet falls apart into several parts
It often happens that comets do not survive their journey to the Sun. If the mass of the comet is small, then it can completely evaporate in one flyby of the Sun. If the comet's material is too loose, then our star's gravity can tear the comet apart. This has happened many times. For example, in 1992, comet Shoemaker-Levy, flying past Jupiter, fell apart into more than 20 fragments. Jupiter then flew hard. The fragments of the comet crashed into the planet, causing severe atmospheric storms. More recently (November 2013), Comet ison failed its first flyby of the Sun, and its core broke up into several fragments.
How many tails does a comet have?
Comets have multiple tails. This is because comets are not only made of frozen gases and water, but also of dust. When moving towards the Sun, the comet is constantly blown by the solar wind - a stream of charged particles. It has a much stronger effect on light gas molecules than on heavy dust particles. Because of this, the comet has two tails - one dust, the other gas. The gas tail is always directed exactly from the Sun, the dust tail twists slightly along the comet's trajectory.
Sometimes comets have more than two tails. For example, a comet may have three tails, for example, if at some point a large number of dust grains are quickly released from the comet's nucleus, they form a third tail, separate from the first dust and second gas.
What happens if the Earth flies through the tail of a comet?
And nothing will happen. The tail of a comet is just gas and dust, so if the Earth flies through the comet's tail, the gas and dust will simply collide with the Earth's atmosphere and either burn up or dissolve into it. But if a comet crashes into the Earth, then we can all have a hard time.
small core comets is its only solid part, almost all of its mass is concentrated in it. Therefore, the nucleus is the root cause of the rest of the complex of cometary phenomena. Comet nuclei are still inaccessible to telescopic observations, since they are veiled by the luminous matter surrounding them, continuously flowing from the nuclei. Using high magnifications, one can look into the deeper layers of the luminous gas and dust shell, but what remains will still significantly exceed the true dimensions of the core in size. Central clump seen in the atmosphere comets visually and in photographs, is called the photometric kernel. It is believed that in the center of it is the actual nucleus comets, that is, the center of mass is located. However, as the Soviet astronomer D. O. Mokhnach showed, the center of mass may not coincide with the brightest region of the photometric nucleus. This phenomenon is called the Mokhnach effect.
The hazy atmosphere surrounding the photometric core is called coma. Coma with nucleus constitute head comets- a gaseous shell, which is formed as a result of heating of the core when approaching the Sun. Away from the Sun, the head looks symmetrical, but as it approaches it, it gradually becomes oval, then elongates even more and, on the side opposite the Sun, a tail develops from it, consisting of gas and dust included in compound heads.
The core is the most important part comets . However, there is still no consensus on what it actually is. Even in the time of Laplace, there was an opinion that the nucleus comets- a solid body consisting of easily evaporating substances such as ice or snow, quickly turning into a gas under the influence of solar heat. This classic icy model of the cometary nucleus has been significantly expanded in recent years. Whipple's model of the nucleus, a conglomerate of refractory stony particles and a frozen volatile component (methane, carbon dioxide, water, etc.), enjoys the greatest recognition. In such a core, ice layers of frozen gases alternate with dust layers. As the gases warm up, evaporating, they carry clouds of dust with them. This makes it possible to explain the formation of gas and dust tails in comets, as well as the ability of small nuclei to outgas.
According to Whipple, the mechanism for the outflow of matter from the nucleus is explained as follows. In comets that have made a small number of passages through perihelion - the so-called "young" comets - the surface protective crust has not yet had time to form, and the surface of the nucleus is covered with ice, so gas release proceeds intensively by direct evaporation. In a spectrum such comets reflected sunlight predominates, which makes it possible to spectrally distinguish the "old" comets from "young". Usually called "young" comets, which have semi-major orbital axes, as it is assumed that they first penetrate into the inner regions of the solar system. "Old" comets- This comets with a short period of revolution around the Sun, repeatedly passing their perihelion. In "old" comets, a refractory screen is formed on the surface, since during repeated returns to the Sun, the surface ice, thawing, "contaminates". This screen well protects the ice under it from exposure to sunlight.
The Whipple model explains many cometary phenomena: abundant outgassing from small nuclei, the cause of non-gravitational forces that deviate the comet from the calculated path. The streams flowing from the nucleus create reactive forces, which lead to secular accelerations or decelerations in the movement of short-period comets.
There are also other models that deny the existence of a monolithic core: one represents the core as a swarm of snowflakes, the other as an accumulation of stone and ice blocks, the third says that the core periodically condenses from the particles of a meteor swarm under the influence of planetary gravity. Whipple's model is considered the most plausible.
The masses of comet nuclei are currently determined extremely uncertainly, so we can talk about the probable range of masses: from several tons (microcomets) to several hundred, and possibly thousands of billions of tons (from 10 to 10 - 10 tons).
Coma comets surrounds the core in the form of a foggy atmosphere. For most comets, the coma consists of three main parts, which differ markedly in their physical parameters:
1) the closest region adjacent to the nucleus - internal, molecular, chemical and photochemical coma,
2) visible coma, or coma of radicals,
3) ultraviolet, or atomic coma.
At a distance of 1 a. e. from the Sun, the average diameter of the inner coma D = 10 km, visible D = 10 - 10 km and ultraviolet D = 10 km.
The most intense physical and chemical processes take place in the internal coma: chemical reactions, dissociation and ionization of neutral molecules. In a visible coma, consisting mainly of radicals (chemically active molecules) (CN, OH, NH, etc.), the process of dissociation and excitation of these molecules under the action of solar radiation continues, but less intensively than in the internal coma.
L. M. Shulman, based on the dynamic properties of matter, proposed dividing the cometary atmosphere into the following zones:
1) near-wall layer (area of evaporation and condensation of particles on the ice surface),
2) circumnuclear region (area of gas-dynamic motion of matter),
3) transition area,
4) the area of free-molecular expansion of cometary particles into interplanetary space.
But not for everyone comets the presence of all listed atmospheric regions must be mandatory.
As you get closer comets towards the Sun, the diameter of the visible head grows day by day, after passing the perihelion of its orbit, the head increases again and reaches its maximum size between the orbits of the Earth and Mars. In general, for the entire set of comets, the diameters of the heads are within wide limits: from 6000 km to 1 million km.
Comet heads in motion comets orbits take on a variety of forms. Away from the Sun, they are round, but as they approach the Sun, under the influence of solar pressure, the head takes the form of a parabola or catenary.
S. V. Orlov proposed the following classification of comet heads, taking into account their shape and internal structure:
1. Type E; - observed in comets with bright coma, framed from the side of the Sun by luminous parabolic shells, the focus of which lies in the nucleus comets.
2. Type C; - observed in comets whose heads are four times weaker than type E heads and resemble an onion in appearance.
3. Type N; - observed in comets that lack both coma and shells.
4. Type Q; - observed in comets that have a weak protrusion towards the Sun, that is, an anomalous tail.
5. Type h; - observed in comets, in the head of which uniformly expanding rings are generated - halos with a center in the nucleus.
The most impressive part comets- her tail. The tails are almost always directed away from the Sun. The tails are made up of dust, gas, and ionized particles. Therefore, depending on composition tail particles are repelled away from the Sun by forces emanating from the Sun.
F. Bessel, examining the shape of the tail comets Halley, first explained it by the action of repulsive forces emanating from the Sun. Subsequently, F. A. Bredikhin developed a more advanced mechanical theory of comet tails and proposed to divide them into three separate groups, depending on the magnitude of the repulsive acceleration.
The mechanism of the glow of cometary molecules was deciphered in 1911 by K. Schwarzschild and E. Kron, who came to the conclusion that this is the mechanism of fluorescence, that is, the re-emission of sunlight.
Sometimes rather unusual structures are observed in comets: rays emerging from the nucleus at different angles and forming a radiant tail in the aggregate; galos - systems of expanding concentric rings; contracting shells - the appearance of several shells constantly moving towards the nucleus; cloud formations; omega-shaped bends of the tails that appear when the solar wind is inhomogeneous.
Moving in orbit around the sun. The comet got its name from the Greek word for "long-haired" because people in ancient Greece believed that comets looked like stars with billowing hair.
Comets form tail only when they are close to the Sun. When are they far from sun, then comets are dark, cold, icy objects.
The icy body of a comet is referred to as core. It occupies up to 90% of the weight of the comet. The core is formed from all sorts of ice, dirt and dust that formed the foundation of the solar system about 4.6 billion years ago. At the same time, ice consists of frozen water, and a mixture of various gases, such as ammonia, carbon, methane, etc. And in the center there is a rather small stone core.
When approaching the Sun, the ice begins to heat up and evaporate, emitting gases and dust grains that form a cloud or atmosphere around the comet, called coma. As the comet continues to move closer to the Sun, the dust particles and other debris in the coma are blown away by the pressure of sunlight from the Sun. This explains the fact that comet tails are always directed away from the Sun. This process forms dust tail(it can be observed even with the naked eye). Most often, comets also have a second tail. plasma tail clearly visible in photographs, but very difficult to see without a telescope.
Over time, comets begin to move in the opposite direction from the Sun, and their activity decreases, and tails and coma disappear. They again become an ordinary ice core. And when comet orbits again lead them to the Sun, then the head and tails of the comet will appear again.
The dimensions of comets are very, very different. The smallest comets are characterized by a nucleus size of up to 16 kilometers. The largest recorded core was about 40 kilometers in diameter. Tailings of dust and ions can be colossal. ion tail Comet Hyakutake stretched for about 580 million kilometers.
There are many hypotheses about the origin of the comet, but the most popular is that comets originated from the remains of substances at birth. solar system. Some scientists believe that it was comets that brought water and organic matter to Earth, which later became the primary source of life.
Meteor Rain you can see when the Earth's orbit crosses the trail of debris left behind by the comet. From Earth every year in August you can see Perseids(meteor shower). It happens at the time when the Earth is passing through orbit of Comet Swift-Tuttle.
Astronomers do not know the exact number of comets, this is explained by the fact that the majority of them have never been seen. In 2010, just over 4,000 comets were recorded in our solar system.
Comets can change their direction of flight, which is explained by several factors: when passing near a planet, the latter may slightly change comet path; also comets moving towards the sun fall directly into it.
Over millions of years, most comets gravitationally leave the boundaries of the solar system or lose their ice and break up during movement.