solar system
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solar system- a system that consists of celestial bodies (the central luminary - the Sun and 8 major planets).
celestial bodies- these are stars, planets, asteroids, meteorites, meteors, comets, fireballs, satellites of planets and galaxies.
Stars- huge hot gaseous bodies of spherical shape. Stars are distinguished by 1. magnitude
- giant stars - stars that are larger than the sun
- dwarf stars are stars that are smaller than the sun.
- stars of the first magnitude are the brightest stars that are visible to the naked eye.
- stars of the sixth magnitude are the weakest stars in brightness, which are poorly visible to the naked eye.
planets- large celestial bodies of the solar system that move around the sun, glow with reflected sunlight. Revolve around the sun 8 planets:
- Mercury is the first planet closest to the Sun in the solar system.
- Venus is the second planet of the solar system
- Earth is the third planet of the solar system
- Mars is the fourth planet of the solar system
- Jupiter is the fifth planet in the solar system
- Saturn is the sixth planet in the solar system
- Uranus is the seventh planet in the solar system
- Neptune is the eighth planet in the solar system
Note: the planets (first, second, etc.) are counted incrementally depending on the distance from the Sun. For example, Venus is the second planet because it orbits second from the Sun.
planetary systems- groups of planets that revolve around a single star. For example:
- solar system - a planetary system that includes the Sun and the planets revolving around it. The very first system that was discovered by man.
- Upsilon Andromeda - a planetary system similar to the solar system, located in the constellation Andromeda.
meteorites- small bodies of the solar system, which are fragments of comets and asteroids. Large meteorites found in Russia:
- Tunguska - fell on June 30, 1908, in Siberia.
- Tsarevsky - fell on December 6, 1922, in the Volgograd region.
- Sikhote-Alinsky - fell on February 12, 1947, in the Ussuri taiga.
- Vitimsky - fell on September 25, 2002, in the Irkutsk region.
Meteora- very small meteorites, which are sometimes called "shooting stars".
Comets- fickle celestial bodies that appear and disappear, breaking into pieces when approaching the Sun. The most famous is Halley's Comet. The first time appeared in ancient times - in 239 BC.
satellites planets - small celestial bodies that revolve around a larger planet.
For example: the planet earth has 1 satellite - the moon
- Mars - 2 satellites - Deimos and Phobos
- Jupiter - 63
- Saturn - 62
- Uranus - 27
- Neptune - 13
Universe- all galaxies that form a huge endless space.
Used Books:
1. Student's handbook for primary school: mathematics, Russian language, the world around / N.A. Abelskaya, M.B. Eliseeva, N.M. Kupchinsky, N.N. Mashkova. - M.: AST; SPb.: Owl, 2010 2. A complete reference book for elementary school students. 1-4 grade. Maths. Russian language. The world. Literary reading/ A.A. Biryukova, E.I. Sinitsina. - M.: AST: SLOVO, 2010. 3. Natural history. Grade 5: textbook for educational institutions/ V.M. Pakulova, N.V. Ivanova. - M.: Bustard, 2007. 4. Big Encyclopedia Cyril and Methodius. Electronic allowance. 2009.
Used Internet resources:
Wikipedia - the free encyclopedia
Links Wikipedia. planetary system http://ru.wikipedia.org/wiki/%D0%9F%D0%BB%D0%B0%D0%BD%D0%B5%D1%82%D0%B0%D1%80%D0%BD%D0 %B0%D1%8F_%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC%D0%B0 Wikipedia. Upsilon Andromeda
The universe consists of a huge number of cosmic bodies. Every night we can contemplate the stars in the sky, which seem very small, although they are not. In fact, some of them are many times larger than the Sun. It is assumed that a planetary system is formed around each lone star. So, for example, the solar system was formed near the Sun, consisting of eight large, as well as small and comets, black holes, cosmic dust, etc.
The Earth is a cosmic body because it is a planet, a spherical object that reflects sunlight. Seven other planets are also visible to us only due to the fact that they reflect the light of the star. In addition to Mercury, Venus, Mars, Uranus, Neptune and Pluto, which was also considered a planet until 2006, a huge number of asteroids, which are also called minor planets, are also concentrated in the solar system. Their number reaches 400 thousand, but many scientists agree that there are more than a billion of them.
Comets are also cosmic bodies moving along elongated trajectories and approaching in certain time to the sun. They consist of gas, plasma and dust; overgrown with ice, reach a size of tens of kilometers. When approaching a star, comets gradually melt. From high temperature the ice evaporates, forming a head and a tail that reaches astonishing proportions.
Asteroids are the cosmic bodies of the solar system, also called minor planets. Their main part is concentrated between Mars and Jupiter. They consist of iron and stone and are divided into two types: light and dark. The first ones are lighter, the second ones are harder. Asteroids are irregular in shape. It is assumed that they were formed from the remnants of cosmic matter after the formation of the main planets, or they are fragments of a planet located between Mars and Jupiter.
Some cosmic bodies reach the Earth, but, passing through the thick layers of the atmosphere, they heat up during friction and break into small pieces. Therefore, relatively small meteorites fell on our planet. This phenomenon is by no means uncommon; fragments of asteroids are kept in many museums around the world, they were found in 3500 places.
There are not only large objects in space, but also tiny ones. So, for example, bodies up to 10 m in size are called meteoroids. Cosmic dust is even smaller, up to 100 microns in size. It appears in the atmospheres of stars as a result of gas emissions or explosions. Not all space bodies have been studied by scientists. These include black holes, which are found in almost every galaxy. They cannot be seen, it is only possible to determine their location. Black holes have a very strong attraction, so they do not even let go of light. They annually absorb huge volumes of hot gas.
space bodies have different forms, dimensions, location in relation to the Sun. Some of them are combined into separate groups to make it easier to classify them. So, for example, asteroids located between the Kuiper belt and Jupiter are called Centaurs. Vulcanoids are thought to lie between the Sun and Mercury, although no object has yet been discovered.
PLAN
Introduction
1. Asteroids
2. Meteorites
3. Small fragments
5. Search for planets in the solar system
Literature
Introduction
In the solar system, in addition to the large planets and their satellites, many so-called small bodies move: asteroids, comets and meteorites. Small bodies of the solar system range in size from hundreds of microns to hundreds of kilometers.
Asteroids. From the point of view of physics, asteroids or, as they are also called, small planets, are dense and durable bodies. According to their composition and properties, they can be divided into three groups: stone, iron-stone and iron. The asteroid is a cold body. But it, like the Moon, for example, reflects sunlight, and therefore we can observe it as a star-shaped object. This is where the name "asteroid" comes from, which in Greek means star-shaped. Since asteroids move around the Sun, their position in relation to the stars is constantly and rather rapidly changing. It is on this initial sign that observers discover asteroids.
Comets, or "tailed stars", have been known since time immemorial. Comet is complicated physical phenomenon, which can be briefly described using several concepts. The nucleus of a comet is a mixture or, as they say, a conglomerate of dust particles, water ice and frozen gases. The ratio of dust to gas in cometary nuclei is approximately 1:3. The sizes of cometary nuclei, according to scientists, are in the range from 1 to 100 km. The possibility of the existence of both smaller and larger nuclei is now being discussed. Known short-period comets have nuclei ranging in size from 2 to 10 km. The size of the nucleus of the brightest comet Haley-Bopp, which was observed with the naked eye in 1996, is estimated at 40 km.
A meteoroid is a small body that revolves around the sun. A meteor is a meteoroid that flew into the atmosphere of the planet and became red-hot to a shine. And if its remnant fell to the surface of the planet, it is called a meteorite. A meteorite is considered "fallen" if there are eyewitnesses who observed its flight in the atmosphere; otherwise, it is called "found".
Let us consider the above mentioned small bodies of the solar system in more detail.
1. asteroids
These cosmic bodies differ from the planets primarily in their size. So, the largest of the small planets, Ceres, has a diameter of 995 km; next after it (in size): Palada - 560 km, Hygea - 380 km, Psyche - 240 km, etc. For comparison, we can point out that the smallest of the major planets Mercury has a diameter of 4878 km, i.e. 5 times greater than the diameter of Ceres, and their masses differ by many hundreds of times.
Total number minor planets available for observation modern telescopes, is determined at 40 thousand, but their total mass is 1 thousand times less than the mass of the Earth.
The movement of small planets around the Sun occurs in elliptical orbits, but more elongated (the average eccentricity of their orbits is 0.51) than that of the large planets, and the inclination of the orbital planes to the ecliptic is greater than that of the large planets (the average angle is 9.54) . Most of the planets revolve around the Sun between the orbits of Mars and Jupiter, forming the so-called asteroid belt. But there are also small planets whose orbits are closer to the Sun than the orbit of Mercury. The most distant are beyond Jupiter and even beyond Saturn.
Space researchers express various ideas about the reason for the large concentration of asteroids in the relatively narrow space of the interplanetary medium between the orbits of Mars and Jupiter. One of the most common hypotheses of the origin of the bodies of the asteroid belt is the idea of the destruction of the mythical planet Phaeton. The very idea of the existence of the planet is supported by many scientists and even seems to be backed up by mathematical calculations. However, the reason for the destruction of the planet remains unexplained. Various assumptions are made. Some researchers believe that the destruction of Phaeton occurred as a result of its collision with some large body. According to others, the reasons for the collapse of the planet were explosive processes in its depths. At present, the problem of the origin of the bodies of the asteroid belt is included in the extensive program of space exploration at the international and national levels.
Among the minor planets, a peculiar group of bodies stands out, the orbits of which intersect with the Earth's orbit, and therefore, there is a potential possibility of their collision with it. The planets of this group became known as Apollo objects, or simply Apollo (Wetherill, 1979). For the first time, the existence of Apollo has become known since the 30s of this century. In 1932, an asteroid was discovered. They called him
Apollo 1932 H.A. But he did not arouse much interest, although his name has become a household name for all asteroids crossing the earth's orbit.
In 1937, a cosmic body with a diameter of approximately 1 km passed 800,000 km from the Earth and twice the distance from the Moon. Subsequently, he was named Hermes. To date, 31 such bodies have been identified, and each of them has received its own name. The sizes of their diameters vary from 1 to 8 km, and the inclination of the orbital planes to the ecliptic ranges from 1 to 68. Five of them rotate in orbits between the Earth and Mars, and the remaining 26 - between Mars and Jupiter (Wetherill, 1979). It is believed that out of 40 thousand minor planets of the asteroid belt with a diameter of more than 1 km, there may be several hundred Apollos. Therefore, the collision of such celestial bodies with the Earth is quite probable, but after very long time intervals.
It can be assumed that once a century one of these cosmic bodies can pass near the Earth at a distance less than from us to the Moon, and once in 250 thousand years it can collide with our planet. The impact of such a body releases energy equal to 10 thousand hydrogen bombs each with a capacity of 10 Mt. This should form a crater with a diameter of about 20 km. But such cases are rare and human history unknown. Hermes belongs to class III asteroids, and there are many such bodies and more large size- II and I classes. The impact when they collide with the Earth, of course, will be even more significant.
When Uranus was discovered in 1781, its average heliocentric distance turned out to correspond to the Titius-Bode rule, then from 1789 the search for a planet began, which, according to this rule, should have been located between the orbits of Mars and Jupiter, at an average distance a = 2, 8 a.u. from the sun. But scattered surveys of the sky did not bring success, and therefore on September 21, 1800, several German astronomers, led by K. Zach, decided to organize a collective search. They divided the entire search for the zodiac constellations into 24 sections and distributed among themselves for thorough research. But before they had time to enter the systematic search, as on January 1, 1871. the Italian astronomer G. Piacii (1746-1826) discovered the star-shaped object of the seventh magnitude, slowly moving through the constellation Taurus. The orbit of the object calculated by K. Gaus (1777-1855) turned out to be a planet corresponding to the Titius-Bode rule: semi-major axis a = 2.77 AU. and eccentricity e=0.080. Piatia named the newly discovered planet Ceres.
On March 28, 1802, the German physician and astronomer W. Olbers (1758-1840) discovered another planet (8m) near Ceres, called Pallas (a=2.77 AU, e=0.235). On September 2, 1804, the third planet, Juno (a = 2.67 AU), was discovered, and on March 29, 1807, 4, Vesta (a = 2.36 AU). Everything again discovered planets had a star-shaped appearance, without disks, indicating their small geometric dimensions. Therefore, these celestial bodies were called minor planets or, at the suggestion of V. Herschel, asteroids (from the Greek "aster" - stellar and "eidos" - view).
By 1891, about 320 asteroids had been discovered by visual methods. At the end of 1891, the German astronomer M. Wolf (1863-1932) proposed a photographic search method: with a 2-3-hour exposure, the images of stars on the photographic plate turned out to be dotted, and the trail of a moving asteroid was in the form of a small dash. Photographic techniques have led to a dramatic increase in asteroid discoveries. Particularly intensive studies of minor planets are now being carried out at the Institute of Theoretical Astronomy (in St. Petersburg) and at the Crimean Astrophysical Observatory of the Russian Academy of Sciences.
Asteroids whose orbits are reliably determined are assigned a name and a serial number. More than 3500 such asteroids are now known, but there are much more in the solar system.
Of the indicated number of known asteroids, astronomers of the Crimean Astrophysical Observatory discovered about 550, perpetuating the names of famous people in their names.
The vast majority (up to 98%) of known asteroids move between the orbits of Mars and Jupiter, at average distances from the Sun from 2.06 to 4.30 AU. (circulation periods from 2.96 to 8.92 years). However, there are asteroids with unique orbits, and they are given masculine names, usually from Greek mythology.
The first three of these minor planets move outside the asteroid belt, and at perihelion Icarus approaches the Sun twice as close to Mercury, and Hermes and Adonis - closer to Venus. They can approach the Earth at a distance of 6 million to 23 million km, and Hermes in 1937 passed close to the Earth even at a distance of 580 thousand km, i.e. only one and a half times farther than the moon. Hidalgo at aphelion goes beyond the orbit of Saturn. But Hidalgo is no exception. Per last years about 10 asteroids have been discovered, the perihelions of which are located near the orbits of the planets terrestrial group, and aphelia - near the orbits of Jupiter. Such orbits are characteristic of comets of the Jupiter family and indicate a possible common origin of asteroids and comets.
In 1977, a unique asteroid was discovered that revolves around the Sun in an orbit with a semi-major axis a = 13.70 AU. and eccentricity e = 0.38, so that at perihelion (q = 8.49 AU) it enters the orbit of Saturn, and at aphelion (Q = 18.91 AU) it approaches the orbit of Uranus. He is named Chiron. Apparently, there are other similar distant asteroids, the search for which continues.
The brightness of most known asteroids during the opposition is from 7 m to 16 m , but there are also fainter objects. The brightest (up to 6 m) is Vesta.
The widths of asteroids are calculated from their brightness and reflectivity in visual and infrared rays. It turned out that there are not so many large asteroids. The largest are Ceres (diameter 1000 km), Pallas (610 km), Vesta (540 km) and Hygia (450 km). Only 14 asteroids have diameters greater than 250 km, while the rest have smaller diameters, up to 0.7 km. Bodies of such small sizes cannot have a spheroidal shape, and all asteroids (except, perhaps, the largest ones) are shapeless blocks.
The masses of asteroids are extremely different: the largest, close to 1.5 . 10 21 kg (i.e. 4 thousand times less than the mass of the earth), Ceres has. The total mass of all asteroids does not exceed 0.001 Earth masses. Of course, all these celestial bodies are devoid of an atmosphere. Axial rotation has been found in many asteroids by regular changes in their brightness.
In particular, the period of rotation of Ceres is 9.1 hours, and Pallas - 7.9 hours.
Icarus rotates fastest of all, in 2 h 16 m.
The study of the reflectivity of many asteroids made it possible to combine them into three main groups: dark, light and metallic. The surface of dark asteroids reflects only up to 5% of the sunlight falling on it and consists of substances similar to black basalt and carbonaceous rocks. These asteroids are often referred to as carbonaceous. Light asteroids reflect from 10% to 25% of sunlight, which makes their surface similar to silicon compounds - these are stone asteroids. Metallic asteroids (their absolute minority) are also light, but in their reflective properties, their surface is similar to iron-nickel alloys. Such a subdivision of asteroids is also confirmed by the chemical composition of meteorites falling to Earth. A small number of studied asteroids do not belong to any of the three main groups.
It is significant that in the spectra of carbonaceous asteroids, a water absorption band (l = 3 μm) was found. In particular, the surface of the asteroid Ceres is composed of minerals similar to terrestrial clays and containing about 10% water.
With small sizes and masses of asteroids, the pressure in their interiors is low: even for the largest asteroids, it does not exceed 7 10 5
8 10 5 GPa (700 - 800 atm) and cannot cause heating of their solid cold bowels. Only the surface of asteroids is very weakly heated by the Sun far from them, but even this insignificant energy is radiated into interplanetary space. The surface temperature of the vast majority of asteroids calculated according to the laws of physics turned out to be close to 150 - 170 K (-120...-100°C).
And only a few asteroids that pass near the Sun, the surface during such periods is very hot. Thus, the surface temperature of Icarus rises to almost 1000 K (+730°C), and as it moves away from the Sun, it drops sharply again.
The orbits of the remaining asteroids are subject to significant perturbations from the gravitational influence of the major planets, mainly Jupiter. Especially strong perturbations are experienced by small asteroids, which leads to collisions of these bodies and their fragmentation into falcons of the most diverse sizes, from hundreds of meters across to dust particles.
Currently, the physical nature of asteroids is being studied, because it can be used to trace the evolution (development) of the substance from which the solar system was formed.
2. meteorites
A variety of meteoroids (cosmic fragments of large asteroids and comets) move in near-Earth outer space. Their speeds range from 11 to 72 km/s. It often happens that the paths of their movement intersect with the Earth's orbit and they fly into its atmosphere.
Meteorites - stone or iron bodies falling to Earth from interplanetary space. The fall of meteorites to Earth is accompanied by sound, light and mechanical phenomena. A bright fireball called a bolide sweeps across the sky, accompanied by a tail and flying sparks. After the car disappears, after a few seconds, explosion-like impacts called shock waves are heard, which sometimes cause significant shaking of the ground and buildings.
The phenomena of the invasion of cosmic bodies into the atmosphere have three main stages:
1. Flight in a rarefied atmosphere (up to altitudes of about 80 km), where the interaction of air molecules is carpuscular in nature. Air particles collide with the body, stick to it or are reflected and transfer part of their energy to it. The body heats up from the continuous bombardment of air molecules, but does not experience noticeable resistance, and its speed remains almost unchanged. At this stage, however, the outer part of the cosmic body heats up to a thousand degrees and more. Here, the characteristic parameter of the problem is the ratio of the free path to the size of the body L, which is called the Knudsen number K n . In aerodynamics, it is customary to take into account the molecular approach to air resistance at K n >0.1.
2. Flight in the atmosphere in the mode of continuous air flow around the body, that is, when the air is considered continuous medium and the atomic-molecular character of its composition is not explicitly taken into account. At this stage, a head shock wave appears in front of the body, followed by a sharp increase in pressure and temperature. The body itself is heated due to convective heat transfer, as well as due to radiation heating. The temperature can reach several tens of thousands of degrees, and the pressure can reach hundreds of atmospheres. When braking hard, there are significant overloads. There are deformations of bodies, melting and evaporation of their surfaces, mass entrainment by an oncoming air flow (ablation).
3. When approaching the Earth's surface, the air density increases, the resistance of the body increases, and it either practically stops at some height, or continues its path until a direct collision with the Earth. In this case, often large bodies are divided into several parts, each of which falls separately to the Earth. With strong deceleration of the cosmic mass above the Earth, the shock waves accompanying it continue their movement to the Earth's surface, are reflected from it and produce disturbances in the lower layers of the atmosphere, as well as the Earth's surface.
The process of falling of each meteoroid is individual. No opportunity in short story describe all the possible features of this process.
There are much more “found” meteorites than “fallen” meteorites. Often they are found by tourists or peasants working in the field. Since meteorites are dark in color and easily visible in the snow, the Antarctic ice fields, where thousands of meteorites have already been found, are an excellent place to look for them. For the first time, a meteorite in Antarctica was discovered in 1969 by a group of Japanese geologists who studied glaciers. They found 9 fragments lying side by side, but related to four different types meteorites. It turned out that meteorites that fell on the ice in different places gather where the ice fields moving at a speed of several meters per year stop, resting on mountain ranges. The wind destroys and dries the upper layers of ice (dry sublimation occurs - ablation), and meteorites concentrate on the surface of the glacier. Such ice has a bluish color and is easily distinguishable from the air, which is what scientists use when studying places promising for collecting meteorites.
An important meteorite fall occurred in 1969 in Chihuahua (Mexico). The first of many large fragments was found near a house in the village of Pueblito de Allende, and, following tradition, all found fragments of this meteorite were united under the name Allende. The fall of the Allende meteorite coincided with the beginning lunar program Apollo and gave scientists the opportunity to work out methods for analyzing extraterrestrial samples. In recent years, some meteorites containing white fragments embedded in darker parent rock have been found to be lunar fragments.
The Allende meteorite belongs to chondrites, an important subgroup of stony meteorites. They are called so because they contain chondrules (from the Greek chondros, seed) - the oldest spherical particles that condensed in a protoplanetary nebula and then became part of later rocks. Such meteorites make it possible to estimate the age of the solar system and its initial composition. The inclusions of the Allende meteorite rich in calcium and aluminum, which were the first to condense due to their high boiling point, have an age measured from radioactive decay of 4.559 ± 0.004 billion years. This is the most accurate estimate of the age of the solar system. In addition, all meteorites carry "historical records" caused by the long-term influence of galactic cosmic rays, solar radiation and solar wind on them. By examining the damage caused by cosmic rays, we can tell how long the meteorite stayed in orbit before it fell under the protection of the earth's atmosphere.
A direct relationship between meteorites and the Sun follows from the fact that the elemental composition of the oldest meteorites - chondrites - exactly repeats the composition of the solar photosphere. The only elements whose content differs are volatiles, such as hydrogen and helium, which evaporated abundantly from meteorites during their cooling, as well as lithium, which was partially “burned out” on the Sun in nuclear reactions. The terms "solar composition" and "chondrite composition" are used interchangeably when describing the "recipe for solar matter" mentioned above. Stone meteorites, the composition of which differs from the sun, are called achondrites.
3. Small shards.
The near-solar space is filled with small particles, the sources of which are the collapsing nuclei of comets and collisions of bodies, mainly in the asteroid belt. The smallest particles gradually approach the Sun as a result of the Poynting-Robertson effect (it consists in the fact that the pressure of sunlight on a moving particle is not directed exactly along the Sun-particle line, but as a result of light aberration it is deflected back and therefore slows down the movement of the particle). The fall of small particles on the Sun is compensated by their constant reproduction, so that in the plane of the ecliptic there is always an accumulation of dust that scatters the sun's rays. On the darkest nights it is visible as zodiacal light, stretching in a wide band along the ecliptic in the west after sunset and in the east before sunrise. Near the Sun, zodiacal light passes into a false corona ( F-crown, from false - false), which is visible only when total eclipse. With an increase in the angular distance from the Sun, the brightness of the zodiacal light rapidly decreases, but at the antisolar point of the ecliptic it increases again, forming a counterradiance; this is due to the fact that small dust particles intensively reflect light back.
From time to time, meteoroids enter the Earth's atmosphere. The speed of their movement is so high (on average 40 km/s) that almost all of them, except for the smallest and largest ones, burn out at an altitude of about 110 km, leaving long luminous tails - meteors, or shooting stars. Many meteoroids are associated with the orbits of individual comets, so meteors are observed more often when the Earth passes near such orbits at certain times of the year. For example, there are many meteors around August 12 each year as the Earth crosses the Perseid shower associated with particles lost by comet 1862 III. Another stream, the Orionids, around October 20 is associated with dust from Halley's comet.
Particles smaller than 30 microns can slow down in the atmosphere and fall to the ground without being burned; such micrometeorites are collected for laboratory analysis. If particles of a few centimeters or more in size consist of a sufficiently dense substance, then they also do not burn out completely and fall to the Earth's surface in the form of meteorites. More than 90% of them are stone; only a specialist can distinguish them from terrestrial rocks. The remaining 10% of meteorites are iron (in fact, they are composed of an alloy of iron and nickel).
Meteorites are considered fragments of asteroids. Iron meteorites were once in the composition of the nuclei of these bodies, destroyed by collisions. It is possible that some loose and volatile meteorites originated from comets, but this is unlikely; most likely, large particles of comets burn up in the atmosphere, and only small ones remain. Considering how difficult it is for comets and asteroids to reach the Earth, it is clear how useful it is to study meteorites that independently "arrived" on our planet from the depths of the solar system.
4. Comets
Comets are the most efficient celestial bodies in the solar system. Comets are a kind of cosmic icebergs, consisting of frozen gases, complex chemical composition, water ice and refractory mineral matter in the form of dust and larger fragments.
Although comets, like asteroids, move around the Sun in conical curves, they look strikingly different from asteroids. If asteroids shine by reflected sunlight and in the field of view of a telescope resemble slowly moving faint stars, then comets scatter sunlight intensively in some of the most characteristic regions of the spectrum for comets, and therefore many comets are visible naked eye, although the diameters of their cores rarely exceed 1–5 km.
Comets are of interest to many scientists: astronomers, physicists, chemists, biologists, gas dynamics, historians, etc. And this is natural. After all, comets suggested to scientists that the solar wind blows in interplanetary space; Perhaps comets are the "culprits" of the emergence of life on Earth, since they could bring complex organic compounds into the Earth's atmosphere. In addition, comets, apparently, carry valuable information about the initial stages of the protoplanetary cloud, from which the Sun and planets also formed.
At the first acquaintance with a bright comet, it may seem that the tail is the most important part of the comet. But if in the etymology of the word "comet" the tail appeared main reason for such a name, then from a physical point of view, the tail is a secondary formation, developed from a rather tiny nucleus, the most important part of the comet as a physical object. Comet nuclei are the primary cause of the rest of the complex of cometary phenomena, which are still not accessible 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 gas-dust shell glowing around the nucleus, but what remains will still significantly exceed the true dimensions of the nucleus in size. The central cluster, visible in the diffuse atmosphere of a comet visually and in photographs, is called the photometric nucleus. It is believed that in its center is the comet's own nucleus, i.e. the comet's center of mass is located.
The foggy atmosphere surrounding the photometric core and gradually fading away, merging with the sky background, is called a coma. The coma together with the nucleus make up the head of the comet. Away from the Sun, the head looks symmetrical, but as it approaches the Sun, it gradually becomes oval, then the head lengthens even more, and a tail develops from it on the side opposite the Sun.
So, the nucleus is the most important part of a comet. However, there is still no consensus on what it really is. Even in the time of Bessel and Laplace, there was an idea of the comet's nucleus as a solid body, consisting of easily evaporating substances such as ice or snow, which quickly pass into the gas phase under the influence of solar heat. This icy classical model of the cometary nucleus has been significantly expanded and developed in recent times. The model of the nucleus developed by Whipple, a conglomerate of refractory stony particles and a frozen volatile component (CH4, CO2, H2O, etc.), enjoys the greatest recognition among comet researchers. In such a core, ice layers of frozen gases alternate with dust layers. As the solar heat warms, gases like evaporating "dry ice" break through, dragging clouds of dust with them. This makes it possible, for example, to explain the formation of gas and dust tails in comets, as well as the ability of small nuclei of comets to actively release gases.
Comet heads take on a variety of shapes as comets orbit. Away from the SUN, the heads of comets are round, which is explained by the weak effect of solar radiation on the particles of the head, and its outlines are determined by the isotropic expansion of cometary gas into interplanetary space. These are tailless comets appearance resembling globular star clusters. Approaching the Sun, the comet's head takes the form of a parabola or catenary. The parabolic shape of the head is explained by the "fountain" mechanism. The formation of heads in the form of a catenary is associated with the plasma nature of the cometary atmosphere and the impact of the solar wind on it and with the magnetic field carried by it.
Sometimes the comet's head is so small that the comet's tail appears to emerge directly from the nucleus. In addition to changing the outlines, various structural formations appear and disappear in the heads of comets: tacks, shells, rays, outpourings from the nucleus, etc.
Large comets with tails stretching far across the sky have been observed since ancient times. Comets were once thought to be atmospheric phenomena. This misconception was refuted by Brahe, who found that the comet of 1577 occupied the same position among the stars when observed from different points, and, therefore, is farther from us than the Moon.
The movement of comets across the sky was first explained by Halley (1705), who found that their orbits were close to parabolas. He determined the orbits of 24 bright comets, and it turned out that the comets of 1531 and 1682. have very similar orbits. From this, Halley concluded that this is the same comet that moves around the Sun in a very elongated ellipse with a period of about 76 years. Halley predicted that it would reappear in 1758, and in December 1758 it was indeed discovered. Halley himself did not live to see this time and could not see how brilliantly his prediction was confirmed. This comet (one of the brightest) was named Halley's comet.
Comets are named after the names of the people who discovered them. In addition, a newly discovered comet is assigned a provisional designation based on the year of discovery, with the addition of a letter indicating the sequence in which the comet passes through perihelion in that year.
Only a small part of the comets observed annually are periodic, i.e. known for their previous appearances. Most comets move in very elongated ellipses, almost parabolas. Their periods of revolution are not exactly known, but there is reason to believe that they reach many millions of years. Such comets move away from the Sun at distances comparable to interstellar ones. The planes of their almost parabolic orbits do not concentrate to the plane of the ecliptic and are randomly distributed in space. forward direction movement is as common as the reverse.
Periodic comets move in less elongated elliptical orbits and have very different characteristics. Of the 40 comets observed more than once, 35 have orbits inclined by less than 45° to the plane of the ecliptic. Only Halley's comet has an orbit with an inclination greater than 90° and therefore moves in reverse direction. Among the short-period (i.e., having periods of 3 - 10 years) comets, the "Jupiter family" stands out - a large group of comets, the aphelia of which are at the same distance from the Sun as the orbit of Jupiter. It is assumed that the "family of Jupiter" was formed as a result of the capture of comets by the planet, which previously moved in more elongated orbits. Depending on the relative position Jupiter and comets, the eccentricity of the comet's orbit can both increase and decrease. In the first case, there is an increase in the period or even a transition to a hyperbolic orbit and the loss of the comet by the Solar System, in the second, a decrease in the period.
The orbits of periodic comets are subject to very noticeable changes. Sometimes a comet passes near the Earth several times, and then, by the attraction of the giant planets, it is thrown into a more distant orbit and becomes unobservable. In other cases, on the contrary, a comet that has never been observed before becomes visible due to the fact that it passed near Jupiter or Saturn and changed its orbit dramatically. In addition to such abrupt changes, known only for a limited number of objects, the orbits of all comets experience gradual changes.
Orbital changes are not the only possible reason for the disappearance of comets. It has been reliably established that comets are rapidly destroyed. The brightness of short-period comets weakens with time, and in some cases the destruction process was observed almost directly. Bielly's comet is a classic example. It was discovered in 1772 and observed in 1813, 1826 and 1832. In 1845, the size of the comet was increased, and in January 1846. observers were surprised to find two very close comets instead of one. The relative motions of both comets were calculated, and it turned out that Bieli's comet had split into two about a year ago, but at first the components were projected one on top of the other, and the separation was not immediately noticed. Comet Bieli was observed once more, with one component much weaker than the other, and it was not possible to find it again. On the other hand, a meteor shower was repeatedly observed, the orbit of which coincided with the orbit of Biel's comet.
When solving the question of the origin of comets, one cannot do without knowing the chemical composition of the substance from which the cometary nucleus is composed. It would seem, what could be easier? We need to photograph more spectra of comets, decipher them - and the chemical composition of cometary nuclei will immediately become known to us. However, the matter is not as simple as it seems at first glance. The spectrum of the photometric nucleus can simply be the reflected solar or molecular emission spectrum. The reflected solar spectrum is continuous and tells nothing about chemical composition the area from which it was reflected - the core or the dusty atmosphere surrounding the core. The emission gas spectrum carries information about the chemical composition of the gaseous atmosphere surrounding the nucleus, and also does not tell us anything about the chemical composition of the surface layer of the nucleus, since molecules emitting in the visible region, such as C2, CN, CH, MH, OH, etc., are secondary, daughter molecules - "fragments" of more complex molecules or molecular complexes that make up the cometary nucleus. These complex parent molecules, evaporating into the circumnuclear space, are quickly exposed to the destructive action of the solar wind and photons, or decay or dissociate into simpler molecules, the emission spectra of which can be observed from comets. The parent molecules themselves give a continuous spectrum.
The first to observe and describe the spectrum of the comet's head was the Italian Donati. Against the background of the faint continuous spectrum of comet 1864, he saw three broad luminous bands: blue, green and yellow color. As it turned out, this confluence belonged to C2 carbon molecules, which found themselves in abundance in the cometary atmosphere. These emission bands of C2 molecules are called Swan bands, after the scientist who studied the spectrum of carbon. First slit spectrogram of the head Big Comet 1881 was obtained by the Englishman Heggins, who discovered in the spectrum the radiation of the reactive cyanide radical CN.
Away from the Sun, at a distance of 11 AU, the approaching comet looks like a small hazy speck, sometimes with signs of the beginning formation of a tail. The spectrum obtained from a comet located at such a distance, and up to a distance of 3-4 AU, is continuous, because at such large distances, the emission spectrum is not excited due to weak photon and corpuscular solar radiation.
This spectrum is formed as a result of the reflection of sunlight from dust particles or as a result of its scattering on polyatomic molecules or molecular complexes. At a distance of about 3 AU from the Sun, i.e. when the cometary nucleus crosses the asteroid belt, the first emission band of the cyanide molecule appears in the spectrum, which is observed in almost the entire head of the comet. At a distance of 2 AU radiations of triatomic C3 and NH3 molecules are already excited, which are observed in a more limited region of the comet's head near the nucleus than all the increasing radiations of CN. At a distance of 1.8 AU carbon emissions appear - Swan bands, which immediately become noticeable in the entire head of the comet: both near the nucleus and at the boundaries of the visible head.
The mechanism of the glow of cometary molecules was deciphered as early as 1911. K. Schwarzschild and E. Kron, who, studying the emission spectra of Halley's comet (1910), came to the conclusion that the molecules of cometary atmospheres resonantly re-emit sunlight. This glow is similar to the resonant glow of sodium vapor in the well-known experiments of Aud, who was the first to notice that when illuminated with light having the frequency of a yellow sodium doublet, sodium vapor itself begins to glow at the same frequency with a characteristic yellow light. This is the resonant fluorescence mechanism, which is a frequent case of the more general luminescence mechanism. Everyone knows the glow of fluorescent lamps above shop windows, in fluorescent lamps, etc. A similar mechanism causes the gases in comets to glow.
To explain the glow of the green and red oxygen lines (similar lines are also observed in the spectra of auroras), various mechanisms were invoked: electron impact, dissociative recombination, and photodissociation. Electron impact, however, fails to explain the higher intensity of the green line in some comets compared to the red line. Therefore, more preference is given to the photodissociation mechanism, which is supported by the brightness distribution in the comet's head. However, this issue has not yet been finally resolved, and the search for the true mechanism of the glow of atoms in comets continues. Until now, the question of the parent, primary molecules that make up the cometary nucleus remains unresolved, and this issue is very important, since it is the chemistry of the nuclei that predetermines the unusually high activity of comets, capable of developing giant atmospheres and tails from very small nuclei, exceeding in size all in size famous bodies in the solar system.
5. Search for planets in the solar system.
More than once, assumptions have been made about the possibility of the existence of a planet closer to the Sun than Mercury. Le Verrier (1811–1877), who predicted the discovery of Neptune, investigated anomalies in the movement of the perihelion of Mercury's orbit and, on the basis of this, predicted the existence of a new unknown planet inside its orbit. Soon there was a message about her observation and the planet was even given a name - Vulcan. But the discovery was not confirmed.
In 1977, the American astronomer Cowell discovered a very faint object, which was dubbed the "tenth planet". But the object turned out to be too small for the planet (about 200 km). It was named Chiron and attributed to the asteroids, among which it was then the most distant: the aphelion of its orbit was removed by 18.9 AU. and almost touches the orbit of Uranus, and the perihelion lies just beyond the orbit of Saturn at a distance of 8.5 AU. from the sun. With an orbital inclination of just 7°, it can indeed come close to Saturn and Uranus. Calculations show that such an orbit is unstable: Chiron will either collide with the planet or be ejected from the solar system.
From time to time, theoretical predictions about the existence of large planets beyond the orbit of Pluto are published, but so far they have not been confirmed. Analysis of cometary orbits shows that up to a distance of 75 AU. planets larger than the earth beyond Pluto. However, the existence of a large number of small planets in this area is quite possible, which are not easy to detect. The existence of this cluster of non-Neptunian bodies has long been suspected and even received the name - the Kuiper belt, after the famous American planetary explorer. However, it was only recently that the first objects were found in it. In 1992–1994, 17 minor planets were discovered beyond the orbit of Neptune. Of these, 8 move at distances of 40–45 AU. from the Sun, i.e. even beyond the orbit of Pluto.
Due to their great distance, the brightness of these objects is extremely weak; only the largest telescopes in the world are suitable for their search. Therefore, only about 3 square degrees have been systematically viewed so far. celestial sphere, i.e. 0.01% of its area. Therefore, it is expected that beyond the orbit of Neptune there may be tens of thousands of objects similar to those discovered, and millions of smaller ones, with a diameter of 5–10 km. Judging by estimates, this cluster of small bodies is hundreds of times more massive than the asteroid belt located between Jupiter and Mars, but inferior in mass to the giant cometary Oort cloud.
Objects beyond Neptune are still difficult to attribute to any class of small bodies in the solar system - to asteroids or comet nuclei. The newly discovered bodies are 100–200 km in size and have a rather red surface, indicating its ancient composition and the possible presence of organic compounds. Bodies of the "Kuiper belt" have recently been discovered quite often (by the end of 1999, about 200 of them had been discovered). Some planetary scientists believe that it would be more correct to call Pluto not "the smallest planet", but "the largest body of the Kuiper belt."
Literature
1. V.A. Brastein "Planets and their observation" Moscow "Nauka" 1979.
2. S. Dole “Planets for people” Moscow “Science” 1974.
3. K.I. Churyumov "Comets and their observation" Moscow "Nauka" 1980.
4. E.L. Krinov "Iron Rain" Moscow "Science" 1981.
5. K.A. Kulikov, N.S. Sidorenkov "Planet Earth" Moscow "Science"
6. B.A. Vorontsov - Velyaminov “Essays on the Universe” Moscow “Science”
7. N.P. Erpyleev "Encyclopedic Dictionary of a Young Astronomer" Moscow "Pedagogy" 1986.
8. E.P. Levitan “Astronomy” Moscow “Enlightenment” 1994
