(ORDO NEWS) — Man has been studying outer space for decades. And as it turned out, it can be by no means unsafe. When launching any aircraft into space, we must take into account their possible collision with asteroids. Yes, and being on Earth, a collision with them is also possible.
Asteroids are “small” pebbles, the size of which in some cases can exceed a car. Despite the fact that they are harmless on a galactic scale, such guests on Earth can lead to a local catastrophe. Fortunately, they often burn up in the atmosphere before reaching the Earth. And all the “flying” are known without a doubt. Scientists are interested in the asteroid, because on the tail they can bring news from distant solar systems, including about other life.
The emergence of the term
The word “asteriskos”, which later became “asteroid”, was introduced by the joint efforts of the English composer Charles Burney and the German astronomer William Herschel. From the ancient Greek language “asteroid” is translated as “similar to a star.” The fact is that, unlike the planets, which appear in the form of disks, asteroids, when observed through a telescope, looked exactly like stars – shining dots.
Until 2006, some dwarf planets like Ceres were also classified as asteroids.
Asteroids are celestial bodies that were formed due to the mutual attraction of dense gas and dust orbiting our Sun at an early stage of its formation. Some of these objects, like the asteroid Lutetia, have reached enough mass to form a molten core. At the moment Jupiter reaches its mass, most of the planetosimals (future protoplanets) were split and ejected from the original asteroid belt between Mars and Jupiter. During this epoch, part of the asteroids was formed due to the collision of massive bodies within the influence of the gravitational field of Jupiter.
Asteroids are classified according to such features as the visible spectrum of the reflection of sunlight and the characteristics of the orbits.
According to the characteristics of the orbits, asteroids are combined into groups, among which families can be distinguished. A group of asteroids is considered to be a certain number of such bodies whose orbital characteristics are similar, that is, semiaxis, eccentricity and orbital inclination. A family of asteroids should be considered a group of asteroids that do not just move in close orbits, but are probably fragments of one large body, and were formed as a result of its split.
The largest of the known families may contain several hundred asteroids, while the most compact families may contain up to ten. Approximately 34% of the bodies of the main asteroid belt are members of asteroid families.
As a result of the formation of most groups of asteroids in the solar system, their parent body was destroyed, but there are also groups whose parent body survived (for example, Vesta).
Classification by spectrum
The spectral classification is based on the spectrum of electromagnetic radiation, which is the result of the asteroid reflecting sunlight. Registration and processing of this spectrum makes it possible to study the composition of a celestial body and assign an asteroid to one of the following classes:
- Group of carbon asteroids or C-group. Representatives of this group consist mostly of carbon, as well as elements that were part of the protoplanetary disk of our solar system in the early stages of its formation. Hydrogen and helium, as well as other volatile elements, are practically absent in carbonaceous asteroids, however, the presence of various minerals is possible. Another distinguishing feature of such bodies is their low albedo – reflectivity, which requires the use of more powerful observation tools than in the study of asteroids of other groups. More than 75% of the asteroids in the solar system are representatives of the C-group. The most famous bodies of this group are Hygiea, Pallas, and once – Ceres.
- A group of silicon asteroids or S-group. Asteroids of this type are composed mainly of iron, magnesium and some other rocky minerals. For this reason, silicon asteroids are also called stony asteroids. Such bodies have a fairly high albedo, which allows you to observe some of them (for example, Irida) simply with binoculars. The number of silicon asteroids in the solar system is 17% of the total, and they are most common at a distance of up to 3 astronomical units from the Sun. The largest representatives of the S-group: Juno, Amphitrite and Herculina.
- Group of iron asteroids or X-group. The least studied group of asteroids, the abundance of which in the solar system is inferior to the other two spectral classes. The composition of such celestial bodies is not yet well understood, but it is known that most of them contain a high percentage of metals, sometimes nickel and iron. It is assumed that these asteroids are fragments of the nuclei of some protoplanets that formed in the early stages of the formation of the solar system. They can have both high and low albedo.
- Ceres is the largest asteroid in the asteroid belt. Since 2006, it has been considered a dwarf planet. It has a spherical shape, the crust consists of water ice and minerals, and the core is made of stone.
- Asteroid Pallas is rich in silicon, its diameter is 532 km.
- Asteroid Vesta – the heaviest asteroid has a diameter of 530 km. Heavy metal core, rocky bark.
- The Hygiea asteroid is the most common type of carbonaceous asteroid. Diameter 407 km.
- Asteroid Interamnia – refers to asteroids of rare spectral class F. Diameter 326 km.
- Asteroid Europpa – has an elongated orbit, a diameter of 302.5 km. Has a porous surface.
- Asteroid David – diameter from 270 to 326 km.
- Asteroid Sylvia – has at least two satellites. Its diameter is 232 km.
- Asteroid Hector – the size is 370 × 195 × 205 km with a shape similar to a peanut. Consists of rocks and ice.
- Asteroid Euphrosyne – size from 248 to 270 km.
Interesting facts about asteroids
- Not only asteroids fall to Earth. Every day more than 100 tons of material from asteroids and comets falls on our planet. Most of it is destroyed in the atmosphere due to friction. The surviving fragments are called meteorites;
- Asteroid impacts have been much more frequent in the past than they are today;
- The fall of the rock 65 million years ago led to the extermination of dinosaurs (influenced the development of terrestrial life);
- With a frequency of 2000 years, a rock the size of a football field falls to Earth;
- Once a year, rocks with the parameters of the machine arrive to us. As a result, you can watch a magnificent fireball. But the object most often burns out and does not have time to touch the surface;
- Asteroids are rich not only in water, but also in precious and useful metals;
- Some asteroids act as destroyed comets. Due to the approach to the Sun, the ice melts and only a rocky core remains;
- Some asteroids have their own satellites;
- Asteroids are also called minor planets and planetoids;
Sometimes asteroids are called minor planets. These are rocky remnants from the early solar system, formed 4.6 billion years ago. Most of the fragments are located between Mars and Jupiter. Asteroids can be huge (Vesta with a length of 530 km) and small (less than 10 m). The total mass of all asteroids in the solar system is inferior to the lunar one.
Most asteroids are irregular in shape, although some have managed to become almost spherical with crater formations. When rotating in elliptical orbits, asteroids also randomly fall. Approximately 150 objects have satellites (some even have two). There are binary asteroids, where two rocky bodies converge in size and rotate around a common center of mass.
There are 3 asteroid classes: C, S and M. Most often you can find C-type (chondrites), represented by clay and silicates, and in appearance they seem dark. These are one of the oldest objects in the system. S-type (stony) are composed of both silicates and nickel iron. And the M-type is metal. Differences in composition are based on distance from the Sun during formation. Some succumbed to temperature heating and partially melted.
The powerful gravity of Jupiter and impacts with other asteroids lead to a change in trajectories, which is why they are thrown out of their usual place of residence to other planets. In the past, many large objects crashed into the Earth, which helped bring new elements to the composition.
Scientists are constantly monitoring asteroids approaching our planet or crossing its orbital path. The minimum critical distance is 45 million km. Radar is a valuable tool. It reflects signals from objects and receives the necessary data: orbit, size, shape and concentration of metals.
Several missions were specially sent to the asteroids. In 1991, Galileo was sent to Gaspra and Ida. Matilda and Eros were followed by NEAR-Shoemaker. In 2008, Stein was visited by Rosetta, and in 2010 by Lutetia. Close flybys were made by Deep Space 1 and Stardust.
In 2005, the Hayabusa spacecraft landed on the asteroid Itokawa and attempted to take samples. In 2010, he delivered them to Earth. In 2007, the Dawn mission was launched. In 2012, the device headed for Ceres, where it arrived in 2015.
Name of asteroids
The IAU is not so strict about the asteroid naming system. That’s why we have the asteroid Spock, Frank Zappa, Columbus, etc. But for now it is forbidden to call them animal names. They also assign numeric values.
Astronomer on the structure of the substance of asteroids, their taxonomic types and sources of terrestrial life:
Types of asteroids
- Trojan asteroids;
- near-Earth asteroids;
- Interesting facts about asteroids;
- Classes of asteroids;
- Asteroid orbit;
- What is the difference between an asteroid and a comet;
- The largest asteroids;
- The largest asteroid in the solar system;
- Asteroid Apophis;
- Craters on Earth;
- The asteroid that killed the dinosaurs;
Asteroids in the solar system
Today it is known that there are 670 thousand asteroids in the solar system. For more than 400 thousand of them, orbits and an approved serial number have been determined. More than 19 thousand such objects have official names. Presumably in the solar system there may be up to 2 million objects with a diameter of more than one kilometer. Most of them are located between the orbits of Mars, Jupiter. Here is the so-called asteroid belt.
The asteroids Pallas and Vesta have a diameter of more than 500 kilometers. Vesta can be seen with the naked eye. The mass of the asteroid is about 950 quadrillion tons. Until 2006, Ceres was the largest asteroid. After this date, the object is classified as a so-called dwarf planet. The total mass of all considered celestial bodies exceeds 3 quintillion tons.
Chemical composition, shape and size of asteroids
The first attempts to determine the size and shape of asteroids were made at the beginning of the 19th century by German astronomers W. Herschel and I. Schroeter.
Modern astronomy uses the following methods for determining the size of asteroids:
- thermal radiometry.
The largest asteroids have a diameter exceeding 500 km. However, most of the objects of this class have a diameter from several hundred meters to several kilometers.
The shape of most asteroids is irregular. This is due to the fact that the negligible force of attraction cannot give them a spherical shape. Only the largest asteroids are spherical (unless similar bodies have collided with them).
The irregular shape of small objects is also confirmed by the fact that their brightness decreases in proportion to the increase in the phase angle.
The vast majority of asteroids are made up of carbon. Silicate and metallic bodies are less common. Metal objects (class M) contain cobalt and nickel. Rarely found basalt, olivine space bodies.
History of asteroid discoveries
The study of these objects of the solar system began after the discovery of the planet Uranus. In the late 18th century, a group of astronomers searched for a planet that was calculated to be between Mars and Jupiter. They also needed to calculate the coordinates of all the stars and constellations at a certain point in time. In the future, the coordinates were checked to easily find out their offset.
The first asteroid, Ceres, was discovered in 1801 by the astronomer Piazzi. Interestingly, this event took place on the first day of the new century. Other large asteroids – Pallas, Juno, Vesta were discovered a few years later. Astronomers decided that it was useless to look for asteroids and stopped research work.
The German astronomer Henke resumed his search. in 1848. 38 years after the discovery of the last asteroid at that time, a new small object was discovered, called Asteya. Inspired by success, astronomers stepped up their search and discovered at least one new asteroid every year (except 1945).
In the late 20th century, a new method of astrophotography was used to search for new asteroids. This photograph used an ultra-long exposure, and the asteroids left light lines in the picture. Using this method, it became possible to search for new asteroids much faster. For example, Max Wolf alone, without the involvement of a team of astronomers, managed to detect almost two and a half hundred asteroids.
Exploring asteroids today
The study of asteroids makes a huge contribution to science. Thanks to this, astronomers are enriched with knowledge about the solar system and its origin, better understand the universe and its structures. Huge efforts of scientists are spent on studying the composition of asteroids.
The study of asteroids provides an opportunity to refine and enrich knowledge about the Earth and its formation. It is known that the current conditions on our planet can be maintained solely by the presence of a large amount of water in liquid form. At the initial stages of development, the Earth was heated so much that it is unlikely that after it cooled down, huge reserves of water could form on it. It was previously assumed that comets brought water to Earth, but further studies have shown that its composition differs from that of the earth.
Only at the beginning of the 21st century, ice deposits were discovered on one of the asteroids – Themis. This discovery suggested that water was brought to Earth by asteroids.
So the study of these small objects helps to generalize, systematize knowledge about the Earth, the solar system and clarify existing data. Asteroids can be a source of raw materials – iron, cobalt, nickel, and hydrogen.
Astronomers study asteroids in the solar system in order to notice and prevent danger in time. After all, some of these cosmic bodies pose a potential threat to our planet. A collision of an asteroid with the Earth can have catastrophic and irreversible consequences. Numerous disaster films tell about what can happen to our planet in a collision with an asteroid.
One of the asteroids potentially dangerous for our planet in the solar system is Apophis with a diameter of 325 m. In 2029, it will pass very close to the Earth. The possibility of a collision with the planet in 2036 is not ruled out. Although recent studies of the trajectory of this object allow us to assume that it does not pose a danger to the Earth. A detailed study of such objects allows you to notice the danger emanating from space in time.
Mathematical modeling shows that a collision of the Earth with an asteroid with a diameter of 3 km is enough for a space planetary catastrophe. The largest crater on Earth, with a diameter of 300 km, was formed as a result of a collision of the Earth with a body not exceeding 10 km in diameter.
For the Earth, those objects that are potentially dangerous are those that are able to approach at a distance of less than 7.5 million km. The danger of an asteroid is estimated on a 10-point scale. 0 points means that the object does not pose a threat to the planet. 10 points means that the asteroid will inevitably collide with the Earth and provoke the death of mankind.
If our planet collides with an asteroid 10 km or more in diameter, then a huge shock wave is formed in the atmosphere. The space body will cause an earthquake and huge tsunamis. The heat wave is causing fires all over the world. They will throw soot into the atmosphere, soot, which will cover the Sun. A cold snap will begin, which all living organisms will not be able to survive.
Today, NASA completely excludes the possibility of a collision of the asteroid Apophis with the Earth. This conclusion was made after studying the data obtained after detailed observation of the object during its flyby in January 2013 at a distance of about 14 million km from the Earth.
It is now known that all main belt asteroids do not pose a danger to our planet. The previously potentially dangerous Apophis no longer poses a threat to us.
In 2004, the object 2004 FU162 was approaching near-Earth space at a distance of 6,530 km from the planet. Separate asteroids reached the earth’s atmosphere, but under the influence of gravity they were torn into small fragments and burned up in the air. In February 2013, an asteroid with a diameter of about 17 m and a weight of about 10 thousand tons entered the Earth’s atmosphere and exploded over Chelyabinsk at an altitude of about 20 km. As a result of combustion, a shock wave was formed that shattered glass in the city and nearby settlements.
Small space bodies have attracted the attention of mankind for several centuries. To date, several tens of thousands of asteroids are known to orbit the Sun in the main belt. The study of these objects is of great practical importance; it is one of the ways to solve the energy and raw materials problem. Since some space bodies pose a danger to the Earth, the study of their orbits can help prevent a catastrophe.
For a long time it was believed that the asteroid belt of the solar system was formed from a failed planet. The gravitational influence of early Jupiter prevented the formation of another solid planet, and between it and Mars, dust and gas particles formed a whole belt of small celestial bodies.
But recent studies by French and Brazilian astronomers cast doubt on this hypothesis of their origin. They compared the chemical composition and structure of various objects of the main belt and noticed that some of them are close in their properties to solid planets, and some to gas giants. A new hypothesis was put forward for the origin of asteroids. Presumably, they arose at the dawn of the formation of the solar system from fragments of substances left after the formation of the planets.
Composition and physical parameters
What are asteroids made of? To find out their chemical composition, astrophysicists examined the color of objects, as well as the spectrum of light reflected from their surface. It turned out that there are three main spectral classes that reflect the composition of asteroids:
- C (carbon) – the most common group, more than 75% of the total.
- S (silicate) – the surface of the bodies contains a greater amount of silicon compounds. They account for 17% of all known objects of this type.
- M (metal) – the surface consists of iron, nickel, aluminum, titanium and other common metals.
As the asteroid belt and Kuiper belt are explored, new rarer spectral types of these small solar system bodies are being discovered. At the moment, there are 12 of them. But such a classification is not entirely accurate, because. bodies belonging to the same class do not always have the same surface composition.
The size of an asteroid is calculated in various ways. In the case of large objects, it is convenient to use the transit method. Such bodies during their movement pass against the background of stars, which is recorded by observers from the Earth. Knowing the duration of the coverage of the star and the remoteness of the object, it is quite easy and accurate to determine its size.
Also, the size can be determined by the brightness of sunlight reflected from their surface. This method is called polarimetry, and it also allows you to determine the shape of a small celestial body. In order for a space object to be called an asteroid, its size must exceed 30 m. Most of the known ones do not exceed a hundred meters in diameter, and only one registered asteroid has a diameter of 900 km. This is Ceres and at the moment it has been transferred to the group of dwarf planets.
The mass of all asteroids is relatively small by the standards of the solar system. This value, according to various estimates, ranges from 3 * 1021 to 3 * 1026 kg (no more than 0.05% of the mass of the Earth). Moreover, more than half of this value is concentrated in the 4 largest: Vesta, Pallas, Juno and Hygea.
Families and their movement
At the beginning of the 20th century, the Japanese astronomer Hirayama made an amazing discovery. He observed the movement of the main belt asteroids for a long time and came to the conclusion that most of them can be divided into groups with similar orbital path parameters. This phenomenon of grouping of asteroids is explained by the fact that earlier a large celestial body was split into several fragments, which continued their movement near the “donor”. Such groups are called families.
The family is named after its largest member. The largest families of the main belt are:
- the Flora family – more than 7.5 thousand objects;
- the Vesta family – about 6 thousand;
- family of Eunomia – 4.7 thousand;
- Eos family – 4.4 thousand.
Read also Europa satellite At the moment, three dozen such groups of asteroids are officially recognized. Their boundaries are quite vague, but most are within the main belt. Every third object in this area is included in a separate group.
The asteroids of the Solar System that are in families and travel separately have similar motion characteristics. They revolve around the central star of our system in the same direction as most planets. The orbital paths of objects in the main belt have a slight eccentricity and a moderate inclination. Almost all of them do not go beyond the belt. One of the rare exceptions is Pallas.
The average speed of most asteroids in the solar system is about 20 km/s. Their complete revolution around the Sun ranges from 3 to 9 years.
Planets with their gravity affect the movement of asteroids in the solar system. Planetary perturbations deviate the orbits of small bodies in different directions, but Jupiter attracts the most. The most variable parameters of the orbital path are the eccentricity and the angle of inclination. Constantly mixing within the belt, asteroids collide with each other and form more and more new celestial bodies.
Interaction with the Earth
It is estimated that for the complete destruction of human civilization and global changes in the atmosphere and climate, the Earth needs to collide with an asteroid with a diameter of only 3 km. The largest impact crater on the planet is the South African crater Vredefort, whose diameter is 300 km. It was formed 2 billion years ago when the Earth collided with a small celestial body not exceeding 10 km.
Potentially dangerous for our planet are those objects of the main asteroid belt that can approach it at a distance of less than 7.5 million km. The danger of an asteroid is estimated on the Turin scale from 0 to 10. A zero mark means an extremely low probability of a collision and no damage when it enters the planet’s atmosphere. Asteroids with 10 points will inevitably collide with the Earth and cause a global catastrophe leading to the death of mankind.
As of June 2018, all main belt asteroids have a score of no higher than 0 on the Turin scale. Previously, Apophis (4 points) and (144898) 2004 VD17 (2 points) were considered to be some threat, but their indicators also dropped to zero.
Reducing the height of the Karman lineIn the 21st century, the closest to the Earth approached:
- 2008 TS26 – flew over the planet at a distance of 6 thousand km October 9, 2008;
- 2004 FU162 – approached 6530 km on March 31, 2004;
- 2009 VA – 14 thousand km November 6, 2009.
Some asteroids of the solar system reached the Earth’s atmosphere, but they were so small that they broke apart before reaching the surface of the planet, leaving only small fragments.
In February 2013, an asteroid measuring about 17 m and weighing up to 10 * 106 kg entered the atmosphere of our planet. It exploded at an altitude of 20 km above Chelyabinsk and its environs. According to various researchers, the explosion power ranged from 100 kilotons to 1.5 megatons of TNT. The combustion of the object in the earth’s atmosphere was accompanied by a strong shock wave, which knocked out a large number of glasses in nearby settlements. Also, the collision of an asteroid with the Earth provoked an earthquake with a magnitude of 4 points in the southwestern regions of Chelyabinsk.
The fall of the asteroid Chelyabinsk was the largest incident of its kind after the collision of the Earth with the Tunguska meteorite. It happened in 1908 in the area of the right tributary of the Yenisei River. The power of the explosion was about 40 megatons, which provoked a massive shaft of trees in the taiga on an area of more than 2 thousand square meters. km.
NASA funds most of the ongoing programs related to space security and the protection of the Earth from asteroids in the solar system. The largest projects “LINEAR” and “Pan-STARRS”, using the most powerful telescopes, track up to ten thousand small bodies annually. Also, the detection of potentially dangerous space objects is carried out from near-Earth orbit thanks to small satellites, such as the Canadian “NEOSSat”. NASA and other space agencies spend hundreds of millions of dollars to finance these projects.
Asteroids in the Earth’s Past
What happens if an asteroid larger than 10 km in diameter collides with the Earth? The first catastrophic event will be a giant shock wave in the atmosphere. Then the body will fall to the surface of the planet, which will end either with an unprecedented earthquake or a tsunami several hundred meters high. The heat wave will cause forest fires around the globe, which will trigger the release of huge amounts of soot and soot into the atmosphere. A sharp cooling will begin due to the fact that the polluted atmosphere will not be able to pass the sun’s rays in sufficient quantities. The climate on the planet will change irreversibly, and many living organisms will die out.
One of these collisions occurred 65 million years ago. On the Yucatan Peninsula in the Gulf of Mexico, evidence of this catastrophe has been preserved – the Chicxulub impact crater with a diameter of 180 km. A large space object about 10 km in size led to the complete extinction of dinosaurs on our planet. Some researchers also explain the Permian mass extinction of living organisms, which happened 250 million years ago, by the fall of a large asteroid.
Assumptions about how asteroids turned out
There are 2 hypotheses for the appearance of these objects:
The first hypothesis is that these fragments appeared due to the explosion of the planet Phaeton. Although this is considered a myth. It seems that highly developed beings lived on the planet. But a nuclear catastrophe destroyed the planet. But when studying meteorites, it turned out that the material of a single planet would clearly not be enough to obtain such different asteroids. And the impressive age of meteorites shows that asteroids were crushed for quite a long time.
The second hypothesis is the collision of protoplanetary bodies. The planets were formed from a cloud of gas and dust. But together between Jupiter and Mars, protoplanetary bodies formed, which then collided and asteroids were obtained.
How do we know about the composition of asteroids?
With varying degrees of accuracy, the chemistry and mineralogy of asteroids can be judged on the basis of various direct and indirect research methods:
- The position of its orbit in the solar system will help to estimate the composition of the object. As a rule, the farther from the Sun a small cosmic body, the more volatile substances in its composition, in particular, water ice.
- An important role in solving the problem is played by the spectral characteristics of the asteroid. However, the analysis of the reflected spectrum still does not allow one to judge unambiguously which substances predominate in the composition of a given body.
- The study of meteorites – fragments of asteroids falling on the Earth’s surface, makes it possible to accurately determine their mineral and chemical composition. Unfortunately, the origin of the meteorite is not always known.
- Finally, the most complete data on what an asteroid is made of can be obtained by analyzing its rocks using an interplanetary automatic apparatus. To date, several objects have been studied by this method.
Near earth objects
Near-Earth or near-Earth asteroids are called asteroids whose orbital perihelion does not exceed 1.3 astronomical units. Special space missions were sent to study some of them.
- Eros is a relatively large body with dimensions of approximately 34 × 11 × 11 km and a mass of 6.7 × 1012 tons, belonging to class S. This stony asteroid was studied in 2000 by the NEAR Shoemaker spacecraft. In addition to silicate rocks, it contains about 3% of metals. These are mainly iron, magnesium, aluminum, but there are also rare metals: zinc, silver, gold and platinum.
- Itokawa is also an S class asteroid. It is small – 535 × 294 × 209 m – and has a mass of 3.5 × 107 tons. Dust from the surface of Itokawa was brought to Earth by the return capsule of the Japanese Hayabusa probe in 2010. Dust particles contain minerals of the olivine, pyroxene, and plagioclase groups. The Itokawa soil is characterized by a high percentage of iron in silicates and a low content of this metal in free form. It has been established that the asteroid substance was subjected to thermal and impact metamorphism.
- Ryugu, a class C asteroid, is currently being studied by the Hayabusa-2 spacecraft. It is believed that the composition of such bodies has not changed much since the formation of the solar system, so the study of Ryugu is of great interest. The delivery of samples, which will allow us to study in more detail what the asteroid consists of, is planned for the end of 2020.
- Bennu is another object near which a space mission is currently operating – the OSIRIS-Rex station. This special class B carbon asteroid is also regarded as a source of important knowledge about the history of the solar system. The Bennu soil is supposed to be delivered to Earth for detailed study in 2023.
About the development prospects
Asteroids have long attracted attention as a potential source of rare and precious metals: osmium, palladium, iridium, platinum, gold, as well as molybdenum, titanium, cobalt and others. The arguments in favor of mining them on asteroids are based on the fact that the earth’s crust is poor in heavy elements due to gravitational differentiation. It is assumed that, as a result of the same process, the M asteroids are rich, in addition to iron and nickel, in these metals. In addition, the distribution of elements in the composition of C-asteroids that have not undergone differentiation is quite uniform.
Using these considerations, companies declaring their desire to develop asteroids periodically stir up interest in the topic. For example, in July 2015, the media bypassed the message about the close flyby of the platinum asteroid 2011 UW158. The estimate of its reserves reached more than five trillion dollars, but it turned out to be clearly exaggerated.
Nevertheless, there are still valuable raw materials on asteroids. The question of the expediency of its development rests on such problems as a reliable estimate of reserves, the cost of flights and production, and, of course, the required technological level. In the short term, these tasks can hardly be solved, so humanity is still very far from the development of asteroids.
Some people think that the asteroid belt is a very dense collection of celestial bodies, but this is not so. As of 2020, more than 300 thousand asteroids are known to form this belt, and their total number may exceed several million. However, due to the large length of the belt, they are located at a great distance from each other. Not a single spacecraft passing through this belt has ever collided with any object. Moreover, the probability of such a collision, or even an accidental approach of a probe to an asteroid, is less than one in a billion.
The total mass of all celestial bodies in the main belt is estimated at 3.4 x 1021 kg, which is 1600 times less than the mass of the Earth. At the same time, a third of this mass falls on one object – Ceres. This is a dwarf planet, previously considered the largest asteroid.
It has been observed that asteroids that are closer to the star have a greater reflectivity. Also, there is less water in the composition of these celestial bodies. It is likely that solar radiation literally “blew” water and other light elements into remote areas of the main belt.
The temperature near the surface of asteroids also depends on the distance to the Sun. At a distance of 2.2 AU from the star the temperature is – 73 ° C, and at a distance of 3.2 a. e. it drops to – 108 ° C.
Automatic interplanetary station Dawn near the asteroid Vesta and the dwarf planet Ceres (computer graphics). Image: Wikimedia Commons With the advent of the space age, it became possible to study asteroids using spacecraft. First, the asteroids were photographed by the Galileo probe, which photographed the asteroids Ida and Gaspra in 1993. Since then, every apparatus flying into deep space necessarily flies past some object in the main belt along the way and photographs it.
The first space probe built specifically to explore an asteroid is the NEAR Shoemaker. It was launched in 1996, and in February 2000 it entered the orbit of the asteroid Eros. It was possible to study in detail its chemical composition, as well as build a three-dimensional model of a celestial body. In 2001, the probe landed on Eros and for two weeks explored its soil at a depth of up to 10 cm.
In 2003, the Japanese Hayabusa probe was launched, which explored the Itokawa asteroid. The device was able to collect soil samples from Itokawa and send them to Earth.
The next vehicle to explore the main belt is the DAWN station. In 2011-2012, she studied the asteroid Vesta, and from 2015 to 2018, Ceres. As a result, almost 69 thousand photographs of these objects and many other data were obtained.
Weight and dimensions: from dwarfs to giants
The sizes of asteroids vary greatly – from a few tens of meters across to hundreds of kilometers. The largest asteroid is Ceres, its dimensions are 975 × 909 km. The largest also include Pallas, Juno, Psyche, Vesta. The diameter of these asteroids exceeds 100 km.
These celestial bodies have an irregular shape, since most of them are fragments of their predecessors. The exception is the largest asteroids, which more or less resemble spheres. Some of these space objects have satellites. According to the latest data, there are even double and triple asteroids.
The masses of asteroids also vary and strongly depend on the size of the celestial body. For example, at Ceres it is 9.5⋅1020 kg. In general, more than half (51%) of the mass of the entire main asteroid belt in the solar system is concentrated in the four largest asteroids.
All asteroids rotate, and, as a rule, in a rather chaotic way. The duration of the day on these celestial bodies is mainly from 6 to 12 hours. Scientists believe that the direction and speed of their rotation are due to the numerous collisions of the asteroid with its nearest neighbors. The exception is the most massive Ceres, Pallas and Vesta, which have direct rotation.
The speed of an asteroid can reach 40 km per second, although this characteristic depends on many factors and sometimes differs greatly.
Orbits and asteroid belts
Most of these objects are within a rather narrow ring located between the orbits of Mars and Jupiter, at a distance of 2.2 AU from the Sun. e. This cluster is called the main asteroid belt. But there are other “popular places” in our system: the Kuiper belt beyond the orbit of Neptune, as well as the scattered disk and the Oort cloud. All of them are located on the very edge of our star system, at a great distance from the Sun.
The distribution of objects in the main asteroid belt is not uniform. It has significant voids, called gaps or Kirkwood hatches, and dense clusters of objects, called families. The reason for this heterogeneity is the influence of the powerful gravity of the planets on the orbits of asteroids.
The families consist of asteroids with approximately the same orbital characteristics, which suggests that they are fragments of a larger belt object that once broke apart for one reason or another.
In the 19th century, astronomers believed that all asteroids were within the main belt. But it soon became clear that this was not entirely true. In 1906, an object was discovered orbiting Jupiter, overtaking it by 55.5 degrees. They named him Achilles. After some time, it turned out that this was only the first asteroid from a very large group, which received the code name “Greeks”.
Another cluster of asteroids was discovered, also following Jupiter’s orbit, but 60 degrees behind the gas giant. They were called “Trojans”. The orbits of both groups are quite stable, since they are located at the Lagrange points. The names of the asteroids were borrowed from Homer’s Iliad, so now literally all the heroes of the Trojan War can be found in the orbit of Jupiter.
There is another large group – the so-called near-Earth asteroids, whose orbits can dangerously approach our planet. Therefore, special attention is directed to them. The first objects from this group were discovered in 1932, they were named Apollo and Amur. Their orbits are very diverse: some of them from time to time return to the asteroid belt, others fly even farther than it, and others, on the contrary, “huddle” closer to the Sun.
This group is the most dangerous asteroids, the probability of collision with which is the highest. They are difficult to track, small asteroids are difficult to detect even with a radar or telescope. Now about 2 thousand objects larger than 1 km are known, which periodically cross the Earth’s orbit.
The so-called centaurs, an amazing hybrid of an asteroid and a comet, should be attributed to a separate group of celestial bodies. One of these objects is Chiron, which from time to time spreads a beautiful cometary tail. Although, in size it is much larger than any comet.
Where do asteroids and comets come from?
Both asteroids and comets are debris left over from the matter that formed the solar system almost 5 billion years ago. Stone and metal asteroids formed closer to the Sun. And ice comets formed further.
Because of their luxurious and highly visible tails, comets have been known since ancient times. The word comet comes from the ancient Greek for “long hair”.
Asteroids are much more difficult to detect. Therefore, nothing was known about their existence until the 19th century. Only then did telescopes become powerful enough to detect them. In a telescope, the asteroid looks like a faint star, just a point of light. And so their name comes from the word “star”.
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