How many comets are there in the solar system. Solar system. Comets. Heavenly Wanderers
solar system. Comets. Heavenly Wanderers
Besides major planets Comets and asteroids move around the Sun. Comets are the longest objects in the solar system. The word “comet” translated from Greek means “hairy”, “long-haired”. As the comet approaches the Sun, it takes on a spectacular appearance, heating up under the influence of the sun's heat so that gas and dust fly away from the surface, forming a bright tail. The appearance of most comets is unpredictable. People have been paying attention to them since time immemorial. It is impossible not to notice in the sky a spectacle so rare, and therefore terrifying, more terrible than any eclipse, when a foggy body is visible in the sky, sometimes so bright that it can sparkle through the clouds (1577), eclipsing even the Moon. And from the depths of the uninvited heavenly guest, huge tails burst out... Aristotle in the 4th century BC. explained the phenomenon of a comet as follows: light, warm, “dry pneuma” (gases of the Earth) rises to the boundaries of the atmosphere, falls into the sphere of heavenly fire and ignites - this is how “tailed stars” are formed. Aristotle argued that comets cause severe storms and drought. His ideas have been generally accepted for two thousand years. In the Middle Ages, comets were considered harbingers of wars and epidemics. Thus, 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. While studying the appearance of a comet in 1577, Tycho Brahe determined that it was moving far beyond the orbit of the Moon. The time for studying the orbits of comets had begun... The first fanatic eager to discover comets was an employee of the Paris Observatory, Charles Messier. He entered the history of astronomy as the 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. The catalog includes open and globular clusters and galaxies. The Andromeda nebula is named M31 in the Messier catalogue. Over 39 years of observations, Messier discovered 14 new comets! In the first half XIX century Among the “catchers” of comets, Jean Pons especially distinguished himself. A watchman at the Marseilles Observatory, and later its director, he decided to join in the observations of tailed “stars”. Pons built a small amateur telescope and, following the example of his compatriot Messier, began searching for comets. The matter turned out to be so fascinating that in 26 years he discovered 33 new comets! It is no coincidence that astronomers nicknamed it the “Comet Magnet.” The record set by Pons remains unsurpassed to this day. Comets are discovered every year. On average, about 20 of them open per year. About 50 comets are available for observation, and over the entire history of mankind, about two thousand appearances of comets have been observed.
Halley's Comet moves in an elliptical orbit in the direction opposite to the direction of rotation of the planets.
Halley's Comet in the sky over Georgia, USA. The photo was taken in March 1986. The orbits of most comets are highly elongated ellipses. In 1702, Edmund Halley proved that the comets of 1531, 1607 and 1682 had the same orbit. It turns out that comets are coming back! The period of revolution around the Sun of Comet Halley is 76 years, the semimajor axis of the orbit is 17.8 AU, the eccentricity is 0.97, the inclination of the orbit to the ecliptic plane is 162.2°, the distance at perihelion is 0.59 AU. The last date of perihelion passage is 1986. In 2000, Comet Halley is located between the orbits of Uranus and Neptune. The aphelion of the orbit of Comet Halley is far beyond the orbit of Neptune.
Comet Hale-Bopp, 1997. Comet Hale–Bopp was discovered simultaneously by two amateur astronomers in 1995 as a 10th magnitude object. Using the telescope. Hubble discovered hydroxyl OH in the comet's atmosphere, which is formed as a result of the breakdown of water molecules under the influence of ultraviolet radiation from the Sun. 15-meter radio telescope at Hawaiian Islands emission of molecules of cyanide acid, the strongest poison, was recorded in the comet! In the gaseous shell of the celestial guest, the glow of many other molecules characteristic of the composition of comets, for example, carbon monoxide, cyanide, and ammonia decomposition products, was noted. According to experts, the diameter of the nucleus of comet Hale-Bopp is at least 50 kilometers. The latter means that it is at least 100 times more massive than the nucleus of Comet Halley. On March 23, 1997, the comet passed at its shortest distance from the Earth - 196 million kilometers, then began to move away from the Sun. The comet's orbital period is 3000 years. Far from the Sun, near aphelion, comets remain for a longer time than near perihelion. The farther a comet is from the Sun, the lower its temperature. In this case, the material of the comet stops evaporating, the tail and coma disappear, the apparent magnitude of the comet increases, and it ceases to be visible. Near perihelion, comets move at high speeds and form a huge tail.
Comets are the most numerous and most amazing celestial bodies in the Solar System. According to scientists, on the far outskirts of the Solar system, in the so-called Oort cloud - a giant spherical accumulation of cometary matter - there are about 1012-1013 comets concentrated, orbiting the Sun at distances from 3000 to 160,000 AU, which is half the distance to the nearest stars Under the influence of disturbances from nearby stars, some comets leave the solar system forever. Others, on the contrary, rush towards the Sun in highly elongated orbits and, thanks to a sharp increase in the flow of solar radiation, become ordinary comets. There, under the influence of the gravity of the giant planets, they can move into elliptical orbits.
Comet Hyakutake, which appeared in 1996.
Comet Shoemaker-Levy 9 came close to Jupiter in 1992 and was torn apart by the force of its gravity, and in July 1994 its fragments collided with Jupiter, causing fantastic effects in the planet's atmosphere.
With each approach to the Sun, the comet loses some of its mass in the form of gas and dust, ejected into the head and tail. At the same time, the heads of comets sometimes reach sizes exceeding the size of the Sun, and the tails sometimes have a length of more than 1 AU. The 1888 comet had a tail whose dimensions exceeded the distance from the Sun to Jupiter! Spectral studies show that the comet contains both gas and dust components; the latter shines only with reflected sunlight. The same can be said for the brightest central part of the comet's head, which observers usually call the nucleus. In 1986, Halley's comet was explored by the spacecraft Vega-1, Vega-2, and Giotto. The nucleus of Comet Halley is cosmic body measuring 14×7.5×7.5 km and weighing 6,1014 kg. The comet's nucleus rotates slowly with a period of 53 hours. The comet's surface is very dark, with an albedo of 0.04. Surface temperature at a distance of 0.8 AU. was about 360 K. Carbon dioxide and dust were found in the emitted jets. Every second near perihelion, the comet ejects 45 tons of gas and 8 tons of dust. 
Halley's Comet March 13, 1986 near the Milky Way. According to the hypothesis of the famous American researcher Fred Whipple, the cometary nucleus is an ice block consisting of a mixture of frozen water and frozen gases interspersed with refractory rocky and metal particles, meteoric matter. Figuratively speaking, it looks like a “polluted iceberg.” The “ices” of the cometary nucleus consist of simple compounds of hydrogen, oxygen, carbon and nitrogen, and as such an iceberg approaches the Sun, they begin to evaporate intensively. Then all the blocks and stones included in the ice with a diameter from several meters to centimeters and millimeters are exposed and, in turn, release adsorbed gases and supply dust. They can form a swarm of independent boulders and stones. Fountains of gas can even change the comet's orbit. An extensive luminous gas shell - a coma - forms around the core. Together with the nucleus, it makes up the head of the comet. Further approach of the comet to the Sun leads to the fact that its head becomes oval, then lengthens and a tail develops from it. Most often, the tails of comets are directed away from the Sun due to the pressure of sunlight on gas molecules and dust particles released from the cometary nucleus. The comet's nucleus is not a solid single body, even of asteroid size, but a collection of individual bodies. These bodies (blocks, stones, grains of sand, specks of dust) are weakly connected with each other, but still form a single whole for the time being. However, with each approach to the Sun, the periodic comet becomes fainter. Some of them are quite “strong”: for example, Halley’s comet with a longer period, 76 years, has been observed since 466 BC. e. Over the past millennia, it has passed perihelion 32 times. Comet Encke with a period of 3.3 years was discovered in 1786 and during this time experienced more than a dozen of its tails. However, over these two centuries, its absolute magnitude has increased by no less than 2m. And there are those that “cannot withstand” more than two or three approaches to the Sun and, disintegrating, give rise to a meteorite swarm that continues to move along the old orbit. At his meeting with the Earth we observe meteor shower.
There are frequent cases when comets are split into several parts, thereby demonstrating the low coherence of its substance. A classic example is Comet Biela. It was discovered in 1772 and observed in 1815, 1826 and 1832. In 1845, the size of the comet was increased, and in January 1846, observers were surprised to discover two very close comets instead of one. The relative motions of both comets were calculated, and it turned out that Comet Biela split into two about a year ago, but at first the components were projected on top of each other, and the separation was not immediately noticed. Comet Biela was observed one more time, with one component being much fainter than the other. Couldn't find her again. But a meteor shower was repeatedly observed, the orbit of which coincided with the orbit of Comet Biela.
Halley's Comet March 12, 1986. White dust and blue plasma tails are clearly visible. Two "scratching" comets were first observed by the SOLWIND satellite in close proximity from the Sun in the shadow of an artificial disk. It was moved many meters ahead of the device and created an imitation solar eclipse in the absence of atmospheric interference. In January and July 1981, comets were observed at distances from the Sun slightly greater than its radius, and even in the solar corona did not cease to exist. It is safe to say that the entire dust component of these comets evaporated in the solar corona, but the larger bodies that entered the comet’s nucleus (rocky blocks) “survived” the extremely high temperature during several hours of being in the corona and escaped along the original orbit, moving away from the Sun as a cluster of small solid bodies and already invisible. Since then, comets flying near the Sun have been regularly discovered.
Source of information: "Open Astronomy 2.5", LLC "PHYSICON"
Comets- (from Greek kometes - “star with a tail”, “comet”, “shaggy”; literally - "long-haired"), small bodies of the Solar System, revolving around the Sun in elongated orbits and having the appearance of nebulous objects, usually with a light clump - a core in the center and a tail. As it approaches the Sun, the comet's tail, formed by gases evaporating under the sun's heat, enlarges.
Comet Hale-Bopp 1996
Presumably, long-period comets come to us from the “Oort Cloud,” located on the outer boundaries of the Solar System, in which millions of cometary nuclei circulate.
Comets are shapeless blocks only a few kilometers in size, consisting of ice mixed with dust particles. Comets move in very elongated orbits, spending most of the time far from the Sun, where they remain invisible, and when they approach the Sun, ice begins to melt under the influence of solar heat, evaporating and escaping into interplanetary space along with other gases. As a result, many comets, passing near the Sun, take on a very unusual appearance.
Most comets that periodically appear in the vicinity of the Sun are rather faint objects. The exception is Halley's Comet, which appears before us as a very bright and impressive object on almost every return to the Sun.
In fact, the brightest and most spectacular comets appear unexpectedly in the sky, many of them perhaps approaching the Sun for the first time. Those few weeks during which a bright comet quickly circles the Sun, then disappearing forever or perhaps for many millennia in space, are the hottest time for cometary astronomers. In rare cases, especially if a comet comes too close to the Sun, it can break into pieces that are later observed as separate bodies (comet nuclear decay).
Orbit of a periodic comet and tail formation
What are they made of?
Comets look different. Everyone has a foggy gas envelope - coma, which together with the nucleus forms the head of the comet. Even if the comet is in close proximity to the Sun, its head appears to be nothing more than a hazy speck. The most remarkable feature of most comets is tail. It is brightest when the comet is near the perihelion of its orbit. Here, the heat flow from the Sun is especially significant, under the influence of which gases and dust evaporate from the comet into outer space. Some comets have two tails: one is curved, consisting of dust particles; the other is straight, gaseous, elongated in the direction exactly opposite to the direction of the Sun. A number of comets have been observed to have multiple (dust) tails.
Length comet tails can reach tens and hundreds of millions of kilometers; comets were observed whose tails stretched almost half the sky. It is assumed that the dust lost by comets, entering interplanetary space, gives rise to meteoroid bodies, which later, colliding at high speed with the earth's atmosphere, are discovered in the form of meteors. Dust grains from comet tails also replenish interplanetary dust clouds, which, scattering the sun's rays, give rise to a phenomenon called zodiacal light.
Core comets are sometimes visible inside the coma as a bright star-shaped object in which no details can be discerned even with the largest telescopes. Sometimes the nucleus can be confused with various structural formations in a coma - such as a shell or ejections of matter from the comet's nucleus. Comet nuclei were studied in detail by spacecraft that approached comets.
In 2005, NASA's Deep Impact spacecraft rammed Comet Tempel 1 and transmitted images of its surface.
The nucleus of Comet Tempel 1 (photo by the Deep Impact apparatus)
Comet observations
Any instrument can be used to observe comets. Experience shows that giant comet tails can be detected with the naked eye, binoculars and telescopes with a wide field of view. But to see the complex structure of a comet near its nucleus, telescopes with large apertures and high magnification are needed.
Sketches of comets can be made during observations using any instruments; the technique is the same as for sketching planets.
Photographing comets
Photographs help not only determine the exact position of the comet's head, but also provide an image of its tail, as well as see fine details that, due to their low brightness, cannot be seen in other ways.
With an instrument equipped with a clock mechanism, you can try to take a photograph of the comet. With a long-focus refractor, sometimes a shutter speed of 5-10 minutes is enough to get a clear image of the comet's nucleus.
To track a comet, taking into account its own movement among the stars, the telescope (or camera) must be equipped with a guidance system. In this case, the images of stars in the photographs will appear in the form of dashes. When using short-focus lenses, guiding can be done directly by the stars.
For photographing a comet's tail, a short-focus fast camera is preferable. A large aperture makes it possible, with a not very long shutter speed, to get the tail of a comet far from the head in the photograph. Such a photograph can give an idea of the structure of the comet.
Comet designations
Until 1995, the order in which comets were designated was as follows. At the beginning, the comet was designated by the year of discovery and a small letter of the Latin alphabet (in order of discovery). The final designation of the comet consisted of the year, the number (Roman numeral) in the order of the moments of perihelion passage, and the surname of the discoverer (or two or three surnames of the persons who independently discovered the comet). For example, comet 1957f=1957 IX was called comet Latyshev-Wild-Burnham.
Since January 1995, a new rule for naming comets has been in effect, and it extends back to all comets of the past with well-known orbits. Now after the year number they put a Latin letter (from A to Y), indicating in which half of which month the discovery took place: A - from January 1 to 15, B - from January 16 to 31, C - from February 1 to 15, etc. .d. The letter I is not used so as not to confuse it with the number 1 and the letter J. After the letter they put a number - the serial number of the opening in this half of the month.
Before the opening date, one letter indicates the “status” of the object:
P (periodic) - a comet with an orbital period of less than 200 years;
C (comet) - long period comet, with a period of more than 200 years;
D (disappear) - disappeared comet;
X is a comet for which it was not possible to calculate the orbit accurately enough.
For periodic comets, instead of the discovery date, there is a serial number in front of the calculation of the exact orbit (this is reminiscent of the designation system for asteroids), for example, Halley's comet now has a permanent designation: IP/Halley, and comet Encke - 2P/Enske.
Now the names of astronomers need not be written, although traditionally they still do this and sometimes even put them in front, for example, Tempel-Tuttle (55Р). The old designation for Comet Shoemaker-Levy 9 (which fell on Jupiter) was 1993e, and the new one is D/1993 F2.
Finally
The masses of comets are very small - about a billion times less than the mass of our Earth, and the density of matter in their tails is practically zero. Therefore, “heavenly guests” do not in any way affect the planets of the solar system, much less the lives of people. In May 1910, for example, the Earth passed through the tail of Comet Halley, but no changes in the movement of our planet occurred and no clearly related phenomena were noticed on Earth. However, history preserves the fear and fear of our ancestors before these heavenly wanderers. And very often one can find in ancient chronicles and chronicles references to the appearance bright comets in the sky and the connection of these phenomena with earthly incidents - fires, wars and even the deaths of individual people.
Vintage image of a comet
On the other hand, the collision of a large comet with a planet can cause large-scale effects in the atmosphere and magnetosphere of the planet. A good and fairly well-studied example of such a collision was the collision of debris from comet Shoemaker-Levy 9 with Jupiter in July 1994.
Let us hope that the growing scientific and technical potential of our civilization will help in the future to protect Earthlings from death in the event of a dangerous collision with the Earth of a large nucleus of a comet.
Materials used:
Kulikovsky P. G. Handbook for an Astronomy Amateur / Ed. V. G. Surdina. Ed. 5th, revised and full updated - M.: Editorial URSS, 2002. - 688 p.
- Dunlop S. ABC of the starry sky: Trans. from English/Ed. and with a preface. A. V. Kozenko. M.: Mir, 1990. - 238 pp., ill.
- Website astropage.ru
- Wikipedia website
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Comets. Properties of comets
A special place among the small bodies of the Solar System is occupied by comets - celestial bodies moving around the Sun in very elongated orbits. As the ice approaches the Sun, it melts and comets form a huge tail of gas. The tail occurs due to the fact that the comet's nucleus begins to boil and evaporate under the influence of sunlight, since it consists of water ice mixed with dust. The boiling-off material is blown away from the nucleus by the solar wind, so the tail is directed away from the Sun, and not along the trajectory of the comet, so that sometimes the tail even moves in front of the comet! Usually, after flying around the sun, comets return to the boundaries of the solar system. Periodic comets approach the Sun again after a certain period of time, their appearance can be predicted - for example, famous comet Halley (named after its discoverer, the English astronomer E. Halley), which was observed before our era, appears once every 76 years. Halley's Comet was the first of a class of periodic comets.
Periodic comets move in less elongated elliptical orbits and have completely different characteristics. Of the 40 comets observed more than once, 35 have orbits inclined less than 45º to the ecliptic plane. Only Halley's comet has an orbit with an inclination greater than 90º and, therefore, moves in reverse direction. Among short-period (i.e., having periods of 3-10 years) comets, the “Jupiter family” stands out large group comets whose aphelion is removed from the Sun at the same distance as that of Jupiter. It is assumed that the “Jupiter family” was formed as a result of the planet’s capture of comets that had previously moved in more elongated orbits. Depending on the relative position of Jupiter and the comet, the eccentricity of the comet's orbit can either increase or 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 because it passed near Jupiter or Saturn and abruptly changed its orbit. 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 disappearance of comets. It has been reliably established that comets are quickly destroyed. The brightness of short-period comets fades over time, and in some cases the destruction process has been observed almost directly. A classic example is Comet Biely. It was discovered in 1772 and observed in 1813, 1826, 1832. In 1845, the size of the comet was increased, and in January 1846, observers were surprised to discover two very close comets instead of one. Biely calculated the relative movements of both comets, and it turned out that Biely's comet 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 Biely was observed one more time, with one component much fainter than the other, and it could not be found again. But a meteor shower was repeatedly observed, the orbit of which coincided with the orbit of Comet Biely.
When deciding the question of the origin of comets, one cannot do without knowledge of the chemical composition of the substance from which the cometary nucleus is composed. It would seem, what could be simpler? 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 core can be simply the reflected solar spectrum or the emission molecular spectrum. The reflected solar spectrum is continuous and does not reveal anything about chemical composition the area from which it was reflected - the core or the dust atmosphere surrounding the core. The emission gas spectrum carries information about the chemical composition of the gas atmosphere surrounding the core, and also does not tell us anything about the chemical composition of the surface layer of the core, 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 perinuclear space, are quickly exposed to the destructive action of the solar wind and photons, or disintegrate, or dissociate into simpler molecules, the emission spectra of which can be observed from comets. The parent molecules themselves produce a continuous spectrum.
But there are also non-periodic comets - they fly away and do not return, and some fall into the Sun and burn up. The comet's tail can only be observed on a dark night. The core appears as a more or less bright star that crosses the sky over the course of a few days.
There are apparently hundreds of billions of comets in the solar system, but only a few are observable from Earth. A rare and unusual sight, comets have long attracted people's attention. In ancient times, their appearance was considered a bad omen. Comet detection is popular among amateur astronomers these days; The comet is named after its discoverers.
Comet research
Project Vega was one of the most complex spacecraft explorations of the Solar System in history. It consisted of three parts: studying the atmosphere and surface of Venus using landing vehicles, studying the dynamics of the atmosphere of Venus using balloon probes (balloons were the first in the world to be launched into the atmosphere from another planet), a flight through the gas and dust atmosphere (coma) and the plasma shell of Halley's comet.
The automatic interplanetary station "Vega-1" launched from the Baikonur Cosmodrome on December 15, 1984. It was followed 6 days later by Vega-2. The course was set for the planet Venus. In June 1985 They passed one after another near Venus. Before the flyby of the planet, the descent vehicles separated from them, entering at the second cosmic speed, and the atmosphere of Venus, and each of them was divided into two parts - the landing vehicle and the balloon probe. Using the lander, a series of experiments was carried out to study the atmosphere and surface of the planet. The balloon probes drifted at an altitude of about 54 kilometers, and for two days their movement was recorded by a network of ground-based radio telescopes. The first two parts of the program, dedicated to the study of Venus, were successfully completed.
But the most interesting was the third part of the research project on Halley’s comet. This heavenly body left a deep imprint in the memory of mankind, approaching the Sun about thirty times over the course of 2 millennia. And, starting with the bold hypothesis put forward by E. Halley, it was the object of systematic research in astronomy. By the inexorable logic of the space age, comets should have become objects of direct research. For the first time, the spacecraft had to “see” the comet’s nucleus, which was elusive to ground-based telescopes. The meeting of Vega 1 with the comet occurred on March 6, and Vega 2 on March 9, 1986. They passed at a distance of 8900-8000 kilometers from its core.
The project was implemented with broad international cooperation and with the participation of scientific organizations from many countries.
In addition to Vega-1 and Vega-2, others also headed towards Halley’s comet spacecraft- "Giotto", equipped by the European Space Agency, and two small Japanese devices "Suisei" ("Comet") and "Sakigake" ("Pioneer").
Interest in comet research has increased. Over the past 20 years, the USSR and the USA have sent more than 30 interplanetary automatic stations to the planets. Their flights expanded our understanding of the planets and their satellites. But the time has come to remember about other family members, in particular about comets.
Comets are guests who arrived from the very distant outskirts of the solar system. It is assumed that about 100 billion comets are constantly located in the cometary cloud surrounding the Sun at a distance 10 thousand times greater than from the Sun to the Earth. Their fate is different. Most of them remain for billions of years, some leave the Solar System, and some move across its interior and even fall into orbits with a relatively short period, like Halley's comet.