Some of the famous comets. Information about comets. Movement of comets. Names of comets What types of comets are there?
COMET
a small celestial body moving in interplanetary space and abundantly releasing gas when approaching the Sun. A variety of physical processes are associated with comets, from sublimation (dry evaporation) of ice to plasma phenomena. Comets are the remnants of the formation of the Solar System, a transitional stage to interstellar matter. The observation of comets and even their discovery are often carried out by amateur astronomers. Sometimes comets are so bright that they attract everyone's attention. In the past, the appearance of bright comets caused fear among people and served as a source of inspiration for artists and cartoonists.
Movement and spatial distribution. All or almost all comets are components of the Solar System. They, like the planets, obey the laws of gravity, but they move in a very unique way. All planets revolve around the Sun in the same direction (which is called “forward” as opposed to “reverse”) in almost circular orbits lying approximately in the same plane (the ecliptic), and comets move in both forward and backward directions along highly elongated ( eccentric) orbits inclined at different angles to the ecliptic. It is the nature of the movement that immediately gives away the comet. Long-period comets (with orbital periods of more than 200 years) come from regions thousands of times farther than the most distant planets, and their orbits are tilted at all sorts of angles. Short-period comets (periods of less than 200 years) come from the region of the outer planets, moving in a forward direction in orbits lying close to the ecliptic. Far from the Sun, comets usually do not have "tails" but sometimes have a barely visible "coma" surrounding the "nucleus"; together they are called the "head" of the comet. As it approaches the Sun, the head enlarges and a tail appears.
Structure. In the center of the coma there is a core - a solid body or a conglomerate of bodies with a diameter of several kilometers. Almost all of the comet's mass is concentrated in its nucleus; this mass is billions of times less than the earth's. According to F. Whipple's model, the comet's nucleus consists of a mixture of various ices, mainly water ice with an admixture of frozen carbon dioxide, ammonia and dust. This model is confirmed by both astronomical observations and direct measurements from spacecraft near the nuclei of comets Halley and Giacobini-Zinner in 1985-1986. When a comet approaches the Sun, its core heats up and the ice sublimates, i.e. evaporate without melting. The resulting gas scatters in all directions from the nucleus, taking with it dust particles and creating a coma. Water molecules destroyed by sunlight form a huge hydrogen corona around the comet's nucleus. In addition to solar attraction, repulsive forces also act on the rarefied matter of a comet, due to which a tail is formed. Neutral molecules, atoms and dust particles are affected by the pressure of sunlight, while ionized molecules and atoms are more strongly affected by the pressure of the solar wind. The behavior of the particles that form the tail became much clearer after direct study of comets in 1985-1986. The plasma tail, consisting of charged particles, has a complex magnetic structure with two regions of different polarity. On the side of the coma facing the Sun, a frontal shock wave is formed, exhibiting high plasma activity.
Although the tail and coma contain less than one millionth of the comet's mass, 99.9% of the light comes from these gas formations, and only 0.1% from the nucleus. The fact is that the core is very compact and also has a low reflection coefficient (albedo). The particles lost by the comet move in their orbits and, entering the atmospheres of the planets, cause the formation of meteors ("shooting stars"). Most of the meteors we observe are associated with cometary particles. Sometimes the destruction of comets is more catastrophic. Comet Bijela, discovered in 1826, split into two parts in front of observers in 1845. When this comet was last seen in 1852, the pieces of its nucleus were millions of kilometers away from each other. Nuclear fission usually heralds the complete disintegration of a comet. In 1872 and 1885, when Bijela's comet, if nothing had happened to it, would have crossed the Earth's orbit, unusually heavy meteor showers were observed.
see also
METEOR ;
METEORITE. Sometimes comets are destroyed when approaching planets. On March 24, 1993, at the Mount Palomar Observatory in California, astronomers K. and Y. Shoemaker, together with D. Levy, discovered a comet with an already destroyed nucleus near Jupiter. Calculations showed that on July 9, 1992, the Shoemaker-Levy-9 comet (this is the ninth comet they discovered) passed near Jupiter at a distance of half the radius of the planet from its surface and was torn apart by its gravity into more than 20 parts. Before destruction, the radius of its core was approx. 20 km.
Table 1.
MAIN GAS COMPONENTS OF COMETS
Stretching out in a chain, the fragments of the comet moved away from Jupiter in an elongated orbit, and then in July 1994 approached it again and collided with the cloudy surface of Jupiter.
Origin. Comet nuclei are the remnants of the primary matter of the Solar System, which made up the protoplanetary disk. Therefore, their study helps to restore the picture of the formation of planets, including the Earth. In principle, some comets could come to us from interstellar space, but so far not a single such comet has been reliably identified.
Gas composition. In table Table 1 lists the main gas components of comets in descending order of their content. The movement of gas in the tails of comets shows that it is strongly influenced by non-gravitational forces. The glow of the gas is excited by solar radiation.
ORBITS AND CLASSIFICATION
To better understand this section, we recommend that you read the following articles:
CELESTIAL MECHANICS;
CONIC SECTIONS;
ORBIT;
SOLAR SYSTEM .
Orbit and speed. The movement of the comet's nucleus is completely determined by the attraction of the Sun. The shape of a comet's orbit, like any other body in the Solar System, depends on its speed and distance from the Sun. The average speed of a body is inversely proportional to the square root of its average distance to the Sun (a). If the speed is always perpendicular to the radius vector directed from the Sun to the body, then the orbit is circular, and the speed is called circular speed (vc) at a distance a. The speed of escape from the gravitational field of the Sun along a parabolic orbit (vp) is times greater than the circular speed at this distance. If the comet's speed is less than vp, then it moves around the Sun in an elliptical orbit and never leaves the Solar System. But if the speed exceeds vp, then it moves around the Sun in an elliptical orbit and never leaves the Solar System. But if the speed exceeds vp, then the comet passes by the Sun once and leaves it forever, moving along a hyperbolic orbit. The figure shows the elliptical orbits of the two comets, as well as the nearly circular orbits of the planets and a parabolic orbit. At the distance that separates the Earth from the Sun, the circular speed is 29.8 km/s, and the parabolic speed is 42.2 km/s. Near Earth, the speed of Comet Encke is 37.1 km/s, and the speed of Comet Halley is 41.6 km/s; This is why Comet Halley goes much further from the Sun than Comet Encke.
Classification of cometary orbits. Most comets have elliptical orbits, so they belong to the Solar System. True, for many comets these are very elongated ellipses, close to a parabola; along them, comets move away from the Sun very far and for a long time. It is customary to divide the elliptical orbits of comets into two main types: short-period and long-period (almost parabolic). The orbital period is considered to be 200 years.
SPATIAL DISTRIBUTION AND ORIGIN
Almost parabolic comets. Many comets belong to this class. Since their orbital periods are millions of years, only one ten-thousandth of them appears in the vicinity of the Sun over the course of a century. In the 20th century observed approx. 250 such comets; therefore, there are millions of them in total. In addition, not all comets come close enough to the Sun to become visible: if the perihelion (the point closest to the Sun) of the comet’s orbit lies beyond the orbit of Jupiter, then it is almost impossible to notice it. Taking this into account, in 1950 Jan Oort suggested that the space around the Sun at a distance of 20-100 thousand AU. (astronomical units: 1 AU = 150 million km, distance from the Earth to the Sun) is filled with comet nuclei, the number of which is estimated at 1012, and the total mass is 1-100 Earth masses. The outer boundary of the Oort “comet cloud” is determined by the fact that at this distance from the Sun the movement of comets is significantly influenced by the attraction of neighboring stars and other massive objects (see below). Stars move relative to the Sun, their disturbing influence on comets changes, and this leads to the evolution of cometary orbits. So, by chance, a comet may end up in an orbit passing close to the Sun, but on the next revolution its orbit will change slightly, and the comet will pass away from the Sun. However, instead of it, “new” comets will constantly fall from the Oort cloud into the vicinity of the Sun.
Short-period comets. When a comet passes near the Sun, its core heats up and the ice evaporates, forming a gas coma and tail. After several hundreds or thousands of such flights, there are no fusible substances left in the core, and it ceases to be visible. For short-period comets that regularly approach the Sun, this means that their populations should become invisible in less than a million years. But we observe them, therefore, replenishment from “fresh” comets is constantly arriving. Replenishment of short-period comets occurs as a result of their “capture” by planets, mainly Jupiter. It was previously thought that long-period comets coming from the Oort cloud were captured, but it is now believed that their source is a cometary disk called the “inner Oort cloud.” In principle, the idea of the Oort cloud has not changed, but calculations have shown that the tidal influence of the Galaxy and the influence of massive clouds of interstellar gas should destroy it quite quickly. A source of replenishment is needed. Such a source is now considered to be the inner Oort cloud, which is much more resistant to tidal influences and contains an order of magnitude more comets than the outer cloud predicted by Oort. After each approach of the Solar System to a massive interstellar cloud, comets from the outer Oort cloud scatter into interstellar space, and they are replaced by comets from the inner cloud. The transition of a comet from an almost parabolic orbit to a short-period orbit occurs when it catches up with the planet from behind. Typically, capturing a comet into a new orbit requires several passes through the planetary system. The resulting orbit of a comet typically has low inclination and high eccentricity. The comet moves along it in a forward direction, and the aphelion of its orbit (the point farthest from the Sun) lies close to the orbit of the planet that captured it. These theoretical considerations are fully confirmed by the statistics of cometary orbits.
Non-gravitational forces. Gaseous sublimation products exert reactive pressure on the comet's nucleus (similar to the recoil of a gun when fired), which leads to the evolution of the orbit. The most active outflow of gas occurs from the heated “afternoon” side of the core. Therefore, the direction of the pressure force on the core does not coincide with the direction of solar rays and solar gravity. If the axial rotation of the nucleus and its orbital revolution occur in the same direction, then the pressure of the gas as a whole accelerates the movement of the nucleus, leading to an increase in the orbit. If rotation and circulation occur in opposite directions, then the comet’s movement is slowed down and the orbit is shortened. If such a comet was initially captured by Jupiter, then after some time its orbit is entirely in the region of the inner planets. This is probably what happened to Comet Encke.
Comets touching the Sun. A special group of short-period comets consists of comets that “graze” the Sun. They were probably formed thousands of years ago as a result of the tidal destruction of a large core, at least 100 km in diameter. After the first catastrophic approach to the Sun, fragments of the nucleus made approx. 150 revolutions, continuing to fall apart. Twelve members of this family of Kreutz comets were observed between 1843 and 1984. Their origins may be related to a large comet seen by Aristotle in 371 BC.
Halley's Comet. This is the most famous of all comets. It has been observed 30 times since 239 BC. Named in honor of E. Halley, who, after the appearance of the comet in 1682, calculated its orbit and predicted its return in 1758. The orbital period of Halley's comet is 76 years; it last appeared in 1986 and will next be observed in 2061. In 1986, it was studied at close range by 5 interplanetary probes - two Japanese (Sakigake and Suisei), two Soviet (Vega-1 and Vega-1). 2") and one European ("Giotto"). It turned out that the comet's nucleus is potato-shaped, approx. 15 km and width approx. 8 km, and its surface is “blacker than coal.” It may be covered with a layer of organic compounds, such as polymerized formaldehyde. The amount of dust near the core turned out to be much higher than expected. See also HALLEY, EDMUND.
Comet Encke. This faint comet was the first to be included in the Jupiter family of comets. Its period of 3.29 years is the shortest among comets. The orbit was first calculated in 1819 by the German astronomer J. Encke (1791-1865), who identified it with the comets observed in 1786, 1795 and 1805. Comet Encke is responsible for the Taurid meteor shower, observed annually in October and November.
Comet Giacobini-Zinner. This comet was discovered by M. Giacobini in 1900 and rediscovered by E. Zinner in 1913. Its period is 6.59 years. It was with it that on September 11, 1985, the space probe "International Cometary Explorer" first approached, which passed through the tail of the comet at a distance of 7800 km from the nucleus, thanks to which data was obtained on the plasma component of the tail. This comet is associated with the Jacobinids (Draconids) meteor shower.
PHYSICS OF COMETS
Core. All manifestations of a comet are somehow connected with the nucleus. Whipple suggested that the comet's nucleus was a solid body consisting mainly of water ice with dust particles. This “dirty snowball” model easily explains the multiple passages of comets near the Sun: with each passage, a thin surface layer (0.1-1% of the total mass) evaporates and the inner part of the nucleus is preserved. Perhaps the core is a conglomerate of several “cometesimals,” each no more than a kilometer in diameter. Such a structure could explain the disintegration of nuclei, as observed with Comet Biela in 1845 or Comet West in 1976.
Shine. The observed brightness of a celestial body illuminated by the Sun with a constant surface changes in inverse proportion to the squares of its distances from the observer and from the Sun. However, sunlight is scattered mainly by the comet's gas and dust shell, the effective area of which depends on the rate of ice sublimation, and that, in turn, on the heat flux incident on the nucleus, which itself varies inversely with the square of the distance to the Sun. Therefore, the brightness of the comet should vary in inverse proportion to the fourth power of the distance to the Sun, which is confirmed by observations.
Kernel size. The size of the comet's nucleus can be estimated from observations at a time when it is far from the Sun and not shrouded in a gas and dust envelope. In this case, light is reflected only by the solid surface of the core, and its apparent brightness depends on the cross-sectional area and reflectance (albedo). The albedo of the nucleus of Comet Halley turned out to be very low - approx. 3%. If this is also typical for other nuclei, then the diameters of most of them lie in the range from 0.5 to 25 km.
Sublimation. The transition of matter from a solid to a gaseous state is important for the physics of comets. Measurements of the brightness and emission spectra of comets have shown that the melting of the main ices begins at a distance of 2.5-3.0 AU, as it should be if the ice is mainly water. This was confirmed by studying the comets Halley and Giacobini-Zinner. The gases observed first as the comet approaches the Sun (CN, C2) are probably dissolved in water ice and form gas hydrates (clathrates). How this "composite" ice will sublimate depends largely on the thermodynamic properties of the water ice. Sublimation of the dust-ice mixture occurs in several stages. Streams of gas and small and fluffy dust particles picked up by them leave the core, since the attraction at its surface is extremely weak. But the gas flow does not carry away dense or interconnected heavy dust particles, and a dust crust is formed. Then the sun's rays heat the dust layer, the heat passes in, the ice sublimates, and gas flows break through, breaking the dust crust. These effects became apparent during the observation of Halley's comet in 1986: sublimation and outflow of gas occurred only in a few regions of the comet's nucleus illuminated by the Sun. It is likely that ice was exposed in these areas, while the rest of the surface was covered with crust. The released gas and dust form the observable structures around the comet's nucleus.
Coma. Dust grains and gas of neutral molecules (Table 1) form an almost spherical coma of the comet. Usually the coma stretches from 100 thousand to 1 million km from the nucleus. Light pressure can deform the coma, stretching it in an anti-solar direction.
Hydrogen corona. Since the core ices are mainly water, the coma mainly contains H2O molecules. Photodissociation breaks down H2O into H and OH, and then OH into O and H. The fast-moving hydrogen atoms fly far from the nucleus before they become ionized, and form a corona, the apparent size of which often exceeds the solar disk.
Tail and related phenomena. The tail of a comet may consist of molecular plasma or dust. Some comets have both types of tails. The dust tail is usually uniform and stretches for millions and tens of millions of kilometers. It is formed by dust grains thrown away from the core in the antisolar direction by the pressure of sunlight, and has a yellowish color because the dust grains simply scatter sunlight. The structures of the dust tail can be explained by the uneven eruption of dust from the core or the destruction of dust grains. The plasma tail, tens or even hundreds of millions of kilometers long, is a visible manifestation of the complex interaction between the comet and the solar wind. Some molecules that leave the nucleus are ionized by solar radiation, forming molecular ions (H2O+, OH+, CO+, CO2+) and electrons. This plasma impedes the movement of the solar wind, which is permeated by a magnetic field. When the comet hits the comet, the field lines wrap around it, taking the shape of a hairpin and creating two areas of opposite polarity. Molecular ions are captured in this magnetic structure and form a visible plasma tail in its central, densest part, which has a blue color due to the spectral bands of CO+. The role of the solar wind in the formation of plasma tails was established by L. Bierman and H. Alfven in the 1950s. Their calculations confirmed measurements from spacecraft that flew through the tails of comets Giacobini-Zinner and Halley in 1985 and 1986. Other phenomena of interaction with the solar wind, which hits the comet at a speed of approx. 400 km/s and forming a shock wave in front of it, in which the matter of the wind and the head of the comet is compacted. The process of “capture” plays an essential role; its essence is that the neutral molecules of the comet freely penetrate the solar wind flow, but immediately after ionization they begin to actively interact with the magnetic field and are accelerated to significant energies. True, sometimes very energetic molecular ions are observed that are inexplicable from the point of view of the indicated mechanism. The capture process also excites plasma waves in the gigantic volume of space around the nucleus. The observation of these phenomena is of fundamental interest for plasma physics. The “tail break” is a wonderful sight. As is known, in the normal state the plasma tail is connected to the comet's head by a magnetic field. However, often the tail breaks away from the head and lags behind, and a new one is formed in its place. This happens when a comet passes through the boundary of regions of solar wind with an opposing magnetic field. At this moment, the magnetic structure of the tail is rearranged, which looks like a break and the formation of a new tail. The complex topology of the magnetic field leads to the acceleration of charged particles; This may explain the appearance of the fast ions mentioned above.
Collisions in the Solar System. From the observed number and orbital parameters of comets, E. Epic calculated the probability of collisions with the nuclei of comets of various sizes (Table 2). On average, once every 1.5 billion years, the Earth has a chance to collide with a core with a diameter of 17 km, and this can completely destroy life in an area equal to the area of North America. Over the 4.5 billion years of Earth's history, this could have happened more than once. Smaller disasters are much more common: in 1908, the nucleus of a small comet probably entered the atmosphere and exploded over Siberia, causing the lodging of forests over a large area.
Comet Lovejoy. In November 2011, Australian astronomer Terry Lovejoy discovered one of the largest comets of the circumsolar Kreutz group, with a diameter of about 500 meters. It flew through the solar corona and did not burn up, was clearly visible from Earth and was even photographed from the ISS.
Comet McNaught. The first brightest comet of the 21st century, also called the "Great Comet of 2007". Discovered by astronomer Robert McNaught in 2006. In January and February 2007, it was clearly visible to the naked eye for residents of the planet's southern hemisphere. The comet's next return is not coming soon - in 92,600 years.
Comets Hyakutake and Hale-Bopp appeared one after another in 1996 and 1997, competing in brightness. If comet Hale-Bopp was discovered back in 1995 and flew strictly “on schedule,” Hyakutake was discovered only a couple of months before its approach to the Earth.
Comet Lexel. In 1770, comet D/1770 L1, discovered by Russian astronomer Andrei Ivanovich Leksel, passed at a record close distance from Earth - only 1.4 million kilometers. This is about four times farther than the Moon is from us. The comet was visible to the naked eye.
1948 Eclipse Comet. On November 1, 1948, during a total solar eclipse, astronomers unexpectedly discovered a bright comet not far from the Sun. Officially named C/1948 V1, it was the last “sudden” comet of our time. It could be seen with the naked eye until the end of the year.
The big January 1910 comet appeared in the sky a couple of months before Halley's Comet, which everyone was waiting for. The new comet was first noticed by miners from diamond mines in Africa on January 12, 1910. Like many super-bright comets, it was visible even during the day.
The Great March Comet of 1843 is also a member of the Kreutz family of circumsolar comets. It flew only 830 thousand km. from the center of the Sun and was clearly visible from Earth. Its tail is one of the longest among all known comets, two astronomical units (1 AU is equal to the distance between the Earth and the Sun).
The Great September Comet of 1882 is the brightest comet of the 19th century and is also a member of the Kreutz family. It is notable for its long “anti-tail” directed towards the Sun.
The Great Comet of 1680, also known as Kirch's Comet, or Newton's Comet. The first comet discovered using a telescope, one of the brightest comets of the 17th century. Isaac Newton studied the orbit of this comet to confirm Kepler's laws.
Halley's Comet is by far the most famous of all periodic comets. It visits the Solar System every 75-76 years and is clearly visible to the naked eye each time. Its orbit was calculated by the English astronomer Edmund Halley, who also predicted its return in 1759. In 1986, spacecraft explored it, collecting a lot of data on the structure of comets. The next appearance of Halley's Comet will be in 2061.
Of course, there always remains the risk of some stray comet colliding with the Earth, which would entail incredible destruction and the probable death of civilization, but so far this is just a frightening theory. The brightest comets can be visible even during the day, presenting a stunning spectacle. Here are ten of the most famous comets in human history.
Comets of the Solar System have always been of interest to space researchers. The question of what these phenomena are also worries people who are far from studying comets. Let's try to figure out what this celestial body looks like and whether it can influence the life of our planet.
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 comet's tail leaves a trail that is millions of kilometers long. 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, we should start from the orbits of comets. Quite a few of these cosmic bodies pass through the Solar System.
Let's take a closer look at the features of comets:
- Comets are so-called snowballs that pass through their orbit and contain dusty, rocky and gaseous accumulations.
- The celestial body warms up during the period of approach to the main star of the solar system.
- Comets do not have satellites that are characteristic of planets.
- Formation systems in the form of rings are also not typical for comets.
- It is difficult and sometimes unrealistic to determine the size of these celestial bodies.
- Comets do not support life. However, their composition can serve as a certain building material.
Features of the structure of comets
The description of a comet can be divided into characteristics of the nucleus, coma and tail of the object. This suggests that the celestial body under study cannot be called a simple structure.
Comet nucleus
Almost the entire mass of the comet is contained 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 matter of the luminous plane.
There are 3 theories that consider the structure of comet nuclei differently:
- The "dirty snowball" theory. This assumption is the most common and belongs to the American scientist Fred Lawrence Whipple. According to this theory, the solid part of the comet is nothing more than a combination of ice and fragments of meteorite matter. According to this specialist, a distinction is made between old comets and bodies of a younger formation. Their structure is different due to the fact that more mature celestial bodies repeatedly approached the Sun, which melted their original composition.
- The core is composed of dusty material. The theory was announced at the beginning of the 21st century thanks to the study of the phenomenon by the American space station. Data from this exploration indicate that the core is a dusty material of a very friable nature with pores occupying the majority of its surface.
- The core cannot be a monolithic structure. Further hypotheses diverge: they imply a structure in the form of a snow swarm, blocks of rock-ice accumulation and meteorite accumulation due to the influence of planetary gravity.
Comet coma
Together with the nucleus, the head of the comet is formed by a coma, which is a foggy shell of a light color. The trail of such a component of the comet stretches over a fairly long distance: from one hundred thousand to almost one and a half million kilometers from the base of the object.
Three levels of coma can be defined, which look like this:
- Interior chemical, molecular and photochemical composition. Its structure is determined by the fact that the main changes occurring with the comet are concentrated and most activated in this area. Chemical reactions, decay and ionization of neutrally charged particles - all this characterizes the processes that occur in an internal coma.
- Coma of radicals. It consists of molecules that are active in their chemical nature. In this area there is no increased activity of substances, which is so characteristic of an internal coma. However, here too the process of decay and excitation of the described molecules continues in a calmer and smoother mode.
- Coma of atomic composition. It is also called ultraviolet. This region of the comet's atmosphere is observed in the hydrogen Lyman-alpha line in the distant ultraviolet spectral region.
Comet tail
The tail of a comet is a unique spectacle in its beauty and effectiveness. It is usually directed from the Sun and looks like an elongated gas-dust plume. Such tails do not have clear boundaries, and we can say that their color range is close to complete transparency.
Fedor Bredikhin proposed classifying sparkling plumes into the following subspecies:
- Straight and narrow format tails. These components of the comet are directed from the main star of the solar system.
- Slightly deformed and wide-format tails. These plumes are evading the Sun.
- Short and severely deformed tails. This change is caused by a significant deviation from the main star of our system.
- Dust tail. A distinctive visual feature of this element is that its glow has a characteristic reddish tint. A plume of this format is homogeneous in its structure, stretching for a million, or even tens of millions of kilometers. It was formed due to numerous dust particles that the energy of the Sun threw to a long distance. The yellow tint of the tail is due to the dispersion of dust particles by sunlight.
- Tail of the plasma structure. This plume is much more extensive than the dust trail, because its length is tens and sometimes hundreds of millions of kilometers. The comet interacts with the solar wind, which causes a similar phenomenon. As is known, solar vortex flows are penetrated by a large number of fields of a magnetic nature. They, in turn, collide with the comet's plasma, which leads to the creation of a pair of regions with diametrically different polarities. At times, this tail breaks off spectacularly and a new one is formed, which looks very impressive.
- Anti-Tail. It appears according to a different pattern. The reason is that it is directed towards the sunny side. The influence of the solar wind on such a phenomenon is extremely small, because the plume contains large dust particles. It is possible to observe such an antitail only when the Earth crosses the comet’s orbital plane. The disc-shaped formation surrounds the celestial body on almost all sides.
Main types of comets
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 their maximum distance from the Sun, they have no tails, but only a subtle coma. When periodically approaching the main luminary, a plume appears. More than four hundred such comets have been recorded, among which there are short-period celestial bodies with a revolution around the Sun of 3-10 years.
- Comets with long orbital periods. The Oort cloud, according to scientists, periodically supplies such cosmic guests. The orbital term of these phenomena exceeds the two hundred year mark, which makes the study of such objects more problematic. Two hundred and fifty such aliens give reason to believe that in fact there are millions of them. Not all of them are so close to the main star of the system that it becomes possible to observe their activities.
The most famous comets of the solar system
There are a large number of comets that pass through the solar system. But there are the most famous cosmic bodies that are worth talking about.
Halley's Comet
Halley's Comet became known thanks to observations of it by a famous researcher, after whom it received its name. It can be classified as a short-period body, because its return to the main luminary is calculated over a period of 75 years. It is worth noting the change in this indicator towards parameters that fluctuate between 74-79 years. Its fame lies in the fact that it is the first celestial body of this type whose orbit has been 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 frequency directly depends on the gravitational influence of large planets on the life activity of the described object.
The speed of Halley's comet in relation to our planet is amazing because it exceeds all indicators of the activity of the celestial bodies of the Solar System. The approach of the earth's orbital system to the comet's orbit can be observed at two points. This results in two dusty formations, which in turn form meteorite showers called the Aquarids and Oreanids.
If we consider the structure of such a body, it is not much different from other comets. When approaching the Sun, the formation of a sparkling trail is observed. The comet's nucleus is relatively small, which may indicate a pile of debris as building material for the object's base.
You will be able to enjoy the extraordinary spectacle of the passage of Halley's Comet in the summer of 2061. It promises better visibility of the grandiose phenomenon compared to the more than modest visit in 1986.
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 that it is one of the brightest comets of the last century.
The phenomenality of this discovery lies in the fact that in the late 90s the comet was observed without special equipment for ten months, which in itself cannot but surprise.
The shell of the solid core of a celestial body is quite heterogeneous. Icy areas of unmixed gases are combined with carbon monoxide and other natural elements. The discovery of minerals that are characteristic of the structure of the earth's crust and some meteorite formations once again confirm that Comet Hale-Bop originated within our system.
The influence of comets on the life of planet Earth
There are many hypotheses and assumptions regarding 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 the time. This happened almost immediately after the famous Emperor Bonaparte saw the comet. This may be a coincidence, but there are other factors that make you wonder.
The previously described Comet Halley strangely affected the activity of such volcanoes as Ruiz (Colombia), Taal (Philippines), Katmai (Alaska). The impact of this comet was felt by people living near the Cossuin volcano (Nicaragua), which began one of the most destructive activities of the millennium.
Comet Encke caused a powerful eruption of the Krakatoa volcano. All this may depend on solar activity and the activity of comets, which provoke some nuclear reactions when approaching our planet.
Comet impacts are quite rare. However, some experts believe that the Tunguska meteorite belongs to just such bodies. They cite the following facts as arguments:
- A couple of days before the disaster, the appearance of dawns was observed, which, with their diversity, indicated an anomaly.
- The appearance of such a phenomenon as white nights in unusual places immediately after the fall of a celestial body.
- The absence of such an indicator of meteoricity as the presence of solid matter of a given configuration.
What a comet looks like - look at the video:
Comets of the Solar System are a fascinating topic that requires further study. Scientists around the world engaged in space exploration are trying to unravel the mysteries that these celestial bodies of amazing beauty and power carry.
The small nucleus of the comet 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, you can look into the deeper layers of the luminous gas and dust shell, but what remains will still be significantly larger in size than the true dimensions of the core. The central condensation visible in the comet's atmosphere visually and in photographs is called the photometric nucleus. It is believed that the comet’s nucleus itself is located in its center, that is, the center of mass is located. However, as shown by the Soviet astronomer D.O. Mokhnach, the center of mass may not coincide with the brightest region of the photometric core. This phenomenon is called the Mokhnach effect.
The hazy atmosphere surrounding the photometric core is called coma. The coma, together with the nucleus, makes up the head of the comet - a gas shell that is formed as a result of the heating of the nucleus as it approaches the Sun. Far from the Sun, the head looks symmetrical, but as it approaches it, it gradually becomes oval, then lengthens even more, and on the side opposite from the Sun, a tail develops from it, consisting of gas and dust that make up the head.
The nucleus is the most important part of a comet. However, there is still no consensus on what it actually is. Even in the time of Laplace, there was an opinion that the comet's nucleus was a solid body consisting of easily evaporating substances such as ice or snow, which quickly turned into gas under the influence of solar heat. This classic icy model of the cometary nucleus has been significantly expanded in recent times. The most widely accepted model is the core model developed by Whipple - a conglomerate of refractory rocky particles and frozen volatile components (methane, carbon dioxide, water, etc.). In such a core, ice layers of frozen gases alternate with dust layers. As the gases heat up, they evaporate and carry clouds of dust with them. This explains the formation of gas and dust tails in comets, as well as the ability of small nuclei to release gases.
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 evolution proceeds intensively through direct evaporation. The spectrum of such a comet is dominated by reflected sunlight, which makes it possible to spectrally distinguish “old” comets from “young” ones. Typically, comets with large orbital semi-axes are called “young”, since it is assumed that they are penetrating the inner regions of the Solar System for the first time. "Old" comets are comets with a short period of revolution around the Sun, which have passed their perihelion many times. In “old” comets, a refractory screen is formed on the surface, since during repeated returns to the Sun, the surface ice melts and becomes “contaminated.” This screen protects the ice underneath well from exposure to sunlight.
Whipple's model explains many cometary phenomena: abundant gas emission from small nuclei, the cause of non-gravitational forces that deflect the comet from the calculated path. The flows emanating from the core 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 presence of a monolithic core: one represents the core as a swarm of snowflakes, another as a cluster of rock and ice blocks, the third says that the core periodically condenses from particles of a meteor swarm under the influence of planetary gravity. Still, the Whipple model is considered the most plausible.
The masses of comet nuclei are currently determined extremely uncertainly, so we can talk about a probable range of masses: from several tons (microcomets) to several hundred, and possibly thousands of billions of tons (from 10 to 10-10 tons).
The comet's coma surrounds the nucleus in a hazy atmosphere. In most comets, the coma consists of three main parts, which differ markedly in their physical parameters:
the closest area adjacent to the nucleus is the internal, molecular, chemical and photochemical coma,
visible coma, or radical coma,
ultraviolet, or atomic coma.
At a distance of 1 AU. from the Sun, the average diameter of the internal coma is D = 10 km, visible D = 10-10 km and ultraviolet D = 10 km.
In the internal coma, the most intense physical and chemical processes occur: 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 influence of solar radiation continues, but less intensely than in an internal coma.
L.M. Shulman, based on the dynamic properties of matter, proposed dividing the cometary atmosphere into the following zones:
near-wall layer (area of evaporation and condensation of particles on the ice surface),
perinuclear region (region of gas-dynamic movement of matter),
transition region,
the region of free molecular expansion of cometary particles into interplanetary space.
But not every comet must have all the listed atmospheric regions.
As the comet approaches the Sun, the diameter of the visible head increases day by day; after passing the perihelion of its orbit, the head increases again and reaches its maximum size between the orbits of 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.
The heads of comets take on a variety of shapes as the comet moves around its orbit. Far 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 a chain line.
S.V. Orlov proposed the following classification of comet heads, taking into account their shape and internal structure:
Type E; - observed in comets with bright comas framed on the Sun's side by luminous parabolic shells, the focus of which lies in the comet's nucleus.
Type C; - observed in comets whose heads are four times weaker than type E heads and resemble an onion in appearance.
Type N; - observed in comets that lack both coma and shells.
Type Q; - observed in comets that have a weak protrusion towards the Sun, that is, an anomalous tail.
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 of a comet is its tail. The tails are almost always directed in the direction opposite to the Sun. Tails consist of dust, gas and ionized particles. Therefore, depending on the composition, the tail particles are repelled in the direction opposite to the Sun by forces emanating from the Sun.
F. Bessel, studying the shape of the tail of Halley's comet, 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 dividing them into three separate groups, depending on the magnitude of the repulsive acceleration.
Analysis of the spectrum of the head and tail showed the presence of the following atoms, molecules and dust particles:
Organic C, C, CCH, CN, CO, CS, HCN, CHCN.
Inorganic H, NH, NH, O, OH, HO.
Metals - Na, Ca, Cr, Co, Mn, Fe, Ni, Cu, V, Si.
Ions - CO, CO, CH, CN, N, OH, HO.
Dust - silicates (in the infrared region).
The mechanism of luminescence of cometary molecules was deciphered in 1911 by K. Schwarzschild and E. Krohn, who came to the conclusion that this is a mechanism of fluorescence, that is, re-emission of sunlight.
Sometimes quite unusual structures are observed in comets: rays emerging from the nucleus at different angles and collectively forming a radiant tail; halos - systems of expanding concentric rings; contracting shells - the appearance of several shells constantly moving towards the core; cloud formations; omega-shaped tail bends that appear during solar wind inhomogeneities.
There are also non-stationary processes in the heads of comets: flashes of brightness associated with increased short-wave radiation and corpuscular flows; separation of nuclei into secondary fragments.
Project Vega (Venus - Halley's Comet) was one of the most complex in the history of space exploration. It consisted of three parts: studying the atmosphere and surface of Venus using landers, studying the dynamics of the atmosphere of Venus using balloon probes, flying through the coma and plasma shell of Comet Halley.
The automatic station "Vega-1" launched from the Baikonur Cosmodrome on December 15, 1984, followed 6 days later by "Vega-2". In June 1985, they passed near Venus one after another, successfully conducting research related to this part of the project.
But the most interesting was the third part of the project - the study of Halley's Comet. For the first time, spacecraft had to “see” the comet’s nucleus, which was elusive to ground-based telescopes. Vega 1's encounter with the comet occurred on March 6, and Vega 2's encounter on March 9, 1986. They passed at a distance of 8900 and 8000 kilometers from its core.
The most important task in the project was to study the physical characteristics of the comet's nucleus. For the first time, the core was considered as a spatially resolved object, its structure, dimensions, infrared temperature were determined, and estimates of its composition and characteristics of the surface layer were obtained.
At that time, it was not yet technically possible to land on the comet's nucleus, since the speed of the encounter was too high - in the case of Halley's comet it was 78 km/s. It was dangerous even to fly too close, as comet dust could destroy the spacecraft. The flight distance was chosen taking into account the quantitative characteristics of the comet. Two approaches were used: remote measurements using optical instruments and direct measurements of matter (gas and dust) leaving the core and crossing the trajectory of the apparatus.
The optical instruments were placed on a special platform, developed and manufactured jointly with Czechoslovak specialists, which rotated during the flight and tracked the trajectory of the comet. With its help, three scientific experiments were carried out: television filming of the nucleus, measurement of the flux of infrared radiation from the nucleus (thereby determining the temperature of its surface) and the spectrum of infrared radiation of the internal “peri-nuclear” parts of the coma at wavelengths from 2.5 to 12 micrometers in order to determine it composition. IR radiation studies were carried out using an IR infrared spectrometer.
The results of optical research can be formulated as follows: the core is an elongated monolithic body of irregular shape, the dimensions of the major axis are 14 kilometers, and the diameter is about 7 kilometers. Every day, several million tons of water vapor leave it. Calculations show that such evaporation can come from an icy body. But at the same time, the instruments established that the surface of the core is black (reflectivity less than 5%) and hot (about 100 thousand degrees Celsius).
Measurements of the chemical composition of dust, gas and plasma along the flight path showed the presence of water vapor, atomic (hydrogen, oxygen, carbon) and molecular (carbon monoxide, carbon dioxide, hydroxyl, cyanogen, etc.) components, as well as metals with an admixture of silicates.
The project was implemented with broad international cooperation and with the participation of scientific organizations from many countries. As a result of the Vega expedition, scientists saw the cometary nucleus for the first time and received a large amount of data on its composition and physical characteristics. The rough diagram was replaced by a picture of a real natural object that had never been observed before.
NASA is currently preparing three large expeditions. The first of them is called “Stardust”. It involves the launch in 1999 of a spacecraft that will pass 150 kilometers from the nucleus of comet Wild 2 in January 2004. Its main task: to collect comet dust for further research using a unique substance called “aerogel”. The second project is called “Contour” (“COmet Nucleus TOUR”). The device will be launched in July 2002. In November 2003, it will encounter Comet Encke, in January 2006 - with Comet Schwassmann-Wachmann-3, and finally, in August 2008 - with Comet d'Arrest. It will be equipped with advanced technical equipment that will allow obtaining high-quality photographs nuclei in different spectra, as well as collect cometary gas and dust. The project is also interesting because the spacecraft, using the Earth’s gravitational field, can be reoriented in 2004-2008 to a new comet. The third project is the most interesting and complex. It is called “Deep”. Space 4" and is part of a research program called "NASA New Millennium Program". It is planned to land on the nucleus of the comet Tempel 1 in December 2005 and return to Earth in 2010. The spacecraft will explore the comet's nucleus, collect and deliver it to Earth. soil samples.
The most interesting events over the past few years have been: the appearance of Comet Hale-Bopp and the fall of Comet Schumacher-Levy 9 on Jupiter.
Comet Hale-Bopp appeared in the sky in the spring of 1997. Its period is 5900 years. There are some interesting facts associated with this comet. In the fall of 1996, American amateur astronomer Chuck Shramek transmitted to the Internet a photograph of a comet, in which a bright white object of unknown origin, slightly flattened horizontally, was clearly visible. Shramek called it a "Saturn-like object" (SLO for short). The size of the object was several times greater than the size of the Earth.
The reaction of official scientific representatives was strange. Sramek's image was declared a fake and the astronomer himself a hoaxer, but no clear explanation of the nature of SLO was offered. The image published on the Internet caused an explosion of occultism, a huge number of stories were spread about the coming end of the world, the “dead planet of an ancient civilization,” evil aliens preparing to take over the Earth with the help of a comet, even the expression: “What the hell is going on?” (“What the hell is going on?”) was paraphrased in “What the Hale is going on?”... It is still not clear what kind of object it was, what its nature was.
Preliminary analysis showed that the second “core” was a star in the background, but subsequent images refuted this assumption. Over time, the “eyes” connected again, and the comet took on its original appearance. This phenomenon has also not been explained by any scientist.
Thus, comet Hale-Bopp was not a standard phenomenon; it gave scientists a new reason to think.
Another sensational event was the fall of the short-period comet Schumacher-Levy 9 onto Jupiter in July 1994. The comet's nucleus in July 1992, as a result of its approach to Jupiter, split into fragments, which subsequently collided with the giant planet. Due to the fact that the collisions occurred on the night side of Jupiter, terrestrial researchers could only observe flashes reflected by the planet’s satellites. The analysis showed that the diameter of the fragments is from one to several kilometers. 20 comet fragments fell on Jupiter.
Scientists say that the breakup of a comet into pieces is a rare event, the capture of a comet by Jupiter is an even rarer event, and the collision of a large comet with a planet is an extraordinary cosmic event.
Recently, in an American laboratory, on one of the most powerful Intel Teraflop computers with a performance of 1 trillion operations per second, a model of the fall of a comet with a radius of 1 kilometer to the Earth was calculated. The calculations took 48 hours. They showed that such a cataclysm would be fatal for humanity: hundreds of tons of dust would rise into the air, blocking access to sunlight and heat, a giant tsunami would form when it fell into the ocean, destructive earthquakes would occur... According to one hypothesis, dinosaurs became extinct as a result of the fall of a large comet or asteroid. In Arizona, there is a crater with a diameter of 1219 meters, formed after the fall of a meteorite 60 meters in diameter. The explosion was equivalent to the explosion of 15 million tons of trinitrotoluene. It is assumed that the famous Tunguska meteorite of 1908 had a diameter of about 100 meters. Therefore, scientists are now working to create a system for early detection, destruction or deflection of large cosmic bodies flying close to our planet.
comet discovery destruction cosmic body
Comet(from ancient Greek. κομ?της , kom?t?s - “hairy, shaggy”) - a small icy celestial body moving in orbit in the Solar System, which partially evaporates when approaching the Sun, resulting in a diffuse shell of dust and gas, as well as one or more tails.The first appearance of a comet, which was recorded in the chronicles, dates back to 2296 BC. And this was done by a woman, the wife of Emperor Yao, who gave birth to a son who later became Emperor Ta-Yu, the founder of the Khia dynasty. It was from this moment that Chinese astronomers monitored 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 plotted 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 such a rare spectacle in the sky when a foggy body is visible 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 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 to study 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. Over 39 years of observations, Messier discovered 13 new comets! In the first half of the 19th century, Jean Pons especially distinguished himself among the “catchers” of comets. The caretaker 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 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. About 50 comets are available for observation. In 1861, the first photograph of a comet was taken. However, according to archival data, a record dated September 28, 1858 was discovered in the annals of Harvard University, in which Georg Bond reported an attempt to obtain a photographic image of the comet at the focus of a 15" refractor! At a shutter speed of 6", the brightest part of the coma measuring 15 arc seconds was worked out. The photograph has not been preserved.
The 1999 Comet Orbit Catalog contains 1,722 orbits for 1,688 cometary appearances from 1,036 different comets. From ancient times to the present day, about 2000 comets have been noticed and described. In the 300 years since 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 the orbit of Mercury to Jupiter and back in 3.3 years. The most distant of those observed twice is a comet discovered in 1788 by Caroline Herschel and returning 154 years later from a distance of 57 AU. In 1914, Comet Delavan set out to break the distance record. It will move away to 170,000 AU. and “finishes” after 24 million years.
So far, more than 400 short-period comets have been discovered. Of these, about 200 were observed during more than one perihelion passage. Many of them belong to so-called families. For example, approximately 50 of the shortest-period comets (their complete revolution around the Sun lasts 3-10 years) form the Jupiter family. Slightly smaller in number are 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 expressed by F. Whipple in 1949 that the nuclei of comets are something like “dirty snowballs” several kilometers across. They appear to consist of frozen water, carbon dioxide, methane and ammonia with dust and rocky matter frozen inside. As the 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. The coma can be up to a million kilometers across. The nucleus itself is too small to be seen directly. 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 produced by the decomposition of water molecules under the influence of solar radiation. In 1996, X-ray emission from comet Hyakutake was discovered, and subsequently it was discovered that other comets are sources of X-ray radiation.
Observations in 2001, carried out using the Subara telescope's high-dispersive spectrometer, allowed astronomers to measure for the first time the temperature of frozen ammonia in the comet's nucleus. Temperature value at 28 + 2 degrees Kelvin suggests that Comet LINEAR (C/1999 S4) formed between the orbits of Saturn and Uranus. This means that astronomers can now not only determine the conditions under which comets form, but also find where they originate. Using spectral analysis, organic molecules and particles were discovered 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, in most cases, are “fragments” of more complex parent molecules and molecular complexes. The nature of the origin of parent molecules in cometary nuclei has not yet been solved. So far it is only clear that these are very complex molecules and compounds such as 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 atmosphere or on the surface of planets with sufficiently stable and favorable conditions.
