Fireballs and meteorites. Everything you wanted to know about meteorites, asteroids and comets What is a comet asteroid meteorite
Years in Chelyabinsk led to many questions.
According to the data, a meteorite with a diameter of about 15 meters and weighing 7,000 tons entered the atmosphere at an angle of about 20 degrees at a speed of 65,000 km per hour. It passed through the atmosphere for 30 seconds and then shattered. This led to an explosion at an altitude of about 20 km above the ground, producing a shock wave with a power of 300 kilotons. As a result, more than 1000 people were injured.
Fragments of a meteorite were recently found near Lake Chebarkul.
Events such as a meteorite fall once again remind us of the potential danger that lies in outer space. What is a meteorite, an asteroid and a comet? How often do such events happen and can they be prevented?
Meteor falling
Meteor, meteorite, meteoroid - what's the difference?
A meteor is the scientific name for a "shooting star" and it is a luminous trail from space debris that end up in the Earth's atmosphere. They can be as small as a grain of sand and large meteoroids up to 10-30 meters in size. As a rule, they burn up in the atmosphere, and those that fall to Earth are called meteorites.
How often does a meteorite fall to Earth?
Small drops happen every few months, but we don't see them. The thing is that two-thirds of the Earth is oceans, so we often miss these events. Objects as large as the one that exploded in Chelyabinsk are much less common, about every five years. So in 2008, a similar event was observed in Sudan, but no one was hurt.
Meteorite flies to Earth: can it be prevented?
As a rule, such meteoric bodies go unnoticed, as most telescopes are aimed at detecting huge, potentially dangerous asteroids. So far, there is no weapon capable of preventing the fall of a meteorite or asteroid.
Falling asteroid
The Chelyabinsk meteorite was the largest after the 1908 Tunguska meteorite in Siberia, which was caused by an object about the size of asteroid 2012 DA14, which flew safely at a minimum distance of 27,000 km from Earth on February 15, 2013.
Asteroid walkthrough: What is an asteroid?
An asteroid is a celestial body that orbits the sun, usually between Mars and Jupiter. Asteroids are also called space debris or debris left over from the formation of the solar system.
Due to collisions, some asteroids are ejected from the main belt, and they find themselves on a trajectory that crosses the Earth's orbit.
Large asteroids are called planetodids, and objects less than 30 meters are called meteoroids.
The size of asteroids: how big can they be?
Asteroid 2012 DA14, which flew by on Friday, was about 45 meters in diameter and about 130,000 tons in mass.... Scientists believe that there are about 500,000 asteroids the size of asteroid 2012 DA14. However, less than one percent of asteroids have been discovered so far.
The alleged asteroid that killed the dinosaurs 65 million years ago is believed to have a diameter of about 10-15 km. If an asteroid of this magnitude fell today, it would wipe out the entire modern civilization.
Statistically, asteroids over 50 meters fall to Earth once a century. Asteroids larger than 1 km in diameter can collide every 100 thousand years.
Fall comet
2013 can be called the year of comets, since we will be able to observe two of the brightest comets in history at once.
What is a comet?
Comets are the heavenly bodies of our solar system, made up of ice, dust and gas. Most of them are located in the Oort Cloud, a mysterious region of the outer edge of the solar system. Periodically, they pass close to the Sun and begin to evaporate. The solar wind turns this vapor into a huge tail.
Most comets are too far from the Sun and Earth to be seen with the naked eye. Bright comets appear every few years, even less often two comets appear at once in one year.
Comet 2013
Comet PANSTARRS
Comet PANSTARRS or C / 2011 L4 was discovered in June 2011 with the Pan-STARRS 1 telescope located at the summit of Haleakala in Hawaii. In March 2013, the comet will be closest to the Sun (45,000 km) and Earth (164 million km).
Although at the time of its discovery, Comet PANSTARRS was a faint and distant object, it has become steadily brighter since then.
Comet ISON, discovered in 2012
When can you observe? Mid November - December 2013
Comet ISON or C / 2012 S1 was discovered on September 21, 2012 by two astronomers Vitaly Nevsky and Artem Novichonok using a telescope International Scientific Optical Network(ISON).
Orbital calculations have shown that ISON will come closest to the Sun at a distance of 1.2 million km. The comet will be bright enough to be seen in the sky as it approaches the Sun in the first weeks of November.
It is believed that this comet will be brighter than the full moon, and it will be visible even during the day.
Comet collision
Could a comet collide with Earth? It is known from history that the comet Shoemaker-Levy 9 collided with Jupiter in July 1994 and it became the first comet collision observed by scientists... Considering that this happened on an uninhabited planet, the event was rather an interesting example of the destructive forces of the universe. However, if this happened on Earth, history would take a completely different turn.
Comets and asteroids
Comets differ from asteroids in their unusual elongated elliptical orbits, that is, they move very far from the Sun. On the contrary, asteroids remain within the asteroid belt.
Fortunately, it takes many years to orbit a comet. The comet's approach to Earth occurs once every 200,000 years.... To date, it is unknown about comets that pose a threat to our planet in the near future.
Comets with orbital periods of more than 200,000 years have less predictable orbits and, while there is little chance of colliding with Earth, they should not be forgotten.
Asteroids, comets, meteors, meteorites are astronomical objects that seem identical to the uninitiated in the foundations of the science of celestial bodies. In fact, they differ in several ways. The properties that characterize asteroids and comets are easy to remember. They also have a certain similarity: such objects are classified as small bodies, often classified as space debris. What a meteor is, how it differs from an asteroid or comet, what are their properties and origin, and will be discussed below.
Tailed Wanderers
Comets are space objects consisting of frozen gases and stone. They originate in remote regions of the solar system. Modern scientists suggest that the main sources of comets are the interconnected Kuiper belt and the scattered disk, as well as hypothetically existing
Comets have highly elongated orbits. When approaching the sun, they form a coma and a tail. These elements consist of evaporating gaseous substances (ammonia, methane), dust and stones. The head of a comet, or coma, is a shell of the smallest particles, distinguished by its brightness and visibility. It has a spherical shape and reaches its maximum size when approaching the Sun at a distance of 1.5-2 astronomical units.
In front of the coma is the comet's nucleus. It usually has a relatively small size and elongated shape. At a considerable distance from the Sun, the core is all that remains of the comet. It consists of frozen gases and rocks.
Comet types
The classification of these is based on the frequency of their revolution around the star. Comets orbiting the Sun in less than 200 years are called short-period comets. Most often, they enter the inner regions of our planetary system from the Kuiper belt or the scattered disk. Long-period comets revolve with a period of more than 200 years. Their "homeland" is the Oort cloud.
"Minor planets"
Asteroids are composed of solid rocks. In terms of their size, they are much inferior to the planets, although some representatives of these space objects have satellites. Most of the minor planets, as they were called before, are concentrated in the Main, located between the orbits of Mars and Jupiter.
The total number of such cosmic bodies known in 2015 exceeded 670 thousand. Despite such an impressive number, the contribution of asteroids to the mass of all objects in the solar system is insignificant - only 3-3.6 * 10 21 kg. This is only 4% of the corresponding parameter of the Moon.
Not all small bodies are classified as asteroids. The selection criterion is diameter. If it exceeds 30 m, then the object is classified as an asteroid. Bodies with smaller dimensions are called meteoroids.
Asteroid classification
The grouping of these cosmic bodies is based on several parameters. Asteroids are united by the features of their orbits and the spectrum of visible light that has been reflected from their surface.
According to the second criterion, there are three main classes:
- carbon (C);
- silicate (S);
- metal (M).
The first category includes about 75% of all known asteroids today. With the improvement of equipment and more detailed research of such objects, the classification expands.
Meteoroids
A meteoroid is another type of cosmic body. They are not asteroids, comets, meteors or meteorites. The peculiarity of these objects is their small size. In terms of size, meteoroids are located between asteroids and cosmic dust. Thus, they include bodies with a diameter of less than 30 m. Some scientists define a meteoroid as a solid body with a diameter of 100 microns to 10 m. By their origin, they are primary or secondary, that is, formed after the destruction of larger objects.
When it enters the Earth's atmosphere, the meteoroid begins to glow. And here we are already approaching the answer to the question of what a meteor is.
Falling star
Sometimes, among the twinkling luminaries in the night sky, one suddenly flares up, describes a small arc and disappears. Whoever has seen such a thing at least once knows what a meteor is. These are "shooting stars" that have nothing to do with real stars. A meteor is actually an atmospheric phenomenon that occurs when small objects (the very meteoroids) hit the air envelope of our planet. The observed brightness of the flare directly depends on the initial dimensions of the cosmic body. If the brightness of a meteor exceeds the fifth it is called a fireball.
Observation
Such phenomena can only be admired from planets with an atmosphere. Meteors on the Moon or Mercury cannot be observed, since they have no air envelope.
Under the right conditions, "shooting stars" can be seen every night. It is best to admire the meteors in good weather and at a considerable distance from a more or less powerful source of artificial lighting. Also, there should be no moon in the sky. In this case, it will be possible to notice up to 5 meteors per hour with the naked eye. The objects that give rise to these single "shooting stars" revolve around the Sun in a variety of orbits. Therefore, it is impossible to accurately predict the place and time of their appearance in the sky.
Streams
Meteors, photos of which are also presented in the article, usually have a slightly different origin. They are part of one of several swarms of small cosmic bodies revolving around the star along a certain trajectory. In their case, the ideal period for observation (the time when, by looking at the sky, anyone can quickly understand what a meteor is) is pretty well defined.
A swarm of such space objects is also called a meteor shower. Most often, they are formed when the comet nucleus is destroyed. Individual swarm particles move parallel to each other. However, from the surface of the Earth, they appear to be flying out of a certain small region of the sky. This area is usually called the radiant of the stream. The name of a meteor swarm is usually given by the constellation in which its visual center (radiant) is located, or by the name of the comet, the disintegration of which led to its appearance.
Meteors, photos of which are easy to obtain with special equipment, belong to such large streams as the Perseids, Quadrantids, eta-Aquarids, Lyrids, Geminids. In total, the existence of 64 streams has been recognized to date, and about 300 more are awaiting confirmation.
Heavenly Stones
Meteorites, asteroids, meteors and comets are related concepts according to one criterion or another. The first are space objects that have fallen to Earth. Most often, their source is asteroids, less often comets. Meteorites carry invaluable data on various corners of the solar system outside the Earth.
Most of these bodies that hit our planet are very small in size. The most impressive meteorites in their dimensions leave traces after impact, which are quite noticeable even after millions of years. A well-known crater near the town of Winslow, Arizona. The fall of a meteorite in 1908 was supposedly the cause of the Tunguska phenomenon.
Such large objects "visit" the Earth every few million years. Most of the found meteorites are rather modest in size, but at the same time they do not become less valuable for science.
According to scientists, such objects can tell a lot about the time of the formation of the solar system. Presumably, they carry particles of the substance of which the young planets consisted. Some meteorites come to us from Mars or the Moon. Such space wanderers allow you to learn something new about neighboring objects without huge costs for distant expeditions.
To remember the differences between the objects described in the article, you can summarize the transformation of such bodies in space. An asteroid, consisting of solid rock, or a comet, which is a block of ice, when destroyed, generate meteoroids, which, when entering the planet's atmosphere, flare up as meteors, burn up in it or fall, turning into meteorites. The latter enrich our knowledge of all the previous ones.
Meteorites, comets, meteors, as well as asteroids and meteoroids are participants in continuous space movement. The study of these objects contributes greatly to our understanding of the structure of the universe. With the improvement of the equipment, astrophysicists receive more and more data on such objects. The mission of the Rosetta probe, completed relatively recently, unambiguously demonstrated how much information can be obtained from a detailed study of such cosmic bodies.
Asteroids.
Meteorites.
Meteora.
Omsk 2009
1. Asteroid
Definitions …………………………………………………… 3 Asteroids in the Solar System ………………………… .3 Study of asteroids …………………………… ………… .3 Naming of asteroids …………………………………… .4
Asteroid belt ………………………………………… ..5
Dimensions and material composition ………………………… ..5
The brightest asteroid …………………………………… ..6
2. METEORITE
Fall of meteorites ……………………………………… ..8
Types of meteorites ………………………………………… ... 9
Parent bodies of meteorites …………………………… .10
Frequency of occurrence ………………………………………… .11
Meteor observation ……………………………………… 11
Speed and height ………………………………………… ..11
Orbits ……………………………………………………… 12
Meteor showers ……………………………………. …… 12
Fireballs ……………………………………………………… 13
Physical processes ……………………………………… 14
Meteorite hazard ………………………………….… 14
Asteroid
ASTEROID- a small planet-like celestial body of the solar system, orbiting the sun. Asteroids, also known as minor planets, are significantly smaller than the planets.
Definitions.
Term asteroid(from ancient Greek - "like a star") was introduced by William Herschel on the basis that these objects when observed through a telescope looked like points of stars - in contrast to planets, which look like disks when viewed through a telescope. The exact definition of the term "asteroid" is still not established. The term "minor planet" (or "planetoid") is not suitable for defining asteroids, as it also indicates the location of an object in the solar system. However, not all asteroids are minor planets.
One way to classify asteroids is to measure their size. The current classification defines asteroids as objects with a diameter of more than 50 m, separating them from meteoric bodies, which look like large stones, or may be even smaller. The classification is based on the statement that asteroids can survive upon entering the Earth's atmosphere and reach its surface, while meteors tend to completely burn up in the atmosphere.
As a result, an "asteroid" can be defined as a solid material object in the solar system that is larger than a meteor.
Asteroids in the solar system
At the moment, tens of thousands of asteroids have been discovered in the solar system. As of September 26, 2006, there were 385,083 objects in the databases, 164612 have precisely defined orbits and an official number assigned to them. 14,077 of them at that time had officially approved names. It is assumed that the solar system may contain from 1.1 to 1.9 million objects, measuring more than 1 km. Most of the currently known asteroids are concentrated within the asteroid belt located between the orbits of Mars and Jupiter.
Ceres was considered the largest asteroid in the solar system, measuring approximately 975 × 909 km, but since August 24, 2006 it has received the status of a dwarf planet. The other two largest asteroids, Pallas 2 and Vesta 4, have a diameter of ~ 500 km. 4 Vesta is the only object in the asteroid belt that can be observed with the naked eye. Asteroids moving in different orbits can also be observed during their transit near the Earth (eg 99942 Apophis).
The total mass of all asteroids in the main belt is estimated at 3.0-3.6 × 1021 kg, which is only about 4% of the mass of the Moon. The mass of Ceres is 0.95 × 1021 kg, that is, about 32% of the total, and together with the three largest asteroids 4 Vesta (9%), 2 Pallas (7%), 10 Hygea (3%) - 51%, that is, the absolute majority asteroids have an insignificant mass.
Study of asteroids
The study of asteroids began after the discovery of the planet Uranus in 1781 by William Herschel. Its average heliocentric distance turned out to be consistent with the Titius-Bode rule.
At the end of the 18th century, Franz Xaver von Zach organized a group of 24 astronomers. Since 1789, this group has been searching for a planet, which, according to the Titius-Bode rule, was supposed to be at a distance of about 2.8 astronomical units from the Sun - between the orbits of Mars and Jupiter. The task was to describe the coordinates of all stars in the region of the zodiacal constellations at a certain moment. On subsequent nights, the coordinates were checked, and objects were highlighted that moved a greater distance. The estimated displacement of the target planet should have been about 30 arc seconds per hour, which should be easily seen.
Ironically, the first asteroid, 1 Ceres, was discovered by the Italian Piazzi, who was not involved in this project, by chance, in 1801, on the very first night of the century. Three others - 2 Pallas, 3 Juno and 4 Vesta - were discovered in the next few years - the last one, Vesta, in 1807. After another 8 years of fruitless searches, most astronomers decided that there was nothing else there, and stopped research.
However, Karl Ludwig Henke persisted, and in 1830 resumed the search for new asteroids. Five years later, he discovered Astrea, the first new asteroid in 38 years. He also discovered Gebu less than two years later. After that, other astronomers joined in the search, and then at least one new asteroid was discovered per year (with the exception of 1945).
In 1891, Max Wolf first used astrophotography to search for asteroids, in which asteroids left short light lines in photographs with a long exposure period. This method has significantly increased the number of detections compared to previously used methods of visual observation: Wolf single-handedly discovered 248 asteroids, starting with 323 Brucius, while just over 300 were discovered before him. Now, a century later, only a few thousand asteroids are identified, numbered and named. Many more are known, but scientists are not very worried about studying them, calling the asteroids "space rabble" ("vermin of the skies").
Asteroid naming
At first, the asteroids were given the names of the heroes of Roman and Greek mythology, later the discoverers got the right to call it whatever they like, for example, by their own name. At first, asteroids were given predominantly female names, male names were given only to asteroids with unusual orbits (for example, Icarus, approaching the Sun closer to Mercury). Later, this rule also ceased to be observed.
Not any asteroid can get a name, but only one whose orbit is more or less reliably calculated. There have been cases when an asteroid received a name decades after its discovery. Until the orbit is calculated, the asteroid is given a serial number reflecting the date of its discovery, for example, 1950 DA. The numbers indicate the year, the first letter is the number of the crescent in the year in which the asteroid was discovered (in the given example, this is the second half of February). The second letter denotes the ordinal number of the asteroid in the indicated crescent; in our example, the asteroid was discovered first. Since there are 24 crescents, and 26 English letters, two letters are not used in the designation: I (due to the similarity with the unit) and Z. If the number of asteroids discovered during the crescent exceeds 24, they again return to the beginning of the alphabet, attributing the second letter index 2, next return 3, and so on.
After receiving the name, the official naming of the asteroid consists of a number (serial number) and a name - 1 Ceres, 8 Flora, etc.
Asteroid belt
The orbits of most numbered minor planets (98%) are located between the orbits of the planets Mars and Jupiter. Their average distances from the Sun range from 2.2 to 3.6 AU. They form the so-called main asteroid belt. All small planets, like large ones, move in a forward direction. The periods of their revolution around the Sun are, depending on the distance, from three to nine years. It is easy to calculate that the linear velocity is approximately 20 km / s. The orbits of many minor planets are noticeably elongated. The eccentricities rarely exceed 0.4, but, for example, for asteroid 2212 Hephaestus it is 0.8. Most of the orbits are located close to the plane of the ecliptic, i.e. to the plane of the Earth's orbit. Slopes are usually a few degrees, but there are exceptions. So, the orbit of Ceres has an inclination of 35 °, and large inclinations are known.
Perhaps, for us inhabitants of the Earth, it is most important to know the asteroids, the orbits of which are close to the orbit of our planet. There are usually three families of near-Earth asteroids. They are named after typical representatives - minor planets: 1221 Cupid, 1862 Apollo, 2962 Aton. The Amur family includes asteroids whose orbits at perihelion almost touch the Earth's orbit. The Apollonians cross the Earth's orbit from the outside, their superhelium distance is less than 1 AU. "Atons" have orbits with a semi-major axis less than the earth's and cross the earth's orbit from the inside. Representatives of all these families can meet with the Earth. As for close passages, they happen quite often.
For example, the asteroid Amur at the time of its discovery was 16.5 million kilometers from Earth, 2101 Adonis approached 1.5 million kilometers, 2340 Hathor - 1.2 million kilometers. Astronomers of many observatories observed the passage of the asteroid 4179 Tautatis past the Earth. On December 8, 1992, he was at a distance of 3.6 million kilometers from us.
Most of the asteroids are concentrated in the main belt, but there are important exceptions. Long before the discovery of the first asteroid, the French mathematician Joseph Louis Lagrange studied the so-called three-body problem, i.e. investigated how three bodies move under the influence of gravitational forces. The problem is very complex and has not yet been solved in general terms. However, Lagrange managed to find that in the system of three gravitating bodies (the Sun - the planet - a small body) there are five points where the movement of a small body turns out to be stable. Two of these points are in the orbit of the planet, forming equilateral triangles with it and the Sun.
Many years later, already in the XX century, theoretical constructions were embodied in reality. Near the Lagrangian points in the orbit of Jupiter, about two dozen asteroids were discovered, which were given the names of the heroes of the Trojan War. Asteroids - "Greeks" (Achilles, Ajax, Odysseus, etc.) are ahead of Jupiter by 60 °, the "Trojans" follow at the same distance behind. According to estimates, the number of asteroids near the Lagrange points can reach several hundred.
Dimensions and material composition
To find out the size of an astronomical object (if the distance to it is known), it is necessary to measure the angle at which it is seen from the Earth. However, it is no coincidence that asteroids are called minor planets. Even in large telescopes under excellent atmospheric conditions, using very complex, laborious techniques, it is possible to obtain rather indistinct outlines of the disks of only a few of the largest asteroids. The photometric method turned out to be much more effective. There are very accurate instruments for measuring gloss, i.e. the magnitude of the celestial body. In addition, the illumination created by the Sun on an asteroid is well known. All other things being equal, the brightness of an asteroid is determined by the area of its disk. It is necessary, however, to know what proportion of light is reflected by a given surface. This reflectivity is called albedo. Methods have been developed for its determination from the polarization of the light of asteroids, as well as the difference in brightness in the visible region of the spectrum and in the infrared range. As a result of measurements and calculations, the following sizes of the largest asteroids were obtained.
It is believed that there are three dozen asteroids with diameters of more than 200 km. Almost all of them are probably known. There are probably about 800 small planets with diameters from 80 to 200 km. With decreasing size, the number of asteroids increases rapidly. Photometric studies have shown that asteroids differ greatly in the degree of blackness of the substance that composes their surface. 52 Europe in particular has an albedo of 0.03. This corresponds to a dark substance similar in color to soot. Such dark asteroids are conventionally called carbonaceous (class C). Asteroids of another class are conventionally referred to as stony (S), since they seem to resemble the deep rocks of the Earth. The albedo of S-asteroids is much higher. For example, in 44 Niza it reaches 0.38. It is the lightest asteroid. The study of reflection spectra and polarimetry made it possible to distinguish another class - metallic, or M-asteroids. Probably, on their surface there are outcrops of metal, for example, nickel iron, as in some meteorites.
With the help of very sensitive photometers, periodic changes in the brightness of asteroids were investigated. The shape of the light curve can be used to judge the period of rotation of the asteroid and the position of the axis of rotation. The periods are very different - from several hours to hundreds of hours. The study of the light curve also allows one to draw certain conclusions about the shape of the asteroids. Most of them have an irregular, debris shape. Only the largest ones approach the ball.
The nature of the change in the brightness of some asteroids suggests that they have satellites. Some of the minor planets are possibly close binary systems or even bodies rolling over each other's surface.
But reliable information about asteroids can only be obtained from close-range observations - from spacecraft. This experience already exists. On October 29, 1991, the American spacecraft Galileo transmitted to Earth an image of the asteroid 951 Gaspra. The picture was taken from a distance of 16 thousand kilometers. The angularly smoothed shape of the asteroid and its cratered surface are clearly visible on it. You can confidently determine the size: 12x16 km.
For a long time, no asteroids were known whose orbits would lie entirely outside the orbit of Jupiter. But in 1977 it was possible to find such a small planet - it is 2060 Chiron. Observations have shown that its perihelion (the point of the orbit closest to the Sun) lies within the orbit of Saturn, and the aphelion (the point of greatest distance) - almost at the very orbit of Uranus, on the distant, cold and dark outskirts of the planetary system. The distance to Chiron at perihelion is 8.51 AU, and at aphelion - 18.9 AU. More distant asteroids were also discovered. It is assumed that they form the second, outer asteroid belt (Kuiper belt).
The brightest asteroid
The asteroid that appears to be the brightest from Earth is Vesta (4). When Vesta is at its minimum possible distance from Earth, its brightness reaches a magnitude of 6.5. In a very dark sky, Vesta can be detected even with the naked eye (this is the only asteroid that can be seen with the naked eye at all). The next brightest is the largest asteroid Ceres, but its brightness never exceeds the magnitude of 7.3. Although Vesta is three-fifths of the size of Ceres, it is much more reflective. Vesta reflects about 25% of the incident sunlight, while Ceres only 5%. Vesta appears to be light colored volcanic rocks that are highly reflective. Asteroids with this reflectivity belong to a separate class known as type E (the class designation comes from the name of the mineral enstatite). Such asteroids are rare, and their reflectivity ranges from 30 to 40%. The brightest of them - Nisa (44) - has a magnitude of 9.7, although its diameter is only 68 km.
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METEORITE
METEORITE- a piece of extraterrestrial matter that fell to the surface of the Earth; literally - "a stone from the sky".
Meteorites are the oldest known minerals (4.5 billion years old), so they should retain traces of the processes that accompanied the formation of planets. Until samples of lunar soil were delivered to Earth, meteorites remained the only samples of extraterrestrial matter. Geologists, chemists, physicists and metallurgists have been collecting and studying meteorites for over 200 years. From these studies, the science of meteorites arose. Although the first reports of falling meteorites appeared long ago, scientists were very skeptical about them. Various facts led them, in the end, to believe in the existence of meteorites. In 1800-1803, several prominent European chemists reported that the chemical composition of "meteor stones" from different fall sites was similar, but different from the composition of the earth's rocks. Finally, when in 1803 a terrible "stone rain" burst out in Aigle (France), strewn the ground with fragments and witnessed by many excited eyewitnesses, the French Academy of Sciences was forced to agree that these were indeed "stones from the sky." It is now believed that meteorites are fragments of asteroids and comets.
Meteorites are divided into "fallen" and "found". If a person saw a meteorite fall through the atmosphere and then actually found it on earth (a rare event), then such a meteorite is called "fallen." If it was found by chance and identified, which is typical of iron meteorites, then it is called "found." Meteorites are named after the places where they were found. In some cases, not one, but several fragments are found. For example, after the 1912 meteor shower in Holbrook, Arizona, more than 20,000 fragments were collected.
Falling meteorites. Until the meteorite reaches Earth, it is called a meteoroid. Meteoroids fly into the atmosphere at speeds from 11 to 30 km / s. At an altitude of about 100 km, due to friction against the air, the meteoroid begins to heat up; its surface is heated, and a layer several millimeters thick melts and evaporates. At this time, it can be seen as a bright meteor ( cm... METEOR). The molten and vaporized substance is continuously carried away by the pressure of air - this is called ablation. Sometimes, under the pressure of air, a meteor is crushed into many fragments. Passing through the atmosphere, it loses from 10 to 90% of its initial mass. Nevertheless, the interior of the meteor usually remains cold, since it does not have time to warm up in the 10 seconds that the fall lasts. Overcoming air resistance, small meteorites by the time they hit the ground significantly reduce their flight speed and go deeper into the ground, usually no more than a meter, and sometimes just remain on the surface. Large meteorites are slowed down slightly and upon impact produce an explosion with the formation of a crater, such as in Arizona or on the Moon. The largest of the found meteorites is considered to be the iron meteorite Goba (South Africa), the weight of which is estimated at 60 tons. It has never been moved from the place where it was found.
Each year, several meteorites are picked up immediately after their observed fall. In addition, more and more old meteorites are being discovered. In two places in the east of the piece. New Mexico, where the wind constantly blows the soil, has been found 90 meteorites. Hundreds of meteorites have been found on the surface of evaporating glaciers in Antarctica. Recently fallen meteorites are covered with a vitrified sintered crust that is darker than the interior. Meteorites are of great scientific interest; most major science museums and many universities have meteorite specialists.
METEORITE, possibly from Mars. Discovered in Antarctica 1984.
Types of meteorites. There are meteorites from various substances. Some are mainly composed of an alloy of iron and nickel containing up to 40% nickel. Among the fallen meteorites, only 5.7% are iron, but their share in the collections is much higher, since they are destroyed more slowly under the influence of water and wind, and besides, they are easier to detect by their appearance. If a section of an iron meteorite is polished and lightly etched with acid, it is often possible to see a crystal pattern of intersecting stripes, formed by alloys with different nickel contents, on it. This drawing is called "Widmanstätten figures" in honor of A. Widmanstetten (1754-1849), who first observed them in 1808.
The HENBURY IRON METEORITE (Australia) is a typical metallic type meteorite, many of which are rich in compounds found in iron ores.
Stone meteorites are divided into two large groups: chondrites and achondrites. The most common are chondrites, accounting for 84.8% of all fallen meteorites. They contain round grains of millimeter size - chondrules; some of the meteorites are composed almost entirely of chondrules. Chondrules have not been found in terrestrial rocks, but glassy grains of similar size have been found in lunar soil. Chemists have studied them carefully, since the chemical composition of chondrules is probably the primary matter of the solar system. This standard composition is called the "cosmic abundance of elements." In chondrites of a certain type, containing up to 3% carbon and 20% water, they strenuously searched for signs of biological matter, but they did not find any signs of living organisms either in these or in other meteorites. Achondrites are devoid of chondrules and resemble lunar rock in appearance.
METEORIT-AHONDRIT
METEORIT-CHONDRIT
Parent bodies of meteorites. The study of the mineralogical, chemical and isotopic composition of meteorites has shown that they are fragments of larger objects in the solar system. The maximum radius of these parent bodies is estimated at 200 km. The largest asteroids have about this size. The estimate is based on the cooling rate of the iron meteorite, which produces two alloys with nickel, forming Widmanstätten figures. Stony meteorites were probably knocked out of the surface of small planets, devoid of atmosphere and covered with craters like the Moon. Cosmic radiation destroyed the surface of these meteorites in the same way as moon rocks. However, the chemical composition of meteorites and lunar samples is so different that it is clear that the meteorites did not come from the moon. Scientists were able to photograph two meteorites in the process of falling and calculate their orbits from the photographs: it turned out that these bodies came from the asteroid belt. It is likely that asteroids are the main sources of meteorites, although some of them may be particles of evaporated comets.
METEOR
METEOR. The word "meteor" in Greek was used to describe various atmospheric phenomena, but now it refers to the phenomena that occur when particulate matter from outer space enters the upper atmosphere. In a narrow sense, a "meteor" is a luminous strip along the path of a decaying particle. However, in everyday life this word often denotes the particle itself, although scientifically it is called a meteoroid. If part of a meteoroid reaches the surface, then it is called a meteorite. People call meteors "shooting stars". Very bright meteors are called fireballs; sometimes this term denotes only meteoric events accompanied by sound phenomena.
The frequency of occurrence. The number of meteors that an observer can see over a given period of time is not constant. In good conditions, away from city lights and in the absence of bright moonlight, an observer can spot 5-10 meteors per hour. For most meteors, the glow lasts about a second and looks fainter than the brightest stars. After midnight, meteors appear more often, since the observer at this time is located on the forward side of the Earth in the course of orbital motion, on which more particles fall. Each observer can see meteors in a radius of about 500 km around him. In total, hundreds of millions of meteors appear in the Earth's atmosphere per day. The total mass of particles entering the atmosphere is estimated at thousands of tons per day - an insignificant value in comparison with the mass of the Earth itself. Measurements from spacecraft show that about 100 tons of dust particles, too small to cause visible meteors, also fall on the Earth per day.
Observation of meteors. Visual observations provide a lot of statistical data on meteors, but special instruments are needed to accurately determine their brightness, altitude and flight speed. For nearly a century, astronomers have been using cameras to photograph meteor trails. A rotating shutter (shutter) in front of the camera lens makes the meteor trail look like a dashed line, which helps to accurately determine the time intervals. Typically 5 to 60 exposures per second are done with this shutter. If two observers, separated by a distance of tens of kilometers, simultaneously photograph the same meteor, then it is possible to accurately determine the flight altitude of the particle, the length of its trail and, in time intervals, the flight speed.
Since the 1940s, astronomers have been observing meteors using radar. The cosmic particles themselves are too small to register, but when they fly through the atmosphere, they leave a plasma trail that reflects radio waves. Unlike photography, radar is effective not only at night, but also during the day and in cloudy weather. The radar detects small meteoroids that are inaccessible to the camera. From photographs, the flight path is more accurately determined, and the radar allows you to accurately measure distance and speed.
Television equipment is also used to observe meteors. Electron-optical converters make it possible to register faint meteors. Cameras with CCDs are also used. In 1992, when recording a sporting event on a video camera, the flight of a bright fireball was recorded, ending with a meteorite falling.
Speed and height. The speed with which meteoroids fly into the atmosphere is in the range from 11 to 72 km / s. The first value is the speed acquired by the body only due to the attraction of the Earth. (The same speed must be obtained by a spacecraft in order to escape from the Earth's gravitational field.) A meteoroid arriving from distant regions of the Solar System, due to its attraction to the Sun, acquires a speed of 42 km / s near the Earth's orbit. The orbital speed of the Earth is about 30 km / s. If the meeting takes place "head-on", then their relative speed is 72 km / s. Any particle arriving from interstellar space must have an even greater speed. The absence of such fast particles proves that all meteoroids are members of the solar system.
A BRIGHT METEOR from the Perseid stream.
The height at which a meteor begins to glow or is detected by radar depends on the particle's entry speed. For fast meteoroids, this height can exceed 110 km, and the particle is completely destroyed at an altitude of about 80 km. In slow meteoroids, this occurs lower, where the air density is greater. Meteors, comparable in brightness to the brightest stars, are formed by particles with a mass of tenths of a gram. Larger meteoroids usually take longer to disintegrate and reach lower altitudes. They
Asteroids are solid rocky bodies that, like planets, move in near-solar elliptical orbits. But the dimensions of these bodies are much smaller than those of ordinary planets, therefore they are also called minor planets. The diameters of asteroids range from several tens of meters (conventionally) to 1000 km (the size of the largest asteroid Ceres). The term "asteroid" (or "star-like") was coined by the famous 18th century astronomer William Herschel to characterize the appearance of these objects when observed through a telescope. Even with the largest ground-based telescopes, it is impossible to distinguish the visible disks of the largest asteroids. They are observed as point light sources, although, like other planets, they themselves do not emit anything in the visible range, but only reflect the incident sunlight.
In total, about 20,000 asteroids have been discovered to date, of which about 10,000 have been registered, that is, they have been assigned numbers or even proper names, and the orbits have been calculated with great accuracy. The names of the asteroids are usually assigned by their discoverers, but in accordance with the established international rules. In the beginning, when little was known about the minor planets, their names were taken, as for other planets, from ancient Greek mythology. The annular region of space that these bodies occupy is called the main asteroid belt. At an average speed of about 20 km / s, the asteroids of the main belt spend 3 to 9 Earth years for one revolution around the Sun, depending on the distance from it.
Information about some asteroids.
1 Ceres is the largest asteroid to be discovered first. It was discovered by the Italian astronomer Giuseppe Piazzi on January 1, 1801, and is named after the Roman goddess of fertility.
2 Pallas is the second largest asteroid, also the second discovered. This was done by the German astronomer Heinrich Olbers on March 28, 1802.
3 Juno - discovered by K. Harding in 1804.
4 Vesta is the third largest asteroid, also discovered by G. Olbers in 1807. This body has observational signs of the presence of basaltic crust covering the olivine mantle, which may be a consequence of the melting and differentiation of its matter. The image of the visible disk of this asteroid was first obtained in 1995 using the American Space Telescope. Hubble operating in low-earth orbit.
8 Flora is the largest asteroid in the large asteroid family of the same name, numbering several hundred members, which was first characterized by the Japanese astronomer K. Hirayama. Asteroids of this family have very close orbits, which probably confirms their joint origin from a common parent body destroyed in a collision with some other body.
243 Ida is a main-belt asteroid, images of which were obtained by the Galileo spacecraft on August 28, 1993. These images allowed the discovery of a small satellite of Ida, later named Dactyl. (See Figures 2 and 3).
253 Matilda is an asteroid imaged by the NIAR spacecraft in June 1997 (See Fig. 4).
433 Eros is a near-Earth asteroid imaged by the NIAR spacecraft in February 1999.
951 Gaspra is a main-belt asteroid first imaged by the Galileo spacecraft on October 29, 1991 (See Fig. 1).
1566 Ikarus is an asteroid approaching the Earth and crossing its orbit with a very large orbital eccentricity (0.8268).
1620 Geographer - A near-Earth asteroid that is either a double object or has a very irregular shape. This follows from the dependence of its brightness on the phase of rotation around its own axis, as well as from its radar images.
1862 Apollo is the largest asteroid of the eponymous family of bodies approaching the Earth and crossing its orbit. The eccentricity of Apollo's orbit is large enough - 0.56.
2060 Chiron is an asteroid-comet that periodically exhibits cometary activity (regular increases in brightness near the perihelion of the orbit, that is, at a minimum distance from the Sun, which can be explained by the evaporation of volatile compounds that make up the asteroid), moving along an eccentric trajectory (eccentricity 0.3801) between the orbits of Saturn and Uranus.
4769 Castalia is a binary asteroid with approximately the same (0.75 km in diameter) components in contact. Its radio image was obtained by radar at Arecibo.
4179 Toutatis is a binary asteroid, the components of which are likely in contact and are approximately 2.5 km and 1.5 km in size. Images of this asteroid were obtained using radars located at Arecibo and Goldstone. Of all the currently known asteroids approaching the Earth in the 21st century, Toutatis should be at the closest distance (about 1.5 million km, September 29, 2004).
Asteroid Eros
Asteroid Phobos
Asteroid Gaspar
Asteroid Cercera
COMETS
Comets are celestial bodies, consisting of a "head" - a small bright clot-core, which is surrounded by a light foggy shell, consisting of gases and dust. In bright comets, as they approach the Sun, a "tail" is formed - a weak luminous strip, which, as a result of light pressure and the action of the solar wind, is most often directed in the opposite direction from our star.
As it approaches the Sun, the comet is heated by solar heat so that gas and dust fly away from the surface, forming a bright tail. Despite the fact that comets have been known since ancient times, their serious scientific research began only at the end of the 18th century, and the first reliable information about their mass, speed, orbital elements, and chemical composition became known to astronomers only in the 20th century. But with the accumulation of data on the structure of comets, more and more questions arose that modern science is not yet able to answer. One such question is the origin of comets. We do not currently know where comets come from or how comets are formed. There are two main assumptions about this:
According to the first, comets are born and come to us from some area located outside the boundaries of the solar system. According to the second assumption, comets are born in a hypothetical Oort cloud, located somewhere near the very borders of the solar system, possibly beyond the orbits of Uranus or Pluto.
Halley first predicted the appearance of a comet in 1758. Many years after his death, it did appear. It was named Halley's comet and was seen in 1835 and in 1910 and 1986.
Halley's comet
METEOR
A meteor is a celestial body that burns up when it enters the atmosphere. Short-term flashes that occur in the earth's atmosphere when rapidly moving tiny solid particles enter it are called meteors (sometimes meteors are incorrectly called "shooting stars"). Comparatively large particles can cause a very bright flash
Meteors can be seen on any clear night, and under favorable atmospheric conditions, even the naked eye can see 5-10 meteors per hour. Since these particles revolve around the Sun in arbitrary orbits, they can accidentally appear in the sky in the most unexpected places. In addition to individual particles, whole swarms of them move around the Sun. Many of them are generated by decaying or decaying comets. Each meteor swarm revolves around the Sun with a constant period, and many of them meet with the Earth at certain periods. During such periods, the number of meteors increases significantly, and then they talk about meteor showers.
METEORITES
Meteorite- a solid body of cosmic origin that fell to the surface of the Earth. Most of the found meteorites weigh from a few grams to several kilograms. A crater may form at the site of a meteorite.
The most ancient earth craters, which undoubtedly arose from the fall of meteorites, were called astroblemes, which in ancient Greek means "star wounds". Astroblemes are up to two billion years old and are therefore often buried under younger sediments. Their diameter reaches hundreds of kilometers. They are found on all continents of the Earth.
Meteorites are classified into three main classes: iron, iron-stone, and stone.
The most common point of view, according to which M. are debris minor planets.
Meterites range in size from a few mm up to several m and weigh, respectively, from shares G up to dozens T. The largest survivor of the rift is the Goba iron meteorite, found in South West Africa in 1920, weighing about 60 T. The second largest iron meteorite Cape York, found in Greenland in 1818, weighs 34 T. It is known about 35 M., the mass of each of which exceeds 1 T.
Meteor Rain
Meteor Rain(iron rain, stone rain, fiery rain) - multiple fallout of meteorites due to its destruction in the process of falling to the Earth.
On January 1, 1801, the Italian astronomer Giuseppe Piazzi in his telescope discovered a new celestial body that looked like a star. It and similar bodies, discovered later, were called asteroids, which means "starlike" (from the Greek words "aster" - a star, "oidos" - a view).
More than 5,000 asteroids have been discovered so far. Usually these are small, irregularly shaped celestial bodies with a diameter of one to several tens of kilometers.
Of course, asteroids are not stars. Like planets, they do not emit their own light and revolve around the Sun. Therefore, they are also called minor planets.
Asteroids are part of the solar system. Most of them move between the orbits of Mars and Jupiter.
The origin of the asteroids has not yet been fully elucidated. For a long time, scientists assumed that these are the remnants of a certain destroyed planet. But recent studies show that, most likely, these are the remnants of that "building material" from which all the planets of the solar system known to us were once formed.
Comets
These celestial bodies got their name from the Greek word cometes, which means hairy.
Not many natural phenomena scared people as much as the appearance of a bright comet. It was considered a harbinger of various troubles such as epidemics, famines, wars.
But gradually scientists accumulated knowledge about these unusual celestial bodies, and now it is known that they are part of the solar system. Comets move in elongated orbits, then approaching the Sun, then moving away from it.
The main part of the comet is the solid core. Its diameter usually ranges from 1 to 10 km. The core consists of ice, frozen gases and solid particles of some other substances.
As the comet approaches the Sun, the core heats up, and its substances begin to evaporate. A shell of gas forms around the core, and then a long tail appears. A comet's tail can stretch for millions of kilometers! It is always directed away from the Sun and consists of gases and fine dust. As the comet moves away from the Sun, its tail and gas envelope gradually disappear.
Over time, under the influence of solar heat, many comets are completely destroyed. Their particles are scattered in outer space.
Comets visible to the naked eye are rare.
But with the help of telescopes, scientists observe them quite often.
Meteora
A huge amount of so-called cosmic dust moves in interplanetary space. In most cases, these are the remnants of collapsed comets. From time to time they burst into the Earth and flare up, sweeping across the black sky with a bright luminous line: it seems
that a star is falling. These flashes of light are called meteors (from the Greek word for "meteoros" - soaring in the air).
Cosmic particles heat up as a result of friction against the atmosphere, flare up and burn. This usually happens at an altitude of 80-100 km above the Earth.
Meteorites
In addition to cosmic dust, larger bodies also move in interplanetary space, mainly debris of asteroids. Once in the Earth's atmosphere, they do not have time to burn up in it. Their remains fall on. Space bodies that have fallen to the Earth are called meteorites. Meteorites are divided into three large classes: stone, iron and iron-stone.
The fall of large meteorites on the Earth is a rather rare phenomenon. Usually their mass ranges from hundreds of grams to several kilograms. The largest meteorite found weighed over 60 tons.
Scientists are carefully studying these cosmic "aliens", as they make it possible to judge the composition of celestial bodies, the processes taking place in space.
Mysterious Neighbors of the Sun
The largest of the asteroids, Ceres, has a diameter of about 1000 km. He was the first to open. The total mass of all asteroids is about 20 times less than the mass of the Moon. Despite this, they pose some danger to our planet. Scientists do not exclude that any of the asteroids may collide with the Earth. This would lead to a terrible disaster. Ways to protect the Earth from this danger are now being developed.
The most famous comet, Halley's comet, approaches the Sun once every 76 years. At this time, it flies relatively close to the Earth, and it can be observed with the naked eye. The last time humans saw this comet was in 1986. Its next appearance is expected in 2062.
About 2000 meteorites fall to the Earth throughout the year. The fall of large meteorites is accompanied by an explosion. A meteorite crater forms at the site of the explosion. One of the largest meteorite craters is located in the United States (Arizona), its diameter is 1200 m, and its depth is almost 200 m.
- In which part of the solar system do most asteroids move?
- What is the structure of a comet? What does its core consist of?
- How does the appearance of a comet change during its orbit?
- What is a meteor; meteorite?
The solar system includes asteroids and comets. Space dust particles and larger bodies - asteroid fragments - move in interplanetary space. Flashes of light arising from the combustion of cosmic dust particles in the earth's atmosphere are called meteors, and space bodies that have fallen to the Earth are called meteorites.
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