Composite image (to scale) of asteroids taken in high resolution. For 2011, these were, from largest to smallest: (4) Vesta, (21) Lutetia, (253) Matilda, (243) Ida and its satellite Dactyl, (433) Eros, (951) Gaspra, (2867) Steins, (25143) Itokawa

Asteroid (common until 2006 synonym - minor planet) is a relatively small celestial body that orbits around . Asteroids are significantly inferior in mass and size, have an irregular shape and do not have, although they may also have.

Definitions

Comparative sizes of the asteroid (4) Vesta, the dwarf planet Ceres and the Moon. Resolution 20 km per pixel

The term asteroid (from other Greek ἀστεροειδής - “like a star”, from ἀστήρ - “star” and εἶδος - “appearance, appearance, quality”) was coined by the composer Charles Burney and introduced by William Herschel on the basis that these objects are When viewed through a telescope, they looked like dots, unlike the planets, which look like disks when viewed through a telescope. The exact definition of the term "asteroid" is still not established. Until 2006, asteroids were also called minor planets.

The main parameter by which classification is carried out is body size. Bodies with a diameter of more than 30 m are considered asteroids, smaller bodies are called.

In 2006, the International Astronomical Union classified most asteroids as.

Asteroids in the solar system

Main asteroid belt (white) and Jupiter's Trojan asteroids (green)

At the moment, hundreds of thousands of asteroids have been discovered in the solar system. As of January 11, 2015, there were 670,474 objects in the database, of which 422,636 had precise orbits and an official number, more than 19,000 of which had officially approved names. It is assumed that in the solar system there may be from 1.1 to 1.9 million objects larger than 1 km. Most of the currently known asteroids are concentrated within , located between the orbits and .

The largest asteroid in the solar system was considered to be approximately 975 × 909 km in size, but since August 24, 2006, it has received the status. The other two largest asteroids are (2) Pallas and have a diameter of ~500 km. (4) Vesta is the only asteroid belt object that can be observed with the naked eye. Asteroids moving in other orbits can also be observed during the period of passage near (for example, (99942) Apophis).

The total mass of all asteroids of the main belt is estimated at 3.0-3.6·10 21 kg, which is only about 4% of the mass. The mass of Ceres is 9.5 10 20 kg, that is, about 32% of the total, and together with the three largest asteroids (4) Vesta (9%), (2) Pallas (7%), (10) Hygiea (3% ) - 51%, that is, the vast majority of asteroids have an insignificant mass by astronomical standards.

Exploring asteroids

The study of asteroids began after the discovery of the planet 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 organized a group of 24 astronomers. Since 1789, this group has been looking for a planet, which, according to the Titius-Bode rule, should have been 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 the stars in the area of ​​the zodiac constellations at a certain moment. In subsequent nights, the coordinates were checked, and objects that moved a greater distance were highlighted. The estimated displacement of the planet being sought must have been about 30 arc seconds per hour, which should have been easily noticed.

Ironically, the first asteroid, 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 searching, most astronomers decided that there was nothing more there and stopped researching.

However, Karl Ludwig Henke persisted, and in 1830 he resumed the search for new asteroids. Fifteen years later, he discovered Astrea, the first new asteroid in 38 years. He also discovered Hebe less than two years later. After that, other astronomers joined the search, and then at least one new asteroid was discovered per year (with the exception of 1945).

In 1891, Max Wolff was the first to use the astrophotography method to search for asteroids, in which asteroids left short light lines in photographs with a long exposure period. This method significantly accelerated the discovery of new asteroids compared to previously used methods of visual observation: Max Wolf single-handedly discovered 248 asteroids, starting with (323) Brucius, while a little more than 300 were discovered before him. Now, a century later, 385 thousand asteroids have official number, and 18 thousand of them are also a name.

In 2010, two independent teams of astronomers from the United States, Spain and Brazil announced that they had simultaneously discovered water ice on the surface of one of the largest main belt asteroids, Themis. This discovery allows us to understand the origin of water on Earth. At the beginning of its existence, the Earth was too hot to hold enough water. This substance was supposed to arrive later. It was assumed that comets could bring water to Earth, but the isotopic composition earth water and water in comets does not match. Therefore, it can be assumed that water was brought to the Earth during its collision with asteroids. The researchers also found complex hydrocarbons on Themis, including molecules that are the precursors of life.

Naming asteroids

At first, asteroids were given the names of the heroes of Roman and Greek mythology, later the discoverers got the right to call them whatever they like - for example, by their own name. At first, asteroids were given predominantly female names, only asteroids with unusual orbits received male names (for example, Icarus, approaching the Sun closer). Later, this rule was no longer observed.

Not every asteroid can get a name, but only one whose orbit is more or less reliably calculated. There have been cases when an asteroid was given a name decades after its discovery. Until the orbit is calculated, the asteroid is given a temporary designation reflecting the date of its discovery, such as 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 above example, this is the second half of February). The second letter indicates the serial number of the asteroid in the indicated crescent; in our example, the asteroid was discovered first. Since there are 24 crescents, and English letters- 26, 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 return to the beginning of the alphabet again, assigning index 2 to the second letter, at the next return - 3, etc.

After receiving the name, the official naming of the asteroid consists of a number (serial number) and a name - (1) Ceres, (8) Flora, etc.

Determining the shape and size of an asteroid

Asteroid (951) Gaspra. One of the first images of an asteroid taken from a spacecraft. Transmitted by the Galileo space probe during its flyby of Gaspra in 1991 (colors enhanced)

The first attempts to measure the diameters of asteroids, using the method of direct measurement of visible disks with a thread micrometer, were made by William Herschel in 1802 and Johann Schroeter in 1805. After them, in the 19th century, other astronomers measured the brightest asteroids in a similar way. The main disadvantage of this method was significant discrepancies in the results (for example, the minimum and maximum sizes of Ceres obtained by different scientists differed ten times).

Modern methods for determining the size of asteroids include methods of polarimetry, radar, speckle interferometry, transit and thermal radiometry.

One of the simplest and most qualitative is the transit method. During the movement of an asteroid relative to the Earth, it sometimes passes against the background of a distant star, this phenomenon is called the occultation of stars by an asteroid. By measuring the duration of the decrease in the brightness of a given star and knowing the distance to the asteroid, one can accurately determine its size. This method allows you to accurately determine the size of large asteroids, like Pallas.

The polarimetric method is to determine the size based on the brightness of the asteroid. The larger the asteroid, the more sunlight it reflects. However, the brightness of an asteroid strongly depends on the albedo of the asteroid's surface, which in turn is determined by the composition of its constituent rocks. For example, the asteroid Vesta, due to the high albedo of its surface, reflects 4 times more light than Ceres and is the most visible asteroid in the sky, which can sometimes be observed with the naked eye.

However, the albedo itself can also be determined quite easily. The fact is that the lower the brightness of the asteroid, that is, the less it reflects solar radiation in the visible range, the more it absorbs it and, heating up, then radiates it in the form of heat in the infrared range.

The polarimetry method can also be used to determine the shape of an asteroid, by registering changes in its brightness during rotation, and to determine the period of this rotation, as well as to identify large structures on the surface. In addition, the results obtained with infrared telescopes are used for size determination by thermal radiometry.

Classification of asteroids

The general classification of asteroids is based on the characteristics of their orbits and the description of the visible spectrum of sunlight reflected by their surface.

Orbit groups and families

Asteroids are combined into groups and families based on the characteristics of their orbits. Usually the group is named after the first asteroid that was discovered in a given orbit. Groups are relatively free formations, while families are denser, formed in the past during the destruction of large asteroids from collisions with other objects.

Spectral classes

In 1975, Clark R. Chapman, David Morrison, and Ben Zellner developed a classification system for asteroids based on color, albedo, and reflected sunlight spectrum characteristics. Initially, this classification defined only three types of asteroids:

Class C - carbon, 75% of known asteroids.
Class S - silicate, 17% of known asteroids.
Class M - metal, most of the rest.

This list was later expanded and the number of types continues to grow as more asteroids are studied in detail:

Class A - characterized by a fairly high albedo (between 0.17 and 0.35) and a reddish color in the visible part of the spectrum.
Class B - in general, they belong to class C asteroids, but they almost do not absorb waves below 0.5 microns, and their spectrum is slightly bluish. The albedo is generally higher than that of other carbon asteroids.
Class D - characterized by a very low albedo (0.02-0.05) and an even reddish spectrum without clear absorption lines.
Class E - the surface of these asteroids contains such a mineral as enstatite and may resemble achondrites.
Class F - generally similar to class B asteroids, but without traces of "water".
Class G - characterized by low albedo and an almost flat (and colorless) reflection spectrum in the visible range, indicating strong ultraviolet absorption.
Class P - like class D asteroids, they are characterized by a rather low albedo, (0.02-0.07) and a smooth reddish spectrum without clear absorption lines.
Class Q - at a wavelength of 1 μm in the spectrum of these asteroids there are bright and broad lines of olivine and pyroxene, and, in addition, features indicating the presence of a metal.
Class R - characterized by a relatively high albedo and a reddish reflectance spectrum at a length of 0.7 µm.
Class T - is characterized by a low albedo and a reddish spectrum (with moderate absorption at a wavelength of 0.85 μm), which is similar to the spectrum of P- and D-class asteroids, but occupies an intermediate position in slope.
Class V - Asteroids of this class are moderately bright and quite close to the more common S class, which are also mainly composed of stone, silicates and iron (chondrites), but differ in S by a higher content of pyroxene.
Class J is a class of asteroids thought to have formed from the interior of Vesta. Their spectra are close to those of Class V asteroids, but they are distinguished by particularly strong absorption lines at a wavelength of 1 μm.

It should be borne in mind that the number of known asteroids assigned to any type does not necessarily correspond to reality. Some types are quite difficult to determine, and the type of a certain asteroid can be changed with more careful research.

Spectral classification problems

Initially, the spectral classification was based on three types of material that make up asteroids:

Class C - carbon (carbonates).
Class S - silicon (silicates).
Class M - metal.

However, there are doubts that such a classification unambiguously determines the composition of the asteroid. While the different spectral class of asteroids indicates their different composition, there is no evidence that asteroids of the same spectral type are made of the same materials. As a result, scientists did not accept the new system, and the introduction spectral classification stopped.

Size distribution

The number of asteroids noticeably decreases with their size. Although this generally follows a power law, there are peaks at 5 km and 100 km where there are more asteroids than would be expected from a logarithmic distribution.

Asteroid formation

In July 2015, the discovery of the 11th and 12th Neptune Trojans, 2014 QO441 and 2014 QP441, was reported by the Victor Blanco telescope's DECam camera. Thus, the number of Trojans at the L4 point of Neptune increased to 9. This survey also found 20 other objects that received the designation of the Minor Planet Center, including 2013 RF98, which has one of the longest orbital periods.

The objects of this group are given the names of the centaurs of ancient mythology.

The first discovered centaur was Chiron (1977). When approaching perihelion, it has a coma characteristic of comets, so Chiron is classified as both a comet (95P / Chiron) and an asteroid (2060 Chiron), although it is significantly larger than a typical comet.



Nathan Eismont,
Candidate of Physical and Mathematical Sciences, Leading Researcher(Space Research Institute RAS)
Anton Ledkov,
Researcher (Space Research Institute RAS)
"Science and Life" No. 1, 2015, No. 2, 2015

The solar system is usually perceived as an empty space in which eight planets circle, some with their satellites. Someone will remember several small planets, to which Pluto was recently attributed, about the asteroid belt, about meteorites that sometimes fall to the Earth, and about comets that occasionally decorate the sky. This idea is quite correct: not one of the many spacecraft has suffered from a collision with an asteroid or a comet - space is quite spacious.

And yet, to a large extent solar system contains not hundreds of thousands and not tens of millions, but quadrillions (ones with fifteen zeros) space bodies various sizes and weights. All of them move and interact according to the laws of physics and celestial mechanics. Some of them were formed in the earliest Universe and consist of its primordial matter, and this most interesting objects astrophysical research. But there are also very dangerous bodies - large asteroids, the collision of which with the Earth can destroy life on it. Tracking and eliminating the asteroid hazard is an equally important and exciting area of ​​work for astrophysicists.

History of the discovery of asteroids

The first asteroid was discovered in 1801 by Giuseppe Piasi, director of the observatory in Palermo (Sicily). He named it Ceres and at first believed minor planet. The term "asteroid", translated from ancient Greek - "like a star", was proposed by astronomer William Herschel (see "Science and Life" No. 7, 2012, article "The Tale of the Musician William Herschel, Who Doubled the Space"). Ceres and similar objects (Pallas, Juno and Vesta) discovered in the next six years were seen as points, not as disks in the case of the planets; at the same time, unlike the fixed stars, they moved like planets. It should be noted that the observations that led to the discovery of these asteroids were carried out purposefully in an attempt to find the "missing" planet. The fact is that already discovered planets were located in orbits spaced from the Sun at distances corresponding to Bode's law. In accordance with it, there should have been a planet between Mars and Jupiter. As you know, no planets were found in such an orbit, but an asteroid belt, called the main one, was later discovered approximately in this area. In addition, the Bode law, as it turned out, does not have any physical justification and is now considered simply as a kind of random combination of numbers. Moreover, discovered later (1848) Neptune was in an orbit that was not consistent with it.

After the discovery of the four mentioned asteroids, further observations for eight years did not lead to success. They were stopped due to the Napoleonic Wars, during which the town of Lilienthal near Bremen burned down, where meetings of astronomers - asteroid hunters were held. Observations resumed in 1830, but success came only in 1845 with the discovery of the asteroid Astrea. Since that time, asteroids have been discovered with a frequency of at least one per year. Most of them belong to the main asteroid belt, between Mars and Jupiter. By 1868, there were already about a hundred discovered asteroids, by 1981 - 10,000, and by 2000 - more than 100,000.

Chemical composition, shape, size and orbits of asteroids

If asteroids are classified according to their distance from the Sun, then the first group includes vulcanoids - a kind of hypothetical belt of small planets between the Sun and Mercury. Not a single object from this belt has yet been discovered, and although numerous impact craters formed by the fall of asteroids are observed on the surface of Mercury, this cannot serve as proof of the existence of this belt. Previously, the presence of asteroids there tried to explain the anomalies in the motion of Mercury, but then they were explained on the basis of relativistic effects. So the final answer to the question of the possible presence of Vulcanoids has not yet been received. This is followed by near-Earth asteroids belonging to four groups.

Main belt asteroids move in orbits located between the orbits of Mars and Jupiter, that is, at distances from 2.1 to 3.3 astronomical units (AU) from the Sun. The planes of their orbits are near the ecliptic, their inclination to the ecliptic lies mainly up to 20 degrees, reaching up to 35 degrees for some, eccentricities - from zero to 0.35. Obviously, the largest and brightest asteroids were the first to be discovered: the average diameters of Ceres, Pallas and Vesta are 952, 544 and 525 kilometers, respectively. How smaller size asteroids, the more of them: only 140 of the 100,000 main belt asteroids have an average diameter of more than 120 kilometers. The total mass of all its asteroids is relatively small, accounting for only about 4% of the mass of the Moon. Most big asteroid- Ceres - has a mass of 946 10 15 tons. The value itself seems very large, but it is only 1.3% of the mass of the Moon (735 10 17 tons). As a first approximation, the size of an asteroid can be determined by its brightness and by its distance from the Sun. But we must also take into account the reflective characteristics of the asteroid - its albedo. If the surface of the asteroid is dark, it glows weaker. It is for these reasons that in the list of ten asteroids, located in the figure in the order of their discovery, the third largest asteroid Hygiea is in last place.

Drawings illustrating the main asteroid belt tend to show many boulders moving fairly close together. In fact, the picture is very far from reality, since, generally speaking, a small total mass of the belt is distributed over its large volume, so that space is rather empty. All spacecraft launched to date beyond the orbit of Jupiter have passed through the asteroid belt without any appreciable risk of colliding with an asteroid. However, by the standards of astronomical time, collisions of asteroids with each other and with planets no longer look so unlikely, as can be judged by the number of craters on their surfaces.

Trojans- asteroids moving along the orbits of the planets, the first of which was discovered in 1906 by the German astronomer Max Wolf. The asteroid moves around the Sun in the orbit of Jupiter, ahead of it by an average of 60 degrees. Further, a whole group of celestial bodies was discovered moving ahead of Jupiter.

Initially, they received names in honor of the heroes of the legend of the Trojan War, who fought on the side of the Greeks besieging Troy. In addition to the asteroids leading Jupiter, there is a group of asteroids lagging behind it by about the same angle; they were named Trojans after the defenders of Troy. At present, asteroids of both groups are called Trojans, and they move in the vicinity of the Lagrange points L 4 and L 5 , points of stable motion in task of three tel. Celestial bodies that have fallen into their vicinity make oscillating motion without going too far. For reasons that have not yet been explained, there are about 40% more asteroids ahead of Jupiter than lagging behind. This was confirmed by recent measurements made by the American satellite NEOWISE using a 40-cm telescope equipped with detectors operating in the infrared range. Measurements in the infrared range significantly expand the possibilities of studying asteroids in comparison with those that give visible light. Their effectiveness can be judged by the number of asteroids and comets in the solar system cataloged using NEOWISE. There are more than 158,000 of them, and the mission of the apparatus continues. Interestingly, the Trojans are markedly different from most of the main belt asteroids. They have a matte surface, a reddish-brown color, and belong mainly to the so-called D-class. These are asteroids with a very low albedo, that is, with a weakly reflective surface. Similar to them can be found only in the outer regions of the main belt.

It's not just Jupiter that has Trojans; other planets of the solar system, including the Earth (but not Venus and Mercury), also accompany the Trojans, grouping in the vicinity of their Lagrange points L 4 , L 5 . The Earth Trojan asteroid 2010 TK7 was discovered with the help of the NEOWISE telescope quite recently - in 2010. It moves ahead of the Earth, while the amplitude of its oscillations near the point L 4 is very large: the asteroid reaches a point opposite to the Earth in motion around the Sun, and unusually far out of the plane of the ecliptic.

Such a large amplitude of oscillations leads to its possible approach to the Earth up to 20 million kilometers. However, a collision with the Earth, at least in the next 20,000 years, is completely excluded. The motion of the terrestrial Trojan is very different from the motion of the Jupiter Trojans, which do not leave their Lagrange points for such significant angular distances. This nature of the motion makes it difficult for spacecraft to reach it, because, due to the significant inclination of the Trojan’s orbit to the ecliptic plane, reaching the asteroid from the Earth and landing on it requires too high a characteristic velocity and, consequently, high fuel consumption.

Kuiper Belt lies outside the orbit of Neptune and extends up to 120 AU. from the sun. It is close to the plane of the ecliptic, inhabited by a huge number of objects that include water ice and frozen gases, and serves as a source of so-called short-period comets. The first object from this region was discovered in 1992, and to date, more than 1300 have already been discovered. Since the celestial bodies of the Kuiper belt are located very far from the Sun, it is difficult to determine their size. This is done on the basis of measurements of the brightness of the light they reflect, and the accuracy of the calculation depends on how well we know the value of their albedo. Measurements in the infrared range are much more reliable, since they give the levels of self-radiation of objects. Such data were obtained by the Spitzer space telescope for the most large facilities Kuiper belts.

One of the most interesting objects of the belt is Haumea, named after the Hawaiian goddess of fertility and childbearing; it is part of a family formed as a result of collisions. This object appears to have collided with another one half the size. The impact caused large ice chunks to scatter and caused Haumea to rotate with a period of about four hours. Such a fast spin gave it the shape of an American football or melon. Haumea is accompanied by two satellites - Hi'iaka (Hi'iaka) and Namaka (Namaka).

According to currently accepted theories, about 90% of Kuiper belt objects move in distant circular orbits beyond the orbit of Neptune - where they formed. Several dozen objects of this belt (they are called centaurs, because, depending on the distance to the Sun, they manifest themselves either as asteroids or as comets), possibly formed in regions closer to the Sun, and then the gravitational influence of Uranus and Neptune transferred them to high elliptical orbits with aphelions up to 200 AU and great inclinations. They formed a disk 10 AU thick, but the actual outer edge of the Kuiper belt has not yet been determined. More recently, Pluto and Charon were considered as the only examples the largest objects of ice worlds in the outer part of the solar system. But in 2005, another planetary body was discovered - Eris (named after the Greek goddess of discord), whose diameter is slightly smaller than the diameter of Pluto (initially it was assumed that it was 10% larger). Eris moves in an orbit with a perihelion of 38 AU. and aphelion 98 a.u. She has no large satellite- Dysnomia. At first, Eris was planned to be considered the tenth (after Pluto) planet in the solar system, but then instead the International Astronomical Union excluded Pluto from the list of planets, forming a new class called dwarf planets, which included Pluto, Eris and Ceres. It is assumed that in the Kuiper belt there are hundreds of thousands of icy bodies with a diameter of 100 kilometers and at least a trillion comets. However, these objects are mostly relatively small—10–50 kilometers across—and not very bright. The period of their revolution around the Sun is hundreds of years, which greatly complicates their detection. If we agree with the assumption that only about 35,000 Kuiper belt objects have a diameter of more than 100 kilometers, then their total mass is several hundred times greater than the mass of bodies of this size from the main asteroid belt. In August 2006, it was reported that eclipses of the neutron star Scorpius X-1 were found in the X-ray data archive. small objects. This gave grounds to assert that the number of Kuiper belt objects with sizes of about 100 meters or more is approximately a quadrillion (10 15). Initially, in the earlier stages of the evolution of the solar system, the mass of Kuiper belt objects was much larger than now, from 10 to 50 Earth masses. At present, the total mass of all the bodies of the Kuiper belt, as well as the Oort cloud located even further from the Sun, is much less than the mass of the Moon. As computer simulations show, almost all of the mass of the primordial disk beyond 70 AU. was lost due to collisions caused by Neptune, which led to the grinding of belt objects into dust, which was swept into interstellar space by the solar wind. All of these bodies are of great interest, since it is assumed that they have been preserved in their original form since the formation of the solar system.

Oort cloud contains the most distant objects in the solar system. It is a spherical region that extends over distances from 5,000 to 100,000 AU. from the Sun and is considered as a source of long-period comets reaching up to inner region solar system. The cloud itself was not instrumentally observed until 2003. In March 2004, a team of astronomers announced the discovery of a planet-like object that orbits the Sun at a record distance, meaning it has a uniquely cold temperature.

This object (2003VB12), named Sedna after the Eskimo goddess who gives life to the inhabitants of the Arctic sea depths, approaches the Sun for a very short time, moving in a highly elongated elliptical orbit with a period of 10,500 years. But even during the approach to the Sun, Sedna does not reach the outer border of the Kuiper belt, which is located at 55 AU. from the Sun: its orbit lies between 76 (perihelion) and 1000 (aphelion) AU. This allowed the discoverers of Sedna to attribute it to the first observed celestial body from the Oort cloud, constantly located outside the Kuiper belt.

According to spectral characteristics, the simplest classification divides asteroids into three groups:
C - carbon (75% known),
S - silicon (17% known),
U - not included in the first two groups.

At present, the above classification is increasingly expanding and detailing, including new groups. By 2002, their number increased to 24. An example of a new group is the M-class of mostly metallic asteroids. However, it should be taken into account that the classification of asteroids according to the spectral characteristics of their surface is a very difficult task. Asteroids of the same class do not necessarily have identical chemical compositions.

Space missions to asteroids

Asteroids are too small for detailed study with ground-based telescopes. They can be imaged using radar, but for this they must fly close enough to the Earth. Enough interesting method determination of the size of asteroids - observation of occultations of stars by asteroids from several points along the path on a direct star - asteroid - a point on the Earth's surface. The method consists in the fact that according to the known trajectory of the asteroid, the points of intersection of the star-asteroid direction with the Earth are calculated, and along this path at some distances from it, determined by the estimated size of the asteroid, telescopes are installed that track the star. At some point, the asteroid obscures the star, it disappears for the observer, and then reappears. From the duration of the shading time and the known speed of the asteroid, its diameter is determined, and with a sufficient number of observers, the silhouette of the asteroid can also be obtained. There is now a community of amateur astronomers who are successfully making coordinated measurements.

Flights of spacecraft to asteroids open up incomparably more opportunities for their study. The asteroid (951 Gaspra) was first photographed by the Galileo spacecraft in 1991 on its way to Jupiter, then in 1993 it took the asteroid 243 Ida and its satellite Dactyl. But it was done, so to speak, incidentally.

The first spacecraft specifically designed for asteroid exploration was NEAR Shoemaker, which photographed the asteroid 253 Matilda and then went into orbit around 433 Eros with a landing on its surface in 2001. I must say that the landing was not originally planned, but after the successful study of this asteroid from the orbit of its satellite, they decided to try to make a soft landing. Although the device was not equipped with landing devices and its control system did not provide for such operations, the commands from the Earth managed to land the device, and its systems continued to function on the surface. In addition, the flyby of Matilda made it possible not only to obtain a series of images, but also to determine the mass of the asteroid from the perturbation of the trajectory of the apparatus.

As an incidental task (during the execution of the main one), the Deep Space apparatus explored the asteroid 9969 Braille in 1999 and the Stardust apparatus, the asteroid 5535 Annafranc.

With the help of the Japanese Hayabus apparatus (translated as “hawk”) in June 2010, it was possible to return soil samples to Earth from the surface of asteroid 25 143 Itokawa, which belongs to near-Earth asteroids (Apollos) of spectral class S (silicon). The photo of the asteroid shows rugged terrain with many boulders and cobblestones, of which more than 1000 have a diameter of more than 5 meters, and some are up to 50 meters in size. We will return to this feature of Itokawa later.

The Rosetta spacecraft launched by the European space agency in 2004, to the comet Churyumov - Gerasimenko, on November 12, 2014, he safely landed the Philae module on its nucleus. Along the way, the spacecraft flew around asteroids 2867 Steins in 2008 and 21 Lutetia in 2010. The device got its name from the name of the stone (Rosetta), found in Egypt by Napoleonic soldiers near the ancient city of Rosetta on the Nile island of Philae, which gave the lander its name. Texts in two languages ​​are carved on the stone: ancient Egyptian and ancient Greek, which gave the key to revealing the secrets of the civilization of the ancient Egyptians - deciphering hieroglyphs. Choosing historical names, the project developers emphasized the purpose of the mission - to uncover the secrets of the origin and evolution of the solar system.

The mission is interesting because at the time of landing of the Philae module on the surface of the comet's nucleus, it was far from the Sun and therefore was inactive. As it approaches the Sun, the surface of the core heats up and the emission of gases and dust begins. The development of all these processes can be observed, being in the center of events.

Very interesting is the ongoing mission Dawn (Dawn), carried out under the NASA program. The device was launched in 2007, reached the asteroid Vesta in July 2011, then transferred to its satellite orbit and conducted research there until September 2012. Currently, the device is on its way to the largest asteroid - Ceres. On it is an electric rocket ion thruster. Its efficiency, determined by the speed of the expiration of the working fluid (xenon), is almost an order of magnitude higher than the efficiency of traditional chemical engines (see "Science and Life" No. 9, 1999, article "Space electric locomotive"). This made it possible to fly from the orbit of the satellite of one asteroid to the orbit of the satellite of another. Although the asteroids Vesta and Ceres move in fairly close orbits of the main asteroid belt and are the largest in it, they differ greatly in physical characteristics. If Vesta is a “dry” asteroid, then Ceres, according to ground-based observations, has water, seasonal water ice polar caps, and even a very thin layer of the atmosphere.

The Chinese also contributed to asteroid exploration by sending their Chang'e spacecraft to the asteroid 4179 Tautatis. He took a series of photographs of its surface, while the minimum flight distance was only 3.2 kilometers; truth, best shot was taken at a distance of 47 kilometers. The images show that the asteroid has an irregular elongated shape - 4.6 kilometers in length and 2.1 kilometers in diameter. The mass of the asteroid is 50 billion tons, its very curious feature is its very uneven density. One part of the asteroid's volume has a density of 1.95 g/cm 3 , the other one - 2.25 g/cm 3 . In this regard, it has been suggested that Tautatis was formed as a result of the union of two asteroids.

As for asteroid missions in the near future, one could start with the Japanese Aerospace Agency, which plans to continue its research program with the launch of the Hyabus-2 spacecraft in 2015, with the goal of returning soil samples from asteroid 1999 JU3 to Earth in 2020. The asteroid belongs to the spectral class C, is in an orbit that crosses the orbit of the Earth, its aphelion almost reaches the orbit of Mars.

A year later, that is, in 2016, the NASA OSIRIS-Rex project starts, the purpose of which is to return soil from the surface of the near-Earth asteroid 1999 RQ36, recently named Bennu and assigned to spectral class C. It is planned that the device will reach the asteroid in 2018 and in 2023 will deliver 59 grams of its rock to Earth.

Having listed all these projects, it is impossible not to mention an asteroid weighing about 13,000 tons, which fell near Chelyabinsk on February 15, 2013, as if confirming the statement of the famous American specialist on the asteroid problem Donald Yeomans: “If we do not fly to asteroids, then they fly to us ". This emphasized the importance of yet another aspect of the study of asteroids - the asteroid hazard and the solution of problems related to the possibility of asteroids colliding with the Earth.

Very unexpected way Asteroid research was initiated by the Asteroid Redirect Mission, or as it is known, the Keck Project. Its concept was developed by the Keck Institute for Space Research in Pasadena (California). William Myron Keck is a well-known American philanthropist who founded the US Scientific Research Foundation in 1954. In the project, it was assumed as an initial condition that the task of exploring the asteroid is solved with the participation of a person, in other words, the mission to the asteroid must be manned. But in this case, the duration of the entire flight with the return to Earth will inevitably be at least several months. And what is most unpleasant for a manned expedition, in the event of an emergency, this time cannot be reduced to acceptable limits. Therefore, it was proposed, instead of flying to the asteroid, to do the opposite: to deliver, using unmanned vehicles, the asteroid to the Earth. But not to the surface, as it happened with the Chelyabinsk asteroid, but to an orbit similar to the lunar one, and send a manned spacecraft to the asteroid that has become close. This ship will approach it, capture it, and the astronauts will study it, take rock samples and deliver them to Earth. And in an emergency, astronauts will be able to return to Earth within a week. As the main candidate for the role of an asteroid moved in this way, NASA has already chosen the near-Earth asteroid 2011 MD, which belongs to the cupids. Its diameter is from 7 to 15 meters, density is 1 g/cm 3 , that is, it can look like a loose pile of rubble weighing about 500 tons. Its orbit is very close to the orbit of the Earth, inclined to the ecliptic by 2.5 degrees, and the period is 396.5 days, which corresponds to a semi-major axis of 1.056 AU. It is interesting to note that the asteroid was discovered on June 22, 2011, and on June 27 it flew very close to the Earth - only 12,000 kilometers.

A mission to capture an asteroid into Earth satellite orbit is planned for the early 2020s. The spacecraft, designed to capture the asteroid and transfer it to a new orbit, will be equipped with xenon electric thrusters. The operations to change the asteroid's orbit also include a gravitational maneuver near the Moon. The essence of this maneuver is to control the movement with the help of electric rocket engines, which will ensure the passage of the vicinity of the Moon. At the same time, due to the influence of its gravitational field, the speed of the asteroid changes from the initial hyperbolic (that is, leading to the departure from the Earth's gravitational field) to the speed of the Earth's satellite.

Formation and evolution of asteroids

As already mentioned in the section on the history of the discovery of asteroids, the first of them were discovered during the search for a hypothetical planet, which, in accordance with the Bode law (now recognized as erroneous), should have been in orbit between Mars and Jupiter. It turned out that there is an asteroid belt near the orbit of the never discovered planet. This served as the basis for constructing a hypothesis, according to which this belt was formed as a result of its destruction.

The planet was named Phaeton after the son of the ancient Greek sun god Helios. Calculations simulating the process of Phaeton's destruction did not confirm this hypothesis in all its varieties, starting from the planet being torn apart by the gravity of Jupiter and Mars and ending with a collision with another celestial body.

The formation and evolution of asteroids can only be considered as a component of the processes of the emergence of the solar system as a whole. At present, the generally accepted theory suggests that the solar system arose from a primordial accumulation of gas and dust. A disk was formed from the cluster, the inhomogeneities of which led to the emergence of planets and small bodies of the solar system. This hypothesis is supported by modern astronomical observations, which make it possible to detect the development of planetary systems of young stars in their early stages. Computer modelling also confirms it by constructing pictures that are surprisingly similar to pictures of planetary systems at certain phases of their development.

At the initial stage of the formation of the planets, the so-called planetesimals arose - the "embryos" of the planets, on which dust then adhered due to the gravitational influence. As an example of such an initial phase of planetary formation, the asteroid Lutetia is pointed out. This rather large asteroid, reaching 130 kilometers in diameter, consists of a solid part and a thick (up to a kilometer) layer of dust adhering, as well as boulders scattered over the surface. As the mass of the protoplanets increased, the force of attraction and, as a result, the force of compression of the forming celestial body increased. There was a heating of the substance and its melting, leading to the stratification of the protoplanet according to the density of its materials, and the transition of the body to a spherical shape. Most researchers are inclined to the hypothesis that during the initial phases of the evolution of the solar system, many more protoplanets were formed than the planets and small celestial bodies observed today. At that time, the formed gas giants - Jupiter and Saturn - migrated into the system, closer to the Sun. This introduced significant disorder into the movement of the emerging bodies of the solar system and caused the development of a process called the period of heavy bombardment. As a result of resonant influences from mainly Jupiter, part of the resulting celestial bodies was ejected to the outskirts of the system, and part was thrown onto the Sun. This process went on from 4.1 to 3.8 billion years ago. traces of the period they call late stage heavy bombardment, remained in the form of many impact craters on the Moon and Mercury. The same thing happened with the formation of bodies between Mars and Jupiter: the frequency of collisions between them was high enough to prevent them from turning into objects larger and more correct form than we see today. It is assumed that among them there are fragments of bodies that went through certain phases of evolution, and then split during collisions, as well as objects that did not have time to become parts of more large bodies and thus represent examples of older formations. As mentioned above, the Lutetia asteroid is just such a sample. This was confirmed by the studies of the asteroid carried out by the Rosetta spacecraft, including shooting during a close flyby in July 2010.

Thus, Jupiter plays a significant role in the evolution of the main asteroid belt. Due to its gravitational influence, we have obtained the currently observed picture of the distribution of asteroids within the main belt. As for the Kuiper belt, the influence of Neptune is added to the role of Jupiter, leading to the ejection of celestial objects into this remote region of the solar system. It is assumed that the influence of the giant planets extends to an even more distant Oort cloud, which, however, formed closer to the Sun than it is now. In the early phases of the evolution of approaching the giant planets, the primordial objects (planetesimals) in their natural motion performed what we call gravitational maneuvers, replenishing the space attributed to the Oort cloud. Being at such great distances from the Sun, they are also affected by the stars of our Galaxy - Milky Way, which leads to their chaotic transition to return trajectories to a close region of circumsolar space. We observe these planetesimals as long period comets. As an example, one can point to the brightest comet of the 20th century - Comet Hale-Bopp, discovered on July 23, 1995 and reached perihelion in 1997. The period of its revolution around the Sun is 2534 years, and the aphelion is at a distance of 185 AU. from the sun.

Asteroid-comet hazard

Numerous craters on the surface of the Moon, Mercury and other bodies of the solar system are often mentioned as an illustration of the level of asteroid-comet hazard for the Earth. But such a reference is not entirely correct, since the vast majority of these craters were formed during the "period of heavy bombardment." Nevertheless, on the surface of the Earth, using modern technologies, including the analysis of satellite imagery, it is possible to detect traces of collisions with asteroids, which belong to much later periods of the evolution of the solar system. The largest and oldest known crater, Vredefort, is located in South Africa. Its diameter is about 250 kilometers, its age is estimated at two billion years.

The Chicxulub crater on the coast of the Yucatan Peninsula in Mexico was formed after an asteroid impact 65 million years ago, equivalent to the energy of an explosion of 100 teraton (10 12 tons) of TNT. It is now believed that the extinction of the dinosaurs was a consequence of this catastrophic event, which caused tsunamis, earthquakes, volcanic eruptions and climate change due to the dust layer formed in the atmosphere that covered the Sun. One of the youngest - Barringer Crater - is located in the desert of Arizona, USA. Its diameter is 1200 meters, depth is 175 meters. It arose 50 thousand years ago as a result of the impact of an iron meteorite with a diameter of about 50 meters and a mass of several hundred thousand tons.

In total, there are now about 170 impact craters formed by the fall of celestial bodies. The event near Chelyabinsk attracted the most attention, when on February 15, 2013, an asteroid entered the atmosphere in this area, the size of which was estimated at about 17 meters and a mass of 13,000 tons. It exploded in the air at an altitude of 20 kilometers, its largest part weighing 600 kilograms fell into Lake Chebarkul.

Its fall did not lead to casualties, the destruction was noticeable, but not catastrophic: glass was broken on a rather vast territory, the roof of the Chelyabinsk zinc plant collapsed, about 1,500 people were injured by glass fragments. It is believed that the catastrophe did not happen due to the element of luck: the trajectory of the fall of the meteorite was gentle, otherwise the consequences would have been much more difficult. The energy of the explosion is equivalent to 0.5 megatons of TNT, which corresponds to 30 bombs dropped on Hiroshima. Chelyabinsk asteroid became the most detailed event of this magnitude since the explosion Tunguska meteorite June 17 (30), 1908. According to modern estimates, the fall of celestial bodies, like Chelyabinsk, around the world occurs about once every 100 years. As for the Tunguska event, when trees were burned and felled over an area of ​​50 kilometers in diameter as a result of an explosion at an altitude of 18 kilometers with an energy of 10–15 megatons of TNT, such disasters happen about once every 300 years. However, there are cases when smaller bodies, colliding with the Earth more often than those mentioned, caused noticeable damage. An example is a four-meter asteroid that fell in Sikhote-Alin northeast of Vladivostok on February 12, 1947. Although the asteroid was small, it was composed almost entirely of iron and turned out to be the largest iron meteorites ever observed on the surface of the Earth. At an altitude of 5 kilometers, it exploded, and the flash was brighter than the Sun. The territory of the epicenter of the explosion (its projection on earth's surface) was uninhabited, but the forest was damaged on an area with a diameter of 2 kilometers and more than a hundred craters with a diameter of up to 26 meters were formed. If such an object fell on Big City hundreds and even thousands of people would have died.

At the same time, it is quite obvious that the probability of death of a particular person as a result of an asteroid fall is very low. This does not exclude the possibility that hundreds of years may pass without significant casualties, and then the fall of a large asteroid will lead to the death of millions of people. In table. 1 shows the probabilities of an asteroid impact, correlated with the mortality rate from other events.

It is not known when the next asteroid impact will occur, comparable or more severe in its consequences to the Chelyabinsk event. It may fall in 20 years, and in several centuries, but it may also tomorrow. Getting early warning of an event like the Chelyabinsk event is not only desirable - it is necessary to effectively deflect potentially dangerous objects larger than, say, 50 meters. As for collisions with the Earth of smaller asteroids, these events happen more often than we think: about once every two weeks. This is illustrated by the above map of the fall of asteroids measuring a meter or more over the past twenty years, prepared by NASA.

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Methods for deflecting potentially hazardous near-Earth objects

The discovery in 2004 of the asteroid Apophis, whose probability of collision with the Earth in 2036 was then considered quite high, led to a significant increase in interest in the problem of asteroid-comet defense. Work was launched to detect and catalog dangerous celestial objects, and research programs were launched to solve the problem of preventing their collisions with the Earth. As a result, the number of asteroids and comets found has increased dramatically, so that by now there are more of them discovered than was known before the start of work on the program. and various ways deviations of asteroids from the trajectories of impact with the Earth, including rather exotic ones. For example, coating the surfaces of dangerous asteroids with paint that will change their reflective characteristics, leading to the required deflection of the asteroid's trajectory due to the pressure of sunlight. Research continued on ways to change the trajectories of dangerous objects by colliding spacecraft with them. The latter methods seem to be quite promising and do not require the use of technologies that go beyond the capabilities of modern rocket and space technology. However, their effectiveness is limited by the mass of the homing spacecraft. For the most powerful Russian carrier Proton-M, it cannot exceed 5-6 tons.

Let us estimate the change in speed, for example, of Apophis, whose mass is about 40 million tons: a collision with it by a spacecraft weighing 5 tons at a relative speed of 10 km / s will give 1.25 millimeters per second. If the strike is delivered long before the expected collision, it is possible to create the required deflection, but this “long time” will be many decades. It is currently impossible to predict the asteroid's trajectory so far with acceptable accuracy, especially considering that there is uncertainty in knowing the parameters of the impact dynamics and, consequently, in estimating the expected change in the asteroid's velocity vector. Thus, in order to deflect a dangerous asteroid from a collision with the Earth, it is required to find an opportunity to direct a more massive projectile at it. As such, we can offer another asteroid with a mass significantly exceeding the mass of the spacecraft, say 1500 tons. But to control the movement of such an asteroid, too much fuel would be needed to put the idea into practice. Therefore, for the required change in the trajectory of the asteroid projectile, it was proposed to use the so-called gravitational maneuver, which does not require any fuel consumption in itself.

Under the gravitational maneuver understand the flight space object(in our case - a projectile asteroid) a fairly massive body - the Earth, Venus, other planets of the solar system, as well as their satellites. The meaning of the maneuver lies in such a choice of trajectory parameters relative to the body being flown (height, initial position and the velocity vector), which will allow, due to its gravitational influence, to change the orbit of an object (in our case, an asteroid) around the Sun so that it will be on the collision trajectory. In other words, instead of imparting a speed impulse to a controlled object with the help of a rocket engine, we receive this impulse due to the attraction of the planet, or, as it is also called, the sling effect. Moreover, the magnitude of the impulse can be significant - 5 km / s or more. To create it with a standard rocket engine, it is necessary to spend an amount of fuel that is 3.5 times more mass device. And for the gravitational maneuver method, fuel is needed only to bring the device to the calculated maneuver trajectory, which reduces its consumption by two orders of magnitude. It should be noted that this method of changing the orbits of spacecraft is not new: it was proposed in the early thirties of the last century by the pioneer of the Soviet rocket technology F. Zander. At present, this technique is widely used in the practice of space flights. Suffice it to mention once again, for example, the European spacecraft Rosetta: in the course of a ten-year mission, it performed three gravitational maneuvers near the Earth and one near Mars. One can recall the Soviet spacecraft Vega-1 and Vega-2, which first circled Halley's comet - on the way to it they performed gravitational maneuvers using the gravitational field of Venus. To reach Pluto in 2015, NASA's New Horizons spacecraft used a maneuver in Jupiter's field. The list of missions using gravity assist is far from exhaustive with these examples.

The use of a gravitational maneuver to guide relatively small near-Earth asteroids to dangerous celestial objects to deviate from the trajectory of a collision with the Earth was proposed by the staff of the Space Research Institute of the Russian Academy of Sciences at an international conference on the problem of asteroid hazard, organized in Malta in 2009. And in next year there was a journal publication outlining this concept and its justification.

To confirm the feasibility of the concept, the asteroid Apophis was chosen as an example of a dangerous celestial object.

Initially, they accepted the condition that the danger of an asteroid is established approximately ten years before its alleged collision with the Earth. Accordingly, the scenario of the asteroid's deviation from the trajectory passing through it was built. First of all, from the list of near-Earth asteroids whose orbits are known, one was chosen, which will be transferred to the vicinity of the Earth into an orbit suitable for performing a gravitational maneuver that ensures that the asteroid hits Apophis no later than 2035. As a selection criterion, we took the magnitude of the velocity impulse that must be communicated to the asteroid in order to transfer it to such a trajectory. The maximum allowable impulse was 20 m/s. Next, a numerical analysis of possible operations to guide the asteroid to Apophis was carried out in accordance with the following flight scenario.

After launching the head unit of the Proton-M launch vehicle into low Earth orbit with the help of the Breeze-M upper stage, the spacecraft is transferred to the trajectory of the flight to the projectile asteroid with subsequent landing on its surface. The device is fixed on the surface and moves along with the asteroid to the point where it turns on the engine, imparting an impulse to the asteroid, transferring it to the calculated trajectory of the gravitational maneuver - flying around the Earth. In the process of motion, the necessary measurements are taken to determine the motion parameters of both the target asteroid and the projectile asteroid. Based on the measurement results, the projectile trajectory is calculated and corrected. With the help of the propulsion system of the apparatus, the asteroid is given velocity impulses that correct errors in the parameters of the trajectory of movement towards the target. The same operations are performed on the trajectory of the spacecraft's flight to the projectile asteroid. The key parameter in developing and optimizing the scenario is the velocity impulse that must be imparted to the projectile asteroid. For candidates for this role, the dates of the message of the impulse, the arrival of the asteroid to the Earth and the collision with dangerous object. These parameters are selected in such a way that the momentum imparted to the projectile asteroid is minimal. In the process of research, the entire list of asteroids was analyzed as candidates, the orbital parameters of which are currently known - there are about 11,000 of them.

As a result of calculations, five asteroids were found, the characteristics of which, including sizes, are given in Table. 2. It was hit by asteroids, the dimensions of which significantly exceed the values ​​corresponding to the maximum allowable mass: 1500–2000 tons. In this connection, two remarks must be made. First, a far from complete list of near-Earth asteroids (11,000) was used for the analysis, while, according to modern estimates, there are at least 100,000 of them. boulders on its surface, the mass of which fits within the indicated limits (we can recall the asteroid Itokawa). Note that it is precisely this approach that is assessed as realistic in the American project for the delivery of a small asteroid to the lunar orbit. From Table. 2 it can be seen that the smallest velocity impulse - only 2.38 m/s - is necessary if the asteroid 2006 XV4 is used as a projectile. True, he himself is too big and exceeds the estimated limit of 1500 tons. But if you use its fragment or boulder on the surface with such a mass (if any), then the indicated impulse will create a standard rocket engine with a gas exhaust velocity of 3200 m/s, spending 1.2 tons of fuel. As calculations have shown, it is possible to land an apparatus on the surface of this asteroid with total weight more than 4.5 tons, so the delivery of fuel will not create problems. And the use of an electric rocket engine will reduce fuel consumption (more precisely, the working fluid) to 110 kilograms.

However, it should be taken into account that the data given in the table on the required speed impulses refer to the ideal case, when the required change in the speed vector is realized absolutely exactly. In fact, this is not the case, and, as already noted, it is necessary to have a supply of working fluid for orbit corrections. With the accuracies achieved so far, the correction may require a total of up to 30 m/s, which exceeds the nominal values ​​​​of the magnitude of the change in speed to solve the problem of intercepting a dangerous object.

In our case, when the controlled object has a mass three orders of magnitude larger, a different solution is required. It exists - this is the use of an electric rocket engine, which makes it possible to reduce the consumption of the working fluid by a factor of ten for the same corrective impulse. In addition, to improve the accuracy of guidance, it is proposed to use a navigation system that includes a small apparatus equipped with a transceiver, which is placed in advance on the surface of a dangerous asteroid, and two sub-satellites accompanying the main apparatus. With the help of transceivers, the distance between the devices and their relative speeds are measured. Such a system makes it possible to ensure that the asteroid-projectile hits the target with a deviation within 50 meters, provided that a small chemical engine with a thrust of several tens of kilograms is used in the last phase of the approach to the target, producing a speed impulse within 2 m/s.

Of the issues that arise when discussing the feasibility of the concept of using small asteroids to deflect dangerous objects, the question of the risk of an asteroid colliding with the Earth, transferred to the trajectory of a gravitational maneuver around it, is essential. In table. 2 shows the distances of asteroids from the center of the Earth at perigee when performing a gravitational maneuver. For four, they exceed 15,000 kilometers, and for asteroid 1994, GV is 7427.54 kilometers ( average radius Earth - 6371 kilometers). The distances look safe, but there is still no guarantee that there is no risk if the size of the asteroid is such that it can reach the Earth's surface without burning up in the atmosphere. How extreme allowable size consider a diameter of 8–10 meters, provided that the asteroid is not iron. A radical way to solve the problem is to use Mars or Venus to maneuver.

Capturing asteroids for research

The basic idea of ​​the Asteroid Redirect Mission (ARM) project is to transfer an asteroid to another orbit, more convenient for research with direct human participation. As such, an orbit close to the lunar one was proposed. As another option for changing the asteroid orbit, IKI RAS considered methods for controlling the movement of asteroids using gravity maneuvers near the Earth, similar to those that were developed to guide small asteroids to dangerous near-Earth objects.

The goal of such maneuvers is to transfer asteroids to orbits that are resonant with the orbital motion of the Earth, in particular, with the ratio of the periods of the asteroid and the Earth 1:1. Among the near-Earth asteroids, there are thirteen that can be transferred to resonant orbits in the indicated ratio and at a lower allowable limit perigee radius - 6700 kilometers. To do this, it is enough for any of them to report a speed impulse not exceeding 20 m/s. Their list is presented in Table. 3, where the magnitudes of the velocity impulses are indicated, transferring the asteroid to the trajectory of the gravitational maneuver near the Earth, as a result of which the period of its orbit becomes equal to the earth, that is, one year. The maximum and minimum achievable speeds of the asteroid in its heliocentric motion are also given there. It is interesting to note that the maximum speeds can be very high, allowing the maneuver to throw the asteroid quite far from the Sun. For example, the asteroid 2012 VE77 can be sent into an orbit with an aphelion at a distance from the orbit of Saturn, and the rest - beyond the orbit of Mars.

The advantage of resonant asteroids is that they return to the vicinity of the Earth every year. This makes it possible at least every year to send a spacecraft to land on an asteroid and deliver soil samples to Earth, and almost no fuel is required to return the descent vehicle to Earth. In this regard, an asteroid in a resonant orbit has advantages over an asteroid in a lunar orbit, as planned in the Keck project, since it requires a noticeable fuel consumption to return. For unmanned missions, this can be decisive, but for manned flights, when it is necessary to ensure that the device returns to Earth as quickly as possible in an emergency (within a week or even earlier), the advantage may be on the side of the ARM project.

On the other hand, the annual return of resonant asteroids to the Earth allows periodic gravitational maneuvers, each time changing their orbit to optimize research conditions. In this case, the orbit must remain resonant, which is easy to implement by performing multiple gravity maneuvers. Using this approach, it is possible to transfer the asteroid to an orbit identical to the Earth, but slightly inclined to its plane (to the ecliptic). Then the asteroid will approach the Earth twice a year. The family of orbits resulting from a sequence of gravity maneuvers includes an orbit whose plane lies in the ecliptic, but has a very large eccentricity and, like the asteroid 2012 VE77, reaches the orbit of Mars.

If we further develop the technology of gravitational maneuvers for planets, including the construction of resonant orbits, then the idea arises to use the Moon. The fact is that the gravitational maneuver of the planet in pure form does not allow capturing an object into the satellite's orbit, since the energy of its relative motion does not change when flying around the planet. If at the same time it flies around the natural satellite of the planet (the Moon), then its energy can be reduced. The problem is that the reduction should be sufficient to transfer to the satellite's orbit, that is, the initial velocity relative to the planet should be small. If this requirement is not met, the object will leave the vicinity of the Earth forever. But if you choose the geometry of the combined maneuver so that as a result the asteroid remains in a resonant orbit, then in a year you can repeat the maneuver. Thus, it is possible to capture an asteroid into the orbit of the Earth's satellite by applying gravity maneuvers near the Earth while maintaining the resonance condition and coordinated flyby of the Moon.

Obviously, individual examples confirming the possibility of implementing the concept of controlling the movement of asteroids using gravitational maneuvers do not guarantee a solution to the problem of asteroid-comet hazard for any celestial object, collision threatening with the earth. It may happen that in a particular case there is no suitable asteroid that can be directed at it. But, as shown latest results Calculations carried out taking into account the “freshest” cataloged asteroids, with the maximum allowable velocity impulse required to transfer an asteroid to the planet’s vicinity equal to 40 m/s, the number of suitable asteroids is 29, 193 and 72 for Venus, Earth and Mars, respectively. They are included in the list of celestial bodies, the movement of which can be controlled by means of modern rocket and space technology. The list is rapidly growing, as two to five asteroids are currently discovered on average per day. So, for the period from November 1 to November 21, 2014, 58 near-Earth asteroids were discovered. Until now, we could not influence the movement of natural celestial bodies, but a new phase in the development of civilization is beginning, when this becomes possible.

Glossary for the article

Bode's law(the Titius-Bode rule, established in 1766 by the German mathematician Johann Titius and reformulated in 1772 by the German astronomer Johann Bode) describes the distances between the orbits of the planets of the solar system and the Sun, as well as between the planets and the orbits of its natural satellites. One of his mathematical formulations: R i = (D i + 4)/10, where D i = 0, 3, 6, 12 ... n, 2n, and R i is the average radius of the planet's orbit in astronomical units (a. e.).

This empirical law holds for most planets with an accuracy of 3%, but it seems to have no physical meaning. There is, however, an assumption that at the stage of formation of the Solar System, as a result of gravitational perturbations, a regular ring structure of regions arose in which the orbits of protoplanets turned out to be stable. Later studies of the solar system showed that Bode's law, generally speaking, is far from always being fulfilled: the orbits of Neptune and Pluto, for example, are much closer to the Sun than he predicts (see table).

(L-points, or libration points, from lat. Libration- swinging) - points in the system of two massive bodies, for example, the Sun and a planet or a planet and its natural satellite. A body of significantly smaller mass - an asteroid or space laboratory- will remain at any of the Lagrange points, making oscillations of small amplitude, provided that only gravitational forces act on it.

The Lagrange points lie in the plane of the orbit of both bodies and are designated by indices from 1 to 5. The first three - collinear - lie on a straight line connecting the centers of massive bodies. Point L 1 is located between massive bodies, L 2 - behind the less massive, L 3 - behind the more massive. The position of the asteroid at these points is the least stable. Points L 4 and L 5 - triangular, or Trojan - are in orbit on both sides of the line connecting the bodies of large mass, at angles of 60 about from the line connecting them (for example, the Sun and the Earth).

Point L 1 of the Earth-Moon system is a convenient place for placing a manned orbital station that allows astronauts to get to the Moon with minimal fuel costs, or an observatory for observing the Sun, which at this point is never obscured by either the Earth or the Moon.

Point L 2 of the Sun-Earth system is convenient for building space observatories and telescopes. The object at this point retains its orientation relative to the Earth and the Sun indefinitely. It already houses the American laboratories Planck, Herschel, WMAP, Gaia and others.

At the point L 3, on the other side of the Sun, science fiction writers have repeatedly placed a certain planet - the Counter-Earth, which either arrived from afar, or was created simultaneously with the Earth. Modern observations have not detected it.

Eccentricity(Fig. 1) - a number characterizing the shape of a second-order curve (ellipse, parabola and hyperbola). Mathematically, it is equal to the ratio of the distance of any point of the curve to its focus to the distance from this point to the straight line, called the directrix. Ellipses - the orbits of asteroids and most other celestial bodies - have two directrixes. Their equations are: x = ±(a/e), where a is the semi-major axis of the ellipse; e - eccentricity - a constant value for any given curve. The eccentricity of the ellipse is less than 1 (for a parabola, e \u003d 1, for a hyperbola, e\u003e 1); when e > 0, the shape of the ellipse approaches a circle; when e > 1, the ellipse becomes more and more elongated and compressed, degenerating into a segment in the limit - its own major axis 2a. Another, simpler and more visual definition of the eccentricity of an ellipse is the ratio of the difference between its maximum and minimum distances to the focus to their sum, that is, the length of the major axis of the ellipse. For circumsolar orbits, this is the ratio of the difference in the distance of a celestial body from the Sun at aphelion and perihelion to their sum (major axis of the orbit).

sunny wind - constant flow plasma solar corona, that is, charged particles (protons, electrons, helium nuclei, oxygen ions, silicon, iron, sulfur) in radial directions from the Sun. It occupies a spherical volume with a radius of at least 100 AU. That is, the boundary of the volume is determined by the equality of the dynamic pressure of the solar wind and the pressure of the interstellar gas, magnetic field Galaxy and galactic cosmic rays.

Ecliptic(from Greek. ekleipsis- eclipse) - great circle celestial sphere, along which the apparent annual motion of the Sun occurs. In reality, since the Earth moves around the Sun, the ecliptic is a section of the celestial sphere by the plane of the Earth's orbit. The ecliptic line runs through the 12 constellations of the zodiac. Its Greek name is due to the fact that it has been known since antiquity that solar and lunar eclipses occur when the Moon is near the point of intersection of its orbit with the ecliptic.

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Translated from Greek, an asteroid sounds like "similar to a star." These are small celestial bodies compared to the planets, moving in orbit around the Sun. Asteroids are predominantly composed of various metals and rocks.

Pallas

Daughter of the ancient Greek god Triton. The asteroid was discovered on March 28, 1802 by the German astronomer Heinrich Wilhelm Olbers. It happened in Bremen (Germany). The dimensions of the asteroid are 582x556x500 km, density 2.7 g/cm3, rotation period 7.81 hours,
surface temperature -109 °C.

Juno

Ancient Roman goddess, wife of Jupiter; goddess of marriage, birth and motherhood. The asteroid was discovered on September 1, 1804 by the German astronomer Carl Ludwig Harding. This happened at the Lilienthal Observatory, (Lilienthal, Germany). The dimensions of the asteroid are 320x267x200 km, density 2.98 g/cm3, rotation period 7.21 hours, surface temperature -110 °C.

Vesta

Ancient Roman goddess, patroness of the family hearth and sacrificial fire. The asteroid was discovered on March 29, 1807 by the German astronomer Heinrich Wilhelm Olbers. It happened in Bremen, Germany. The dimensions of the asteroid are 578 x 560 x 458 km, density 3.5 g/cm3, rotation period 5.34 hours, surface temperature -95 °C.

astrea

Ancient Greek goddess of justice, daughter of Zeus and Themis. The asteroid was discovered on December 8, 1845 by the German astronomer Carl Ludwig Henke. It happened in Drezdenko (Poland). The dimensions of the asteroid are 167x123x82 km, density 2.7 g/cm3, rotation period 0.7 days, surface temperature -106 °C.

Hebe

Ancient Greek goddess of youth, daughter of Zeus and Hera. The asteroid was discovered on July 1, 1847 by the German astronomer Carl Ludwig Henke. It happened in Drezdenko (Poland). The dimensions of the asteroid are 205x185x170 km, density 3.81 g/cm3, rotation period 0.303 days, surface temperature -103 °C.

Irida

Ancient Greek goddess of the rainbow, daughter of Taumantus and Electra. The asteroid was discovered on August 13, 1847 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The dimensions of the asteroid are 240x200x200 km, density 3.81 g/cm3, rotation period 0.2975 days, surface temperature -102 °C.

Flora

Ancient Roman goddess of flowers and spring. The asteroid was discovered on October 18, 1847 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The dimensions of the asteroid are 136x136x113 km, density 3.13 g/cm3, rotation period 0.533 days, surface temperature -93 °C.

methyl

Ancient Greek goddess of wisdom. The asteroid was discovered on April 25, 1848 by Irish astronomer Andrew Graham. This happened at the Markry Observatory (County Sligo, Ireland). The dimensions of the asteroid are 222x182x130 km, density 4.12 g/cm3, rotation period 0.2116 days, surface temperature 100 "C.

Hygiea

Ancient Greek goddess of health. The asteroid was discovered on April 12, 1849 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The dimensions of the asteroid are 530x407x370 km, density 2.08 g/cm3, rotation period 27.623 hours, surface temperature -109 °C.

Parthenope

Siren, who founded the city of Parthenope, currently Naples. The asteroid was discovered on May 11, 1850 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The diameter of the asteroid is 153.3 km, the density is 3.28 g/cm3, the rotation period is 9.43 hours, and the surface temperature is -99 °C.

Victoria

Ancient Greek goddess of health. The asteroid was discovered on September 13, 1850 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The diameter of the asteroid is 112.8 km, the density is 2 g/cm3, the rotation period is 8.66 hours, and the surface temperature is -95°C.

Egeria

Ancient Roman water nymph. The asteroid was discovered on November 2, 1850 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The diameter of the asteroid is 207.64 km, the density is 3.46 g/cm3, the rotation period is 7.04 hours, and the surface temperature is -99 °C.

Irena

Ancient Greek goddess of peace. The asteroid was discovered on September 13, 1850 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The diameter of the asteroid is 152 km, the density is 4.42 g/cm3, the rotation period is 15.06 hours, and the surface temperature is -198 °C.

Eunomia

Ancient Greek ora, daughter of Zeus and Themis. The asteroid was discovered on July 29, 1851 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The dimensions of the asteroid are 357x255x212 km, density 3.09 g/cm3, rotation period 6.083 hours, surface temperature -107 °C.

Psyche

Personifications of the soul ancient Greek mythology. The asteroid was discovered on March 17, 1852 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The dimensions of the asteroid are 240x185x145 km, density 6.49 g/cm3, rotation period 4.196 hours, surface temperature -113 °C.

Thetis

Nereid, daughter of Nereus and Dorida. The asteroid was discovered on April 17, 1852 by the German astronomer Robert Luther. This happened at the Düsseldorf Observatory (Düsseldorf, Germany). The diameter of the asteroid is 90 km, the density is 3.21 g/cm3, the rotation period is 12.27 hours, and the surface temperature is -100 °C.

Melpomene

Ancient Greek muse of tragedy. The asteroid was discovered on June 24, 1852 by the English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The dimensions of the asteroid are 170x155x129 km, density 1.69 g/cm3, rotation period 11.57 hours, surface temperature -96 °C.

Fortune

Ancient Roman goddess of fortune. The asteroid was discovered on September 13, 1850 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The dimensions of the asteroid are 225x205x195 km, density 2.70 g/cm3, rotation period 7.44 hours, surface temperature -93 °C.

massadiya

Greek name for the French city of Marseille. The asteroid was discovered on September 19, 1852 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The dimensions of the asteroid are 160x145x132 km, density 3.54 g/cm3, rotation period 8.098 hours, surface temperature -99 °C.

Lutetia

Latin name of the French city of Paris. The asteroid was discovered on September 13, 1850 by German-French astronomer Hermann Goldschmidt. This happened in the dimensions of the asteroid 132x101x76 km, density 3.4 g/cm3, rotation period 8.16 hours, surface temperature -101 °C.

calliope

Ancient Greek muse of epic poetry. The asteroid was discovered on November 16, 1852 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The dimensions of the asteroid are 235x144x124 km;

Waist

Ancient Greek muse of comedy and light poetry. The asteroid was discovered on December 15, 1852 by English astronomer John Russell Hynde. This happened at the Bishop Observatory (London, England). The diameter of the asteroid is 107.5 km, the density is 2 g/cm3, the rotation period is 12.308 hours, and the surface temperature is -109 °C.

Themis

Ancient Greek goddess of justice. The asteroid was discovered on April 5, 1853 by the Italian astronomer Annibale de Gasparis. This happened at the Capodimonte Observatory (Naples, Italy). The asteroid has a diameter of 107.5 km, a density of 2.78 g/cm3, a rotation period of 8 hours and 23 minutes, and a surface temperature of -114°C.

For a couple of sleepless nights, I dashed off a story about how asteroids were called and are called. IMHO, an interesting story both in terms of the development of astronomy, and in terms of demonstrating that even in such an accurate and noble science, not everything goes smoothly.

To begin with, let me remind you of the basic things. Asteroids (the term was introduced by William Herschel in 1802) or minor planets are called small bodies of the solar system (not large enough to be considered a planet, but more than thirty meters, smaller objects are called meteoroids), revolving around the Sun and not being comets (comets are characterized by gas-forming activity when approaching the Sun; in this case, individual asteroids are, in fact, "degenerate", "extinct" comets).

Ceres was the first asteroid to be discovered (it was discovered on January 1, 1801). At first, it was considered a full-fledged planet (occupying a position between Mars and Jupiter), then it became clear that it was only one of the representatives of a large group of celestial bodies, and already in 2006 it was reclassified as a dwarf planet. Subsequent asteroids were discovered in 1802 (Pallas), 1804 (Juno) and 1807 (Vesta). Then there was a break until 1845 (when Astrea was discovered), and from 1847 asteroids began to be discovered several times a year. By the beginning of the 20th century, more than four and a half hundred asteroids were already known; it is clear that in the future the frequency of their discoveries constantly increased, at the end of the 20th century this growth became explosive. As of July 9, 2017, 734274 asteroids are known, of which 496815 have constant numbers (that is, their orbit is considered to be reliably calculated), while only 21009 asteroids have their own names (infa from the Minor Planet Center).

Image taken from here: https://commons.wikimedia.org/wiki/File:Minor_planet_count.svg

It is clear that the designation and naming of asteroids is a rather serious problem (since the number of asteroids is so large). I will try to tell you about the solutions to this problem. The bulk of the text is based on the book Schmadel, Lutz D. Dictionary of Minor Planet Names. - Fifth Revised and Enlarged Edition. - B., Heidelberg, N. Y.: Springer, 2003. - P. 298. - ISBN 3-540-00238-3 (not a translation, but a free retelling), plus information from Wikipedia was involved. For those who are interested, read on.

Formal designations of asteroids

Before mid-nineteenth For centuries, there has been no nomenclature problem with regard to asteroids. Ceres, Pallas, Juno and Vesta (the first discovered asteroids) were mentioned simply by their names. The problem arose only around the 1850s due to a significant increase in the number of discovered asteroids. At first it seemed possible to simply give each asteroid given name and create a separate astronomical symbol for each of them (that is, act in the same way as they previously did with large planets). However, the practice of awarding symbols quickly proved to be untenable. The use of these symbols turned out to be both difficult from the point of view of publishing technology, and completely impractical from the point of view of memory load (remembering all these symbols, given the further growth in their number, seemed impossible). Most likely, last astronomer, which assigned a separate symbol to the asteroid (namely, the asteroid (32) Fidesz), was Carl Theodor Robert Luther (Luther, 1855).

Instead of using symbols, a system of ordinal numbers was introduced. For the first time, such an idea (with the placement of the asteroid serial number in a circle) was expressed by Johann Franz Enke (Enke, 1851) on the pages of "Berliner astronomisches Jahrbuch" (hereinafter - BAJ). The first practical application of this system belongs to the American astronomer James Ferguson (Ferguson, 1852), who designated Psyche as ⑯ Psyche(the asteroid Psyche was discovered in 1852; at present, the serial number of the asteroid is placed in parentheses - (16) Psyche). The serial number was awarded by the editor of the journal "Astronomische Nachrichten" (hereinafter - AN) corresponding to the date of the first publication of the discovery of a new asteroid, which soon led to unpleasant contradictions: for example, in early October 1857, Ferguson discovered the asteroid Virginia, which was assigned the serial number 50, while the asteroid discovered by Goldschmidt back in September of the same year (Meleta) , was assigned the serial number 56. The astronomical community came to the conclusion that the assignment of a proper name to astroids can be postponed for some time, while the tradition of awarding serial numbers strictly in accordance with the chronology of discoveries must be strictly observed.

The issues of naming and assigning serial numbers were further complicated by the fact that it was difficult to judge who exactly was considered the discoverer and who exactly had the right to give a name to a new asteroid. Rudolf Wolf (Wolf, 1859) owns the following remark: “The discovery of Uranus cannot be attributed to Flamsteed, the discovery of Neptune cannot be attributed to Lalande, in the same way the discovery of asteroid-56 cannot be attributed to Goldschmidt: the discoverer of the planet is not the one who first saw it or observed, and the one who first recognized in it a new celestial object". Cases when the first observer did not realize the nature of the observed object, and the main role in the discovery belonged to the person who first calculated the orbit of a new body, were already frequent then. Questions related to these details remain relevant to this day.

A natural color image of Ceres taken by the Dawn spacecraft on May 4, 2015.

The rapid increase in the number of new asteroid discoveries has forced the editors of the journals BAJ and AN to award serial numbers as soon as possible, according to the dates of discoveries. Although the idea of ​​a strict correspondence between serial numbers and the chronology of discoveries was not objectionable, the rapid increase in the number of newly discovered asteroids soon gave rise to new difficulties. A significant number of new asteroids have been observed only sporadically, without confident calculation and confirmation of their orbits - what should have been done with them? To award them any serial numbers or not? Adalbert Kruger (Kruger, 1892) proposed the following system: “From now on, the editor of the AN will assign to each new planet [meaning asteroids] a temporary designation of the following form: 18xx A, B, C ... according to the date of registration [discovery report] in the Central Bureau of Astronomical Telegram. The final serial number will be awarded only later by the BAJ editor. This will eliminate the assignment of serial numbers to those planets [i.e. e., asteroids] whose orbital elements cannot be calculated due to lack of data.” That is, the first asteroid, supposedly discovered in 1893, received the temporary designation 1893 A, the second discovered in the same year - 1893 B, and so on. However, a year later, in 1893, it became clear that capital letters alone would not be enough, and therefore it was decided to expand this system by doubling the letters: for example, the asteroid 1893 Z was to be followed by the asteroid 1893 AA, followed by 1893 AB, and so on. The system was adopted, but it should be noted that during the First World War, separate "unofficial" systems were also used; in particular, the astronomers of the Simeiz Observatory (this is the one we have in Crimea), who for some time worked without a reliable connection with the rest of the astronomical world, were forced to introduce their own system of temporary numbering of new asteroids.

In 1924 (taking into account the ever-increasing number of newly discovered asteroids), a new system of temporary designations was proposed: first comes the year of discovery, and after the space, the Latin letter denoting the crescent of discovery (A - for the first half of January, B - for the second half of January, C - for the first half of February and so on, excluding the letter I, since it can be confused with a unit); it is joined by another Latin letter, denoting the order of opening in the corresponding crescent (again, excluding the letter I). So, for example, the designation 1926 AD means that the asteroid was discovered fourth in a row in the first half of January 1926, and the designation 1927 DG means that the asteroid was discovered seventh in a row in the second half of February 1927. Almost immediately (Kopff, 1924) this system was further extended to current state (« on that incredible case (sic!!!) - as August Kopff himself wrote - if more than 25 asteroids are discovered in a crescent”): now, if more than 25 minor planets are discovered in a crescent (26 letters of the Latin alphabet minus one, I is not used), then a digital index is added to the designation, which shows how many times the alphabetic sequence in the second position was used (thus the number of discoveries in this half of the month is determined by multiplying the index by 25 plus the serial number of the second letter in the asteroid designation). That is, the twenty-fifth asteroid discovered in the first half of January 1950 will receive the designation 1950 AZ, while the next (26th) will receive the designation 1950 AA 1 , the 27th - 1950 AB 1 , the 51st - 1950 AA 2 and etc. Test your ingenuity and answer the question: in which crescent and in what order in this crescent was the celestial body 2003 VB 12 discovered? I will give the correct answer at the very end of the post :).

Since 1952, according to the proposal of the American astronomer Paul Herget, permanent (final) serial numbers have been awarded only if a number of conditions are met (Herget, 1952). The orbital parameters of these objects had to be calculated:
a) based on observations at at least two oppositions (this requirement can be excluded if the perihelion distance of the observed body is less than 1.67 AU);
b) taking into account perturbations;
c) satisfying all the observations made so far.

As time passed, the requirements for assigning a permanent serial number became even more stringent: with the exception of objects with rather unusual orbits or those that could approach the Earth, careful observation of the object in at least three oppositions was already required to assign a permanent number. In 1991, the American astronomer Brian Marsden (then head of the Center for Minor Planets - today the central organization that systematizes data on new discovered bodies of the Solar System) put forward a requirement for even four or more observations in opposition to assign a constant serial number (excluding objects approaching with the Earth or constantly confidently observed).

Development of asteroid naming traditions

The names of the first asteroids (Ceres, Pallas, Juno and Vesta) followed the classical tradition, according to which the celestial bodies were named after ancient (Greek and Roman) gods or mythological characters. At first it seemed that this tradition would be unshakable, but the name of the twelfth asteroid Victoria (discovered in 1850; formally the name corresponded to the Roman goddess of victory, but the astronomical community had serious suspicions that the discoverer, Briton John Russell Hynd, gave this name in honor of Queen Victoria) has given rise to discussions about whether it is acceptable to name asteroids after current rulers. One of the most active advocates for exclusively "classical" names was the German astronomer Karl Theodor Robert Luther (Luther, 1861), who postulated the following: "Since we consider it necessary to give our own names to stars, comets, satellites of Saturn and Uranus, and even mountains on the Moon, it seems reasonable to prefer names from classical mythology. Not classic names are unreasonable from the point of view of long-term use, it is better to use only numbering instead.

Such a dogmatic approach immediately met with harsh criticism. Karl August Steinheil (1861) argued with Luther: “What is the advantage of using only classical names? Are the new planets supposed to only remind us that we once attended a classical school? Does astronomy owe something so much to philology as to remember all these names?

An image of Vesta (the brightest of the asteroids) taken by the Dawn spacecraft in 2012.

Despite the fact that Luther's categorical approach met with many objections, the tendency to assign names from Greco-Roman mythology to newly discovered asteroids prevailed for quite a long time. Of course, there were many exceptions: the most striking example is the asteroid (45) Eugene, discovered in 1857 and named after the French Empress Eugenie de Montijo, wife of Napoleon III (the first time an asteroid was named after a living person). Asteroid (51) Nemause(opened in 1858) was named after the Latin name of the French city of Nimes. Asteroid (77) Frigga(opened in 1862) was named after Frigga, Odin's wife and supreme goddess in Germano-Scandinavian mythology. Asteroid (89) Julia(opened in 1866) was named after the Christian saint Julia of Corsican, who died in the 5th century. Asteroid (88) Thisbe was named after the heroine of the Babylonian legendarium (Pyramus and Thisbe - the Babylonian counterpart of Romeo and Juliet). And so on and so forth. Nevertheless, we note that even the names that did not have direct relation to Greco-Roman mythology, nevertheless, according to tradition, they were translated into the feminine form.

The struggle for exclusively "classic" names, however, continued. The same Luther in 1878 stated: “The current names of asteroids have become more than a mixture of different suits. It seems very appropriate to return to the old preferences, to the classical mythological names. All hints must be avoided - for the sake of the honor of our science. He was echoed by Heinrich Bruns (Bruhns, 1878): “The best solution seems to be to avoid any names that evoke associations with living people and current events. Only the classic names will be universally recognized.”

When the number of discovered asteroids exceeded four hundred, maintaining the "mythological" tradition became even more difficult than before. The unofficial but widely accepted rule for naming new asteroids was reduced to a requirement to use exclusively female names. Julius Bauschinger (Bauschinger, 1899; by the way, he was a consultant for Alfred Wegener's doctoral dissertation, who later put forward the theory of continental drift) when he was director of the Astronomisches Rechen-Institut, he even almost threatened: “There are reasons to ask the discoverers not to deviate from the tradition of using female names , since this rule was violated - for good reason - only once in relation to an asteroid (433) Eros. Male asteroid names will not be accepted by the BAJ." Heinrich Kreutz (Kreutz, 1899), who was then editor of the AN, also fully agreed with Bauschinger when he stated that male names would not be considered by the AN editors. It should be noted that the asteroid (433) Eros, discovered in 1898 by Karl Witt, really became the first asteroid with a classical male name, but he was then “forgiven” because his orbit turned out to be extremely unusual for the then ideas: if “classical asteroids” circulated only between the orbits of Mars and Jupiter, then Eros became the first discovered body from the group of "near-Earth asteroids", the perihelion of its orbit lies inside the orbit of Mars.

Asteroid Eros (a series of photographs taken by the NEAR spacecraft in 2000, showing its rotation).

The tradition of naming asteroids only by female names (even if woman's name created only artificially by adding endings -a or -ia) lasted quite a long time - until about the end of World War II (although it was repeatedly violated). For example, according to this tradition, asteroid 449 (discovered in 1899 and named after Hamburg) was named Hamburg, asteroid 662 (discovered in 1908 and named after the city of Newton, Massachusetts) was named newtonia, and asteroid 932, discovered in 1920 and named after Herbert Hoover, was named Hooveria, etc., there are many examples. The final departure from this tradition was declared in the Minor Planet Center Circular number 837 (1952): “The tradition of giving female endings to male names already has many exceptions. From now on, proposed names will not be rejected or modified if they have a masculine form."

current preferences regarding the naming of asteroids (it is difficult to call them directly rigid rules) were formulated in 1985. Now the following procedure works:
1. First, the newly discovered body is given a temporary alphanumeric designation (see above).
2. When the orbit of a new body is determined with sufficient confidence (as a rule, this requires the observation of an object at four or more oppositions), the Minor Planet Center awards it a permanent number.
3. After the award of a permanent serial number, the discoverer is invited to give the body its own name. The discoverer must accompany his name with a brief explanation of the reasons why he considers this name worthy of choice.
4. The proposed names are considered and approved by the working group of the International Astronomical Union on the nomenclature of small bodies.

The proposed names are subject to the following formal requirements (not always observed, but still highly desirable):
1. The name should not consist of more than 16 letters.
2. It is highly desirable that it should consist of one word.
3. The word must be pronounceable and make sense in at least some language (that is, just a random set of letters like Azzzxwfhu is likely to be rejected).
4. The name should not be offensive or cause unpleasant associations.
5. The new name should not be too similar to the existing names of other objects in the solar system.
6. Nicknames of pets are not approved (although there were precedents when asteroids were named in honor of the discoverers' pets).
7. Commercial type names ( trade marks etc.) are not allowed.
8. Names based on the names of politicians or related to any military actions are only allowed to be considered if 100 years have passed since the death of the character or event.
9. Unlike comets, asteroids are not automatically named after their discoverers (however, it was not uncommon for discoverers to name different asteroids after each other). However, there is an exception here: the astroid (96747) Crespodasilva was named after its discoverer, Lucy d'Escoffier Crespo da Silva, who committed suicide shortly after her discovery at age 22.

For naming individual groups asteroids (characterized by certain properties) still adhere to stricter traditions. For example, the so-called Trojan asteroids (which are in 1:1 resonance with Jupiter) are named after heroes Trojan War; trans-Neptunian objects with stable and long-lived orbits receive mythological names, one way or another connected with the creation of the world, etc.

The name becomes official after its promulgation in the Minor Planet Center circular. The International Astronomical Union does not award titles for money.

As of July 9, 2017, out of 734,274 known asteroids, 496,815 asteroids have been assigned definitive numbers, while only 21,009 of them have proper names (i.e., only four percent of the total number of asteroids with permanent numbers). Most of the names of asteroids consist of seven letters (information for 2003). The rule that the length of the name should not exceed 16 characters was violated once in the case of an asteroid (4015) Wilson-Harrington.

Interesting Facts

The first asteroid with a name not related to ancient mythology was (20) Massalia(opened in 1852 and named after the Greek name of the city of Marseille).

The first asteroid named after a living person was (45) Eugene(opened in 1857 and named after Napoleon III's wife Eugenia de Montijo).

The first man to have an asteroid named after him was Alexander von Humboldt: an asteroid was named after him (54) Alexandra, discovered in 1858 (it can be seen that the name of the asteroid was nevertheless given female form; in addition, it could be assumed that the name was given in honor of Alexandra, the daughter of the mythological king Priam, but the discoverer's intention was to name the asteroid in honor of Humboldt).

Although the names of pets are now considered "forbidden", there are precedents of this kind. Yes, asteroids. (482) Petrina and (483) Seppina named after the dogs (Peter and Sepp) of the discoverer M. F. Wolf (both asteroids were discovered in 1902). An asteroid discovered in 1971 was named (2309) Mr. Spock in honor of the discoverer's cat (the cat, in turn, got its nickname in honor of the character in the Star Trek television series).

Among the names of asteroids, you can also find such unusual ones as (4321) Zero(named after the nickname of American comedian Samuel Joel "Zero" Mostel) (6042) Cheshire Cat (named after an Alice in Wonderland character) (9007) James Bond(here the serial number of the asteroid played into the hands), (13579) Odd(in the original - Allodd, the ordinal number of the astroid consists of odd numbers, in ascending order), (24680) Odds(in the original - Alleven).

Photo of the asteroid Gaspra (named after the Crimean village), which became the first asteroid explored by a spacecraft (Galileo, 1991).

The names of asteroids are often adapted in individual national languages. So, the very first discovered asteroid (now considered a dwarf planet) we call Ceres, while many Western languages they call him Ceres, and the Greeks - and in general Demeter (Δήμητρα). The Greeks call Juno Hera, Vesta - Hestia, etc., according to the analogies between Greek and Roman mythology. AT Chinese the classical names of asteroids end with the hieroglyph 星 (star, celestial body), followed by the hieroglyph 神 (deity) or 女 (woman), and already before it - the hieroglyph describing the most characteristic property this deity. So, for example, Ceres is called in Chinese 穀神星 (that is, "the planet of the deity of cereals"), Pallas - 智神星 (that is, the "planet of the deity of wisdom"), etc.

There were three paradoxical cases where asteroids managed to get their own name even before receiving a permanent serial number (that is, before their orbit was reliably calculated). These are (1862) Apollo(opened in 1932, but received a permanent number only in 1973), (2101) Adonis(opened in 1936, but received a permanent number only in 1977) and (69230) Hermes(opened in 1937, but received a permanent number only in 2003). In the interval between the date of discovery and the date of assignment of a permanent number, these asteroids were considered "lost". "Lost", but later "re-found" asteroids, there are about two dozen. There are about 1-2 tens of thousands of asteroids that were observed for only a few days and finally lost (well, that is, still not found).

Despite the fact that the nomenclature of celestial bodies is, as it were, a very serious thing, it contains many examples of absurdities, oddities, and seemingly unacceptable coincidences. For example, many asteroids and satellites major planets have the same names: Europa (a moon of Jupiter) and an asteroid (52) Europe, Pandora (moon of Saturn) and an asteroid (55) Pandora etc. Sometimes the names are the same, but have a different origin: for example, an asteroid (218) Bianca was named after the Austrian opera singer Bianca (real name Berta Schwartz), and Uranus' moon Bianca was named after a character from Shakespeare's The Taming of the Shrew. Often the names are similar and in some languages ​​even "intersect": for example, the satellite of Jupiter Callisto in languages ​​using the Latin alphabet is designated as Callisto, while the asteroid (204) Callisto- already like Kallisto.

Finally, quite often asteroids have different names, but these names refer to the same referent (often we are talking about situations where analogues between Greek and Roman mythological characters were used for the name). So, in addition to the Moon (a satellite of the Earth), there is an asteroid (580) Selena(Selena is the Greek name for the Moon), the name of the asteroid (4341) Poseidon is the Greek equivalent of the Latin name for the planet Neptune. asteroids (433) Eros, (763) Cupid and (1221) Cupid refer to the same referent. Compare also (2063) Bacchus and (3671) Dionysus. Or here are more fun "crossings": (1125) China and (3789) Zhongguo (Zhongguo- the name of China in Chinese), (14335) Aleksosipov and (152217) Akosipov(both named after the Soviet and Ukrainian astronomer Alexander Osipov).

The answer to the riddle
To begin with, let me remind you the question: in which crescent and in what order was the celestial body with the temporary designation 2003 VB 12 discovered?

Answer: This asteroid was the 302nd asteroid discovered during the first half of November 2003. The opening year is clear. The first letter V indicates the first half of November (V is the 22nd letter of the Latin alphabet, but the letter I is not used in this system, 22 minus 1 gives 21, that is, this is the first half of the eleventh month). The digital index 12 shows that the sequence of twenty-five “second” letters (I remind you - I is not used) was repeated 12 times (that is, we multiply 12 by 25 and get 300). Next, we look at the second letter in the designation - B, the second letter of the Latin alphabet. We add 2 to 300 and we get 302. We are talking about the temporary designation assigned to the body, which is now better known as the trans-Neptunian object Sedna.

The shape and surface of the asteroid Ida.
North is up.
Animated by Typhoon Oner.
(Copyrighted © 1997 by A. Tayfun Oner).

1. General representations

Asteroids are solid rocky bodies that, like planets, move in elliptical orbits around the sun. But the sizes of these bodies are much smaller than those of ordinary planets, which is why they are also called minor planets. The diameters of asteroids range from several tens of meters (relatively) to 1000 km (the size of the largest asteroid Ceres). The term "asteroid" (or "stellar") was introduced 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 sources of light, although, like other planets, they themselves do not emit anything in the visible range, but only reflect the incident sunlight. The diameters of some asteroids have been measured using the "star occultation" method, at those fortunate moments when they were on the same line of sight with sufficiently bright stars. In most cases, their sizes are estimated using special astrophysical measurements and calculations. Most of the currently known asteroids move between the orbits of Mars and Jupiter at distances from the Sun of 2.2-3.2 astronomical units (hereinafter referred to as AU). In total, about 20,000 asteroids have been discovered to date, of which about 10,000 are registered, that is, they are assigned numbers or even proper names, and the orbits are calculated with great accuracy. Proper names for asteroids are usually assigned by their discoverers, but in accordance with established international rules. In the beginning, when the minor planets were known a little more, their names were taken, as for other planets, from ancient Greek mythology. The annular region of space occupied by these bodies is called the main asteroid belt. With an average linear orbital speed about 20 km / s, the asteroids of the main belt spend from 3 to 9 Earth years per revolution around the Sun, depending on the distance from it. The inclinations of the planes of their orbits with respect to the plane of the ecliptic sometimes reach 70°, but are mostly in the range of 5-10°. On this basis, all known asteroids of the main belt are divided approximately equally into flat (with orbital inclinations up to 8°) and spherical subsystems.

During telescopic observations of asteroids, it was found that the brightness absolute majority they change in a short time (from several hours to several days). Astronomers have long assumed that these changes in the brightness of asteroids are associated with their rotation and are determined primarily by their irregular shape. The very first photographs of asteroids obtained with the help of spacecraft confirmed this and also showed that the surfaces of these bodies are pitted with craters or funnels of various sizes. Figures 1-3 show the first satellite images of asteroids taken by various spacecraft. Obviously, such forms and surfaces of small planets were formed during their numerous collisions with other solid celestial bodies. In the general case, when the shape of an asteroid observed from the Earth is unknown (since it is visible as a point object), then they try to approximate it using a triaxial ellipsoid.

Table 1 provides basic information about the largest or simply interesting asteroids.

Table 1. Information about some asteroids.

N	Asteroid Name Rus./Lat.	Diameter (km)	Weight (10 15 kg)	Period rotation (hour)	Orbital. period (years)	Range. Class	Big p / axis orb. (a.u.)	Eccentricity orbits
1	Ceres/ Ceres	960 x 932	87000	9,1	4,6	With	2,766	0,078
2	Pallas/ Pallas	570 x 525 x 482	318000	7,8	4,6	U	2,776	0,231
3	Juno/ Juno	240	20000	7,2	4,4	S	2,669	0,258
4	Vesta/ Vesta	530	300000	5,3	3,6	U	2,361	0,090
8	Flora/ Flora	141		13,6	3,3	S		0,141
243	Ida	58 x 23	100	4,6	4,8	S	2,861	0,045
253	Matilda/ Mathilde	66 x 48 x 46	103	417,7	4,3	C	2,646	0,266
433	Eros/Eros	33 x 13 x 13	7	5,3	1,7	S	1,458	0,223
951	Gaspra/ Gaspra	19 x 12 x 11	10	7,0	3,3	S	2,209	0,174
1566	Icarus/ Icarus	1,4	0,001	2,3	1,1	U	1,078	0,827
1620	Geographer/ geographos	2,0	0,004	5,2	1,4	S	1,246	0,335
1862	Apollo/ Apollo	1,6	0,002	3,1	1,8	S	1,471	0,560
2060	Chiron/ Chiron	180	4000	5,9	50,7	B	13,633	0,380
4179	Toutatis/ Toutatis	4.6 x 2.4 x 1.9	0,05	130	1,1	S	2,512	0,634
4769	Castalia/ Castalia	1.8 x 0.8	0,0005		0,4		1,063	0,483

Explanations for the table.

1 Ceres is the largest asteroid ever discovered. It was discovered by the Italian astronomer Giuseppe Piazzi on January 1, 1801 and named after the Roman goddess of fertility.

2 Pallas is the second largest asteroid, also the second to be discovered. This was done by the German astronomer Heinrich Olbers on March 28, 1802.

3 Juno - discovered by C. 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 a basaltic crust covering the olivine mantle, which may be the result of melting and differentiation of its substance. The image of the visible disk of this asteroid was first obtained in 1995 using the American Space Telescope. Hubble in Earth orbit.

8 Flora is the largest asteroid of a large family of asteroids called by the same name, numbering several hundred members, which was first characterized by the Japanese astronomer K. Hirayama. The 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 imaged by the Galileo spacecraft on August 28, 1993. These images made it possible to detect 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 Icarus - an asteroid approaching the Earth and crossing its orbit, having a very large orbital eccentricity (0.8268).

1620 Geographer is 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 own axis, as well as from its radar images.

1862 Apollo - the largest asteroid of the same family of bodies approaching the Earth and crossing its orbit. The eccentricity of Apollo's orbit is quite large - 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 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.

4179 Toutatis is a binary asteroid whose components appear to be in contact and measure approximately 2.5 km and 1.5 km. Images of this asteroid were obtained using radars located in Arecibo and Goldstone. Of all the currently known near-Earth asteroids in the 21st century, Toutatis should be at the closest distance (about 1.5 million km, September 29, 2004).

4769 Castalia is a double asteroid with approximately identical (0.75 km in diameter) components in contact. Its radio image was obtained using radar in Arecibo.

Image of asteroid 951 Gaspra

Rice. 1. Image of asteroid 951 Gaspra, obtained with the help of the Galileo spacecraft, in pseudo-colors, that is, as a combination of images through purple, green and red filters. The resulting colors are specially boosted to highlight subtle differences in surface detail. Areas of rock outcrops have a bluish tint, while areas covered with regolith (crushed material) have a reddish tint. The spatial resolution at each point of the image is 163 m. Gaspra has an irregular shape and approximate dimensions along 3 axes of 19 x 12 x 11 km. The sun illuminates the asteroid from the right.
Image of NASA GAL-09.

Image of asteroid 243 Ides

Rice. 2 Pseudocolor image of asteroid 243 Ida and its small moon Dactyl, taken by the Galileo spacecraft. The original images used to obtain the image shown in the figure were obtained from a distance of approximately 10,500 km. Color differences may indicate variations in the composition of the surface matter. The bright blue areas are probably covered with a substance consisting of iron-bearing minerals. The length of Ida is 58 km, and its axis of rotation is oriented vertically with a slight inclination to the right.
NASA GAL-11 image.

Rice. 3. Image of Dactyl, a small satellite of 243 Ida. It is not yet known whether it is a piece of Ida, broken off from her in some kind of collision, or a foreign object captured by her. gravitational field and moving in a circular orbit. This image was taken on August 28, 1993 through a neutral density filter from a distance of about 4000 km, 4 minutes before the closest approach to the asteroid. Dactyl measures approximately 1.2 x 1.4 x 1.6 km. Image of NASA GAL-04

Asteroid 253 Matilda

Rice. 4. Asteroid 253 Matilda. NASA image, NEAR spacecraft

2. How could the main asteroid belt have arisen?

The orbits of the bodies concentrated in the main belt are stable and have a shape close to circular or slightly eccentric. Here they move in a "safe" zone, where the gravitational influence of the big planets on them, and first of all, Jupiter, is minimal. The scientific facts available today show that it was Jupiter that played the main role in the fact that another planet could not arise on the site of the main asteroid belt during the birth of the solar system. But even at the beginning of our century, many scientists were still convinced that there used to be another large planet between Jupiter and Mars, which for some reason collapsed. Olbers was the first to express such a hypothesis, immediately after his discovery of Pallas. He also came up with the name of this hypothetical planet - Phaeton. Let's make a small digression and describe one episode from the history of the solar system - the history that is based on modern scientific facts. This is necessary, in particular, to understand the origin of the main belt asteroids. Huge contribution in the formation of the modern theory of the origin of the solar system, Soviet scientists O.Yu. Schmidt and V.S. Safronov.

One of the largest bodies, formed in the orbit of Jupiter (at a distance of 5 AU from the Sun) about 4.5 billion years ago, began to increase in size faster than others. Being at the boundary of condensation of volatile compounds (H 2 , H 2 O, NH 3 , CO 2 , CH 4 , etc.), which flowed from the protoplanetary disk zone closer to the Sun and more heated, this body became the center of accumulation of matter, consisting of mainly from frozen gas condensates. Upon reaching a sufficiently large mass, it began to capture with its gravitational field the previously condensed matter located closer to the Sun, in the zone of the parent bodies of asteroids, and thus inhibit the growth of the latter. On the other hand, smaller bodies that were not captured by proto-Jupiter for any reason, but were in the sphere of its gravitational influence, were effectively scattered into different sides. Similarly, the ejection of bodies from the formation zone of Saturn probably took place, although not so intensively. These bodies also penetrated the belt of parent bodies of asteroids or planetesimals that had arisen earlier between the orbits of Mars and Jupiter, "sweeping" them out of this zone or subjecting them to crushing. Moreover, before that, the gradual growth of the parent bodies of asteroids was possible due to their low relative velocities (up to about 0.5 km/s), when the collisions of any objects ended in their unification, and not crushing. The increase in the flow of bodies thrown into the asteroid belt by Jupiter (and Saturn) during its growth led to the fact that the relative velocities of the parent bodies of the asteroids increased significantly (up to 3-5 km/s) and became more chaotic. Ultimately, the process of accumulation of parent bodies of asteroids was replaced by the process of their fragmentation during mutual collisions, and the potential for the formation of a sufficiently large planet at a given distance from the Sun disappeared forever.

3. Orbits of asteroids

returning to current state asteroid belt, it should be emphasized that Jupiter still continues to play a primary role in the evolution of asteroid orbits. The long-term gravitational influence (more than 4 billion years) of this giant planet on the asteroids of the main belt has led to the fact that there are a number of "forbidden" orbits or even zones on which there are practically no small planets, and if they get there, they cannot stay there for a long time. They are called gaps or Kirkwood hatches - after Daniel Kirkwood, the scientist who first discovered them. Such orbits are resonant, since the asteroids moving along them experience a strong gravitational effect from Jupiter. The periods of revolution corresponding to these orbits are in simple relationship with the period of circulation of Jupiter (for example, 1:2; 3:7; 2:5; 1:3, etc.). If any asteroid or its fragment, as a result of a collision with another body, falls into a resonant or close to it orbit, then the semi-major axis and eccentricity of its orbit change quite quickly under the influence of the Jupiterian gravitational field. It all ends with the asteroid either leaving its resonant orbit and may even leave the main asteroid belt, or being doomed to new collisions with neighboring bodies. In this way, the corresponding Kirkwood space is "cleared" of any objects. However, it should be emphasized that there are no gaps or empty gaps in the main asteroid belt, if we imagine the instantaneous distribution of all the bodies included in it. All asteroids, at any moment of time, fill the asteroid belt fairly evenly, since, moving along elliptical orbits, they spend most of their time in the "foreign" zone. Another, "opposite" example of the gravitational influence of Jupiter: at the outer boundary of the main asteroid belt there are two narrow additional "rings", on the contrary, made up of asteroid orbits, the periods of revolution of which are in proportions of 2:3 and 1:1 with respect to the period of revolution Jupiter. Obviously, asteroids with a period of revolution corresponding to a ratio of 1:1 are directly in the orbit of Jupiter. But they move at a distance from it equal to the radius of Jupiter's orbit, either ahead or behind. Those asteroids that are ahead of Jupiter in their movement are called "Greeks", and those that follow him are called "Trojans" (as they are named after the heroes of the Trojan War). The movement of these small planets is quite stable, since they are located at the so-called "Lagrange points", where the gravitational forces acting on them are equalized. The common name for this group of asteroids is "Trojans". Unlike Trojans, which could gradually accumulate in the vicinity of Lagrange points during the long collisional evolution of different asteroids, there are families of asteroids with very close orbits of their constituent bodies, which were most likely formed as a result of relatively recent decays of their parent bodies. This, for example, is the family of the asteroid Flora, which already has about 60 members, and a number of others. Recently, scientists have been trying to determine the total number of such families of asteroids in order to estimate the initial number of their parent bodies.

4 Near Earth Asteroids

Near the inner edge of the main asteroid belt, there are other groups of bodies whose orbits go far beyond the main belt and may even intersect with the orbits of Mars, Earth, Venus, and even Mercury. First of all, these are the groups of Amur, Apollo and Aten asteroids (according to the names of the largest representatives included in these groups). The orbits of such asteroids are no longer as stable as those of the main belt bodies, but rather rapidly evolve under the influence of the gravitational fields of not only Jupiter, but also the planets. terrestrial group. For this reason, such asteroids can move from one group to another, and the division of asteroids into the above groups is conditional, based on data on modern asteroid orbits. In particular, Amurians move in elliptical orbits, the perihelion distance (the minimum distance to the Sun) of which does not exceed 1.3 AU. The Apollos move in orbits with a perihelion distance of less than 1 AU. (recall that this is the average distance of the Earth from the Sun) and penetrate into the Earth's orbit. If for the Amurians and Apollonians the major semiaxis of the orbit exceeds 1 AU, then for the Atonians it is less than or of the order of this value, and these asteroids, therefore, move mainly inside the earth's orbit. It is obvious that the Apollos and Atons, crossing the Earth's orbit, can create a threat of collision with it. There is even a general definition of this group of small planets as "near-Earth asteroids" - these are bodies whose orbital sizes do not exceed 1.3 AU. To date, about 800 such objects have been discovered. But their total number can be much larger - up to 1500-2000 with dimensions of more than 1 km and up to 135,000 with dimensions of more than 100 m. The existing threat to the Earth from asteroids and other space bodies that are located or may end up in the Earth's environs, is widely discussed in scientific and public circles. For more on this, as well as the measures proposed to protect our planet, see a recently published book edited by A.A. Boyarchuk.

5. About other asteroid belts

There are also asteroid-like bodies beyond the orbit of Jupiter. Moreover, according to the latest data, it turned out that there are a lot of such bodies on the periphery of the solar system. This was first suggested by the American astronomer Gerard Kuiper back in 1951. He formulated the hypothesis that beyond the orbit of Neptune, at distances of about 30-50 AU. there may be a whole belt of bodies that serves as a source of short-period comets. Indeed, since the beginning of the 90s (with the introduction of the largest telescopes with a diameter of up to 10 m in the Hawaiian Islands), more than a hundred asteroid-like objects with diameters from about 100 to 800 km have been discovered beyond the orbit of Neptune. The totality of these bodies has been called the "Kuiper belt", although they are still not enough for a "full-fledged" belt. Nevertheless, according to some estimates, the number of bodies in it may be no less (if not more) than in the main asteroid belt. According to the parameters of the orbits again open bodies divided into two classes. About a third of all trans-Neptunian objects were assigned to the first, so-called "Plutino class". They move in a 3:2 resonance with Neptune along fairly elliptical orbits (major axes about 39 AU; eccentricities 0.11-0.35; orbital inclinations to the ecliptic 0-20 degrees), similar to the orbit of Pluto, from where the the name of this class. Currently, there are even discussions between scientists about whether to consider Pluto a full-fledged planet or only one of the objects of the above-named class. However, most likely, the status of Pluto will not change, since its average diameter (2390 km) is much larger than the diameters of known trans-Neptunian objects, and in addition, like most other planets in the solar system, it has a large satellite (Charon) and an atmosphere . The second class includes the so-called "typical Kuiper belt objects", since most of them (the remaining 2/3) are known and they move in orbits close to circular with semi-major axes in the range of 40-48 AU. and various slopes (0-40°). So far, the great remoteness and relatively small size prevent the discovery of new similar bodies with more rapidly, although the largest telescopes and the most modern technology are used for this. Based on the comparison of these bodies with known asteroids according to optical characteristics, it is now believed that the former are the most primitive in our planetary system. This means that since the moment of its condensation from the protoplanetary nebula, their substance has undergone very small changes in comparison, for example, with the substance of the terrestrial planets. In fact, the absolute majority of these bodies in their composition can be comet nuclei, which will also be discussed in the "Comets" section.

A number of asteroid bodies have been discovered (with time this number will probably increase) between the Kuiper belt and the main asteroid belt - this is the "class of Centaurs" - by analogy with the ancient Greek mythological centaurs (half-human, half-horse). One of their representatives is the asteroid Chiron, which would be more correctly called a comet asteroid, since it periodically exhibits cometary activity in the form of an emerging gaseous atmosphere (coma) and tail. They are formed from volatile compounds that make up the substance of this body, when it passes through the perihelion sections of the orbit. Chiron is one of good examples the absence of a sharp boundary between asteroids and comets in terms of the composition of matter and, possibly, in terms of origin. It has a size of about 200 km, and its orbit overlaps with the orbits of Saturn and Uranus. Another name for objects of this class is the Kazimirchak-Polonskaya belt, after E.I. Polonskaya, who proved the existence of asteroid bodies between the giant planets.

6. A little about the methods of researching asteroids

Our understanding of the nature of asteroids is now based on three main sources of information: ground-based telescopic observations (optical and radar), images obtained from spacecraft approaching asteroids, and laboratory analysis of known terrestrial rocks and minerals, as well as meteorites that have fallen to Earth, which ( which will be discussed in the "Meteorites" section) are mainly considered fragments of asteroids, cometary nuclei and surfaces of terrestrial planets. But we still obtain the greatest amount of information about minor planets with the help of ground-based telescopic measurements. Therefore, asteroids are divided into so-called "spectral types" or classes, in accordance, first of all, with their observed optical characteristics. First of all, this is the albedo (the proportion of light reflected by the body from the amount of sunlight falling on it per unit time, if we consider the directions of the incident and reflected rays to be the same) and the general shape of the reflection spectrum of the body in the visible and near infrared ranges (which is obtained by simply dividing on each wavelength of the spectral brightness of the surface of the observed body by the spectral brightness at the same wavelength of the Sun itself). These optical characteristics are used to assess the chemical and mineralogical composition of the matter that makes up asteroids. Sometimes additional data (if any) is taken into account, for example, on the radar reflectivity of the asteroid, on the speed of its rotation around its own axis, etc.

The desire to divide asteroids into classes is explained by the desire of scientists to simplify or schematize the description of a huge number of small planets, although, as more thorough studies show, this is not always possible. Recently, it has already become necessary to introduce subclasses and smaller divisions of the spectral types of asteroids in order to characterize some common features of their individual groups. Before giving a general description of asteroids of different spectral types, let us explain how the composition of asteroid matter can be estimated using remote measurements. As already noted, it is believed that asteroids of one type have approximately the same albedo values ​​and reflection spectra similar in shape, which can be replaced by average (for a given type) values ​​or characteristics. These average values ​​for a certain type of asteroids are compared with similar values ​​for terrestrial rocks and minerals, as well as those meteorites, samples of which are available in terrestrial collections. The chemical and mineral composition of the samples, which are called "analogue samples", together with their spectral and other physical properties, as a rule, are already well studied in terrestrial laboratories. On the basis of such a comparison and selection of analogue samples, some average chemical and mineral composition of matter for asteroids of this type is determined in the first approximation. It turned out that, unlike terrestrial rocks, the substance of asteroids as a whole is much simpler or even primitive. This suggests that the physical and chemical processes in which asteroid matter was involved throughout the entire history of the existence of the solar system were not as diverse and complex as on the terrestrial planets. If about 4000 mineral species are now considered reliably established on Earth, then on asteroids there may be only a few hundred of them. This can be judged by the number of mineral species (about 300) found in meteorites that fell to the earth's surface, which may be fragments of asteroids. A wide variety of minerals on Earth arose not only because the formation of our planet (as well as other terrestrial planets) took place in a protoplanetary cloud much closer to the Sun, and therefore at higher temperatures. In addition to the fact that the silicate substance, metals and their compounds, being in a liquid or plastic state at such temperatures, were separated or differentiated by specific gravity in the Earth's gravitational field, the prevailing temperature conditions turned out to be favorable for the emergence of a constant gaseous or liquid oxidizing medium, the main components of which were oxygen and water. Their long and constant interaction with primary minerals and rocks of the earth's crust has led to the richness of minerals that we observe. Returning to asteroids, it should be noted that, according to remote data, they mainly consist of simpler silicate compounds. First of all, these are anhydrous silicates, such as pyroxenes (their generalized formula is ABZ 2 O 6, where positions "A" and "B" are occupied by cations of different metals, and "Z" - by Al or Si), olivines (A 2+ 2 SiO 4, where A 2+ \u003d Fe, Mg, Mn, Ni) and sometimes plagioclase (with the general formula (Na,Ca)Al(Al,Si)Si 2 O 8). They are called rock-forming minerals because they form the basis of most rocks. Silicate compounds of another type, widely present on asteroids, are hydrosilicates or layered silicates. These include serpentines (with the general formula A 3 Si 2 O 5? (OH), where A \u003d Mg, Fe 2+, Ni), chlorites (A 4-6 Z 4 O 10 (OH, O) 8, where A and Z are mainly cations of different metals) and a number of other minerals that contain hydroxyl (OH) in their composition. It can be assumed that on asteroids there are not only simple oxides, compounds (for example, sulphurous) and alloys of iron and other metals (in particular FeNi), carbon (organic) compounds, but even metals and carbon in a free state. This is evidenced by the results of a study of meteorite matter, which constantly falls to the Earth (see the section "Meteorites").

7. Spectral types of asteroids

To date, the following main spectral classes or types of minor planets have been identified, denoted by Latin letters: A, B, C, F, G, D, P, E, M, Q, R, S, V, and T. Let us give a brief description of them.

Type A asteroids have a fairly high albedo and the reddest color, which is determined by a significant increase in their reflectivity towards long wavelengths. They may consist of high-temperature olivines (having a melting point in the range of 1100-1900 ° C) or a mixture of olivine with metals that correspond to the spectral characteristics of these asteroids. On the contrary, small planets of types B, C, F, and G have a low albedo (B-type bodies are somewhat lighter) and almost flat (or colorless) in the visible range, but the reflection spectrum sharply decreasing at short wavelengths. Therefore, it is believed that these asteroids are mainly composed of low-temperature hydrated silicates (which can decompose or melt at temperatures of 500-1500 ° C) with an admixture of carbon or organic compounds that have similar spectral characteristics. Asteroids with low albedo and reddish color were assigned to D- and P-types (D-bodies are redder). Such properties have silicates rich in carbon or organic matter. They consist, for example, of particles of interplanetary dust, which probably filled the near-solar protoplanetary disk even before the formation of planets. Based on this similarity, it can be assumed that D- and P-asteroids are the most ancient, little-altered bodies of the asteroid belt. Small E-type planets have the highest albedo values ​​(their surface matter can reflect up to 50% of the light falling on them) and a slightly reddish color. The mineral enstatite (this is a high-temperature variety of pyroxene) or other silicates containing iron in the free (non-oxidized) state, which, therefore, can be part of E-type asteroids, has the same spectral characteristics. Asteroids that are similar in their reflection spectra to P- and E-type bodies, but located between them in terms of albedo, are classified as M-type. It turned out that optical properties of these objects are very similar to the properties of metals in the free state or metal compounds mixed with enstatite or other pyroxenes. There are now about 30 such asteroids. With the help of ground-based observations, such an interesting fact has recently been established as the presence of hydrated silicates on a significant part of these bodies. Although the cause of such an unusual combination of high-temperature and low-temperature materials has not yet been finally established, it can be assumed that hydrosilicates could be introduced to M-type asteroids during their collisions with more primitive bodies. Of the remaining spectral classes, Q-, R-, S-, and V-type asteroids are quite similar in terms of albedo and the general shape of the reflection spectra in the visible range: they have a relatively high albedo (slightly lower for S-type bodies) and a reddish color. The differences between them boil down to the fact that the broad absorption band of about 1 micron present in their reflection spectra in the near infrared range has a different depth. This absorption band is characteristic of a mixture of pyroxenes and olivines, and the position of its center and depth depend on the proportion and total content of these minerals in the surface matter of asteroids. On the other hand, the depth of any absorption band in the reflection spectrum of a silicate substance decreases if it contains any opaque particles (for example, carbon, metals or their compounds) that screen diffusely reflected (that is, transmitted through the substance and carrying information about its composition) light. For these asteroids, the absorption band depth at 1 µm increases from S-to Q-, R-, and V-types. In accordance with the foregoing, the bodies of the listed types (except V) may consist of a mixture of olivines, pyroxenes, and metals. The substance of V-type asteroids may include, along with pyroxenes, feldspars, and be similar in composition to terrestrial basalts. And, finally, the last, T-type, includes asteroids that have a low albedo and a reddish reflectance spectrum, which is similar to the spectra of P- and D-type bodies, but occupies an intermediate position between their spectra in slope. Therefore, the mineralogical composition of T-, P-, and D-type asteroids is considered to be approximately the same and corresponding to silicates rich in carbon or organic compounds.

When studying the distribution of asteroids of different types in space, a clear relationship was found between their supposed chemical and mineral composition and the distance to the Sun. It turned out that the simpler the mineral composition of a substance (the more volatile compounds it contains) these bodies have, the farther, as a rule, they are. In general, more than 75% of all asteroids are C-type and are located mainly in the peripheral part of the asteroid belt. Approximately 17% are S-type and dominate the interior of the asteroid belt. Most of of the remaining asteroids is M-type and also moves mainly in the middle part of the asteroid ring. The distribution maxima of these three types of asteroids are within the main belt. The maximum of the total distribution of E- and R-type asteroids somewhat extends beyond the inner boundary of the belt towards the Sun. It is interesting that the total distribution of P- and D-type asteroids tends to its maximum towards the periphery of the main belt and goes not only beyond the asteroid ring, but also beyond the orbit of Jupiter. It is possible that the distribution of P- and D-asteroids of the main belt overlaps with the Kazimirchak-Polonskaya asteroid belts located between the orbits of the giant planets.

In conclusion of the review of minor planets, we briefly outline the meaning of the general hypothesis about the origin of asteroids of various classes, which is increasingly being confirmed.

8. On the origin of minor planets

At the dawn of the formation of the solar system, about 4.5 billion years ago, clumps of matter arose from the gas-dust disk surrounding the Sun due to turbulent and other non-stationary phenomena, which, during mutual inelastic collisions and gravitational interactions combined to form planetesimals. With increasing distance from the Sun, the average temperature of the gas-dust substance decreased and, accordingly, its general chemical composition changed. The annular zone of the protoplanetary disk, from which the main asteroid belt subsequently formed, turned out to be near the condensation boundary of volatile compounds, in particular, water vapor. Firstly, this circumstance led to the accelerated growth of the Jupiter embryo, which was located near the indicated boundary and became the center of accumulation of hydrogen, nitrogen, carbon and their compounds, leaving the more heated central part of the solar system. Secondly, the gas-dust substance from which the asteroids were formed turned out to be very heterogeneous in composition depending on the distance from the Sun: the relative content of the simplest silicate compounds in it sharply decreased, while the content of volatile compounds increased with distance from the Sun in the region from 2, 0 to 3.5 a.u. As already mentioned, powerful perturbations from the rapidly growing embryo of Jupiter to the asteroid belt prevented the formation of a sufficiently large proto-planetary body in it. The process of accumulation of matter there was stopped when only a few dozen planetosimals of pre-planetary size (about 500-1000 km) had time to form, which then began to break up during collisions due to a rapid increase in their relative velocities (from 0.1 to 5 km / s). However, during this period, some parent bodies of asteroids, or at least those that contained a high proportion of silicate compounds and were closer to the Sun, were already heated or even experienced gravitational differentiation. Two possible mechanisms are now being considered for heating the interiors of such proto-asteroids: as a result of the decay of radioactive isotopes, or as a result of the action of induction currents induced in the substance of these bodies by powerful streams of charged particles from the young and active Sun. The parent bodies of asteroids that have survived for some reason to this day, according to scientists, are the largest asteroids 1 Ceres and 4 Vesta, the main information about which is given in Table. 1. In the process of gravitational differentiation of proto-asteroids, which experienced sufficient heating to melt their silicate substance, metal cores and other lighter silicate shells were separated, and in some cases even a basaltic crust (for example, at 4 Vesta), as in the terrestrial planets . But still, since the material in the asteroid zone contained a significant amount of volatile compounds, its average melting point was relatively low. As shown by mathematical modeling and numerical calculations, the melting temperature of such a silicate substance could be in the range of 500-1000 ° C. So, after differentiation and cooling, the parent bodies of asteroids experienced numerous collisions not only between themselves and their fragments, but also with bodies , invading the asteroid belt from the zones of Jupiter, Saturn and the more distant periphery of the solar system. As a result of a long impact evolution, proto-asteroids were fragmented into a huge number of smaller bodies, which are now observed as asteroids. At relative velocities of about several kilometers per second, collisions of bodies consisting of several silicate shells with different mechanical strengths (the more metals are contained in a solid, the more durable it is), led to "stripping" from them and crushing to small fragments in the first place. the least durable outer silicate shells. Moreover, it is believed that asteroids of those spectral types that correspond to high-temperature silicates originate from different silicate shells of their parent bodies that have undergone melting and differentiation. In particular, M- and S-type asteroids can be entirely the cores of parent bodies (for example, S-asteroid 15 Eunomia and M-asteroid 16 Psyche with diameters of about 270 km) or their fragments due to the high content they contain metals. A- and R-type asteroids can be fragments of intermediate silicate shells, while E- and V-type asteroids can be fragments of outer shells of such parent bodies. Based on the analysis of the spatial distributions of E-, V-, R-, A-, M-, and S-type asteroids, one can also conclude that they have undergone the most intense thermal and impact reworking. This can probably be confirmed by the coincidence with the inner boundary of the main belt or the proximity to it of the distribution maxima of these types of asteroids. As for asteroids of other spectral types, they are considered either partially changed (metamorphic) due to collisions or local heating, which did not lead to their general melting (T, B, G and F), or primitive and little changed (D, P, C and Q). As already noted, the number of asteroids of these types increases towards the periphery of the main belt. There is no doubt that they all also experienced collisions and crushing, but this process was probably not so intense as to noticeably affect their observed characteristics and, accordingly, the chemical-mineral composition. (This issue will also be discussed in the "Meteorites" section). However, as shown by numerical simulation of collisions of asteroid-sized silicate bodies, many of the currently existing asteroids after mutual collisions could reaccumulate (that is, combine from the remaining fragments) and therefore are not monolithic bodies, but moving “heaps of cobblestones”. There are numerous observational confirmations (from specific brightness changes) of the presence of small satellites in a number of asteroids gravitationally bound to them, which probably also arose during impact events as fragments of colliding bodies. This fact, although it caused heated debate among scientists in the past, was convincingly confirmed by the example of the asteroid 243 Ida. With the help of the Galileo spacecraft, it was possible to obtain images of this asteroid along with its satellite (which was later named Dactyl), which are shown in Figures 2 and 3.

9. About what we don't know yet

Much remains unclear and even mysterious in the studies of asteroids. First, these are general problems related to the origin and evolution solid in the main and other asteroid belts and associated with the emergence of the entire solar system. Their decision is important not only for correct ideas about our system, but also to understand the causes and patterns of the emergence of planetary systems in the vicinity of other stars. Thanks to the capabilities of modern observational technology, it was possible to establish that a number of neighboring stars have large planets like Jupiter. Next in line is the discovery of smaller terrestrial planets in these and other stars. There are also questions that can only be answered by a detailed study of individual minor planets. In essence, each of these bodies is unique, as it has its own, sometimes specific, history. For example, asteroids that are members of some dynamical families (for example, Themis, Flora, Gilda, Eos, and others), which, as was said, common origin, may differ markedly in optical characteristics, which indicates some of their features. On the other hand, it is obvious that for a detailed study of all sufficiently large asteroids only in the main belt, a lot of time and effort will be required. And yet, probably, only by collecting and accumulating detailed and accurate information about each of the asteroids, and then with the help of its generalization, it is possible to gradually refine the understanding of the nature of these bodies and the basic laws of their evolution.

BIBLIOGRAPHY:

1. Threat from the sky: rock or accident? (Under the editorship of A.A. Boyarchuk). M: "Kosmosinform", 1999, 218 p.

2. Fleischer M. Dictionary of mineral species. M: "Mir", 1990, 204 p.