Asteroids are relatively small celestial bodies that orbit around the sun. They are significantly inferior in size and mass to the planets, have an irregular shape and have no atmosphere.
In this section of the site, everyone can learn a lot of interesting facts about asteroids. You may already be familiar with some, others will be new to you. Asteroids are an interesting spectrum of the Cosmos, and we invite you to familiarize yourself with them in as much detail as possible.
The term "asteroid" was first coined by the famous composer Charles Burney and used by William Herschel on the basis that these objects, when viewed through a telescope, look like dots of stars, while the planets look like disks.
There is still no exact definition of the term "asteroid". Until 2006, asteroids were called minor planets.
The main parameter by which they are classified is body size. Asteroids include bodies with a diameter of more than 30 m, and bodies with a smaller size are called meteorites.
In 2006, the International Astronomical Union classified most asteroids as small bodies in our solar system.
To date, hundreds of thousands of asteroids have been identified in the solar system. As of January 11, 2015, the database contains 670474 objects, of which 422636 have orbits, they have an official number, more than 19 thousand of them had official names. According to scientists, in the solar system there can be from 1.1 to 1.9 million objects larger than 1 km. Most of the asteroids known so far are within the asteroid belt between the orbits of Jupiter and Mars.
The largest asteroid in the solar system is Ceres, which measures approximately 975x909 km, but since August 24, 2006, it has been classified as a dwarf planet. The remaining two large asteroids (4) Vesta and (2) Pallas have a diameter of about 500 km. Moreover, (4) Vesta is the only object of the asteroid belt that is visible to the naked eye. All asteroids that move in other orbits can be traced during the period of passage near our planet.
As for the total weight of all asteroids in the main belt, it is estimated at 3.0 - 3.6 1021 kg, which is approximately 4% of the weight of the moon. However, the mass of Ceres accounts for about 32% of the total mass (9.5 1020 kg), and together with three other large asteroids - (10) Hygiea, (2) Pallas, (4) Vesta - 51%, that is, most asteroids differ negligible by astronomical standards.
Exploring asteroids
After William Herschel discovered the planet Uranus in 1781, the first discoveries of asteroids began. The average heliocentric distance of asteroids corresponds to the Titius-Bode rule.
Franz Xaver created a group of twenty-four astronomers at the end of the 18th century. Beginning in 1789, this group specialized in searching for a planet that, according to the Titius-Bode rule, should be located at a distance of about 2.8 astronomical units (AU) from the Sun, namely between the orbits of Jupiter and Mars. The main task was to describe the coordinates of the stars located in the area of the zodiac constellations at a particular moment. The coordinates were checked on subsequent nights, objects moving over long distances were identified. According to their assumption, the displacement of the desired planet should be about thirty arc seconds per hour, which would be very noticeable.
The first asteroid, Ceres, was discovered by the Italian Piacio, who was not involved in this project, quite by accident, on the very first night of the century - 1801. The other three - (2) Pallas, (4) Vesta and (3) Juno - were discovered in the next few years. The most recent (in 1807) was Vesta. After another eight years of meaningless searching, many astronomers decided that there was nothing more to look for, and gave up any attempt.
But Karl Ludwig Henke showed perseverance and in 1830 he again began to search for new asteroids. After 15 years, he discovered Astrea, which was the first asteroid in 38 years. And after 2 years I discovered Hebe. After that, other astronomers joined the work, and then at least one new asteroid was discovered per year (except for 1945).
The method of astrophotography for searching for asteroids was first used by Max Wolf in 1891, according to which asteroids left light short lines in a photo with a long exposure period. This method significantly accelerated the detection of new asteroids compared to the methods of visual observation used previously. Max Wolf alone managed to find 248 asteroids, while few before him managed to find more than 300. In our time, 385,000 asteroids have an official number, and 18,000 of them also have a name.
Five years ago, two independent teams of astronomers from Brazil, Spain and the US announced that they had simultaneously detected water ice on the surface of Themis, one of the largest asteroids. Their discovery made it possible to find out the origin of water on our planet. At the beginning of its existence, it was too hot, unable to hold a large amount of water. This substance appeared later. Scientists have suggested that comets brought water to Earth, but only the isotopic compositions of water in comets and terrestrial water do not match. Therefore, it can be assumed that it hit the Earth during its collision with asteroids. At the same time, scientists discovered complex hydrocarbons on Themis, incl. molecules are the precursors of life.
Name of asteroids
Initially, the asteroids were given the names of the heroes of Greek and Roman mythology, later the discoverers could call them whatever they wanted, up to their own name. At first, asteroids were almost always given female names, while only those asteroids that had unusual orbits received male names. Over time, this rule has ceased to be respected.
It is worth noting that not every asteroid can get a name, but only one whose orbit is reliably calculated. Often there were cases when the asteroid was named many years after the discovery. Until the orbit was calculated, the asteroid was given only a temporary designation representing the date of its discovery, such as 1950 DA. The first letter means the number of the crescent in the year (in the example, as you can see, this is the second half of February), respectively, the second one indicates its serial number in the indicated crescent (as you can see, this asteroid was discovered first). The numbers, as you might guess, represent the year. Since there are 26 English letters and 24 crescents, two letters have never been used in the designation: Z and I. In the event that the number of asteroids discovered during the crescent is more than 24, scientists returned to the beginning of the alphabet, namely, writing the second letter - 2, respectively, at the next return - 3, and so on.
The name of the asteroid after receiving the name consists of a serial number (number) and the name - (8) Flora, (1) Ceres, etc.
Determining the size and shape of asteroids
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 Johann Schroeter and William Herschel in 1805. Then, in the 19th century, other astronomers measured the brightest asteroids in exactly the same way. The main disadvantage of this method is significant discrepancies in the results (for example, the maximum and minimum sizes of Ceres, which were obtained by astronomers, differed by 10 times).
Modern methods for determining the size of asteroids consist of polarimetry, thermal and transit radiometry, speckle interferometry, and the radar method.
One of the highest quality and simplest is the transit method. When an asteroid moves relative to the Earth, it can pass against the background of a separated star. This phenomenon is known as asteroid occultation of stars. By measuring the duration of the star's dimming and having data on the distance to the asteroid, one can accurately determine its size. Thanks to this method, it is possible to accurately calculate the size of large asteroids, like Pallas.
The polarimetry method itself consists in determining the size based on the brightness of the asteroid. The amount of sunlight that it reflects depends on the size of the asteroid. But in many ways, the brightness of the asteroid depends on the albedo of the asteroid, which is determined by the composition that makes up the surface of the asteroid. For example, due to its high albedo, the asteroid Vesta reflects four times as much light as Ceres and is considered the most visible asteroid, which can often be seen even with the naked eye.
However, the albedo itself is also very easy to determine. The lower the brightness of the asteroid, that is, the less it reflects solar radiation in the visible range, the more it absorbs, respectively, after it heats up, it radiates it in the form of heat in the infrared range.
It can also be used to calculate the shape of an asteroid by registering the change in its brightness during rotation, and to determine the period of this rotation, as well as to identify the largest structures on the surface. In addition, results obtained with infrared telescopes are used to determine dimensions through thermal radiometry.
Asteroids and their classification
The general classification of asteroids is based on the characteristics of their orbits, as well as a description of the visible spectrum of sunlight that is reflected by their surface.
Asteroids are usually combined into groups and families based on the characteristics of their orbits. Most often, a group of asteroids is named after the very first asteroid discovered in a given orbit. Groups are a relatively loose formation, while families are denser, formed in the past during the destruction of large asteroids as a result of collisions with other objects.
Spectral classes
Ben Zellner, David Morrison, Clark R. Champin in 1975 developed a general classification system for asteroids, which was based on albedo, color and characteristics of the spectrum of reflected sunlight. At the very beginning, this classification defined only 3 types of asteroids, namely:
Class C - carbon (most known asteroids).
Class S - silicate (about 17% of known asteroids).
Class M - metal.
This list has been expanded as more and more asteroids have been studied. The following classes have appeared:
Class A - have a high albedo and a reddish color in the visible part of the spectrum.
Class B - belong to class C asteroids, only they do not absorb waves below 0.5 microns, and their spectrum is slightly bluish. In general, the albedo is higher compared to other carbon asteroids.
Class D - have a low albedo and an even reddish spectrum.
Class E - the surface of these asteroids contains enstatite and is similar to achondrites.
Class F - similar to class B asteroids, but do not have traces of "water".
Class G - have a low albedo and an almost flat reflectance spectrum in the visible range, which indicates strong UV absorption.
Class P - just like D-class asteroids, they are distinguished by low albedo and a smooth reddish spectrum that does not have clear absorption lines.
Class Q - have wide and bright lines of pyroxene and olivine at a wavelength of 1 micron and features that indicate the presence of metal.
Class R - have a relatively high albedo and have a reddish reflection spectrum at a length of 0.7 microns.
Class T - characterized by a reddish spectrum and low albedo. The spectrum is similar to class D and P asteroids, but is intermediate in slope.
Class V - characterized by moderate bright and similar to the more common S-class, which are also more composed of silicates, stone and iron, but are distinguished by a high content of pyroxene.
Class J is a class of asteroids that were supposedly formed from the interior of Vesta. Despite the fact that their spectra are close to those of class V asteroids, at a wavelength of 1 micron they are distinguished by strong absorption lines.
It should be borne in mind that the number of known asteroids that belong to a certain type does not necessarily correspond to reality. Many types are difficult to determine, the type of an asteroid can change with more detailed studies.
Asteroid size distribution
With the growth of the size of asteroids, their number noticeably decreased. Although this generally follows a power law, there are peaks at 5 and 100 kilometers where there are more asteroids than predicted by the logarithmic distribution.
How asteroids were formed
Scientists believe that in the asteroid belt, planetesimals evolved in exactly the same way as in other areas of the solar nebula until the planet Jupiter reached its current mass, after which, as a result of orbital resonances with Jupiter, 99% of the planetesimals were ejected from the belt. Modeling and jumps in spectral properties and rotational velocity distributions show that asteroids larger than 120 kilometers in diameter were formed by accretion during this early epoch, while smaller bodies are fragments from collisions between different asteroids after or during Jupiter's gravitational dissipation of the primordial belt . Vesti and Ceres took on an overall size for gravitational differentiation, during which heavy metals sank to the core, and a crust formed from relatively rocky rocks. As for the Nice model, many Kuiper belt objects formed in the outer asteroid belt, at a distance of more than 2.6 astronomical units. And later, most of them were thrown out by the gravity of Jupiter, but those that survived may belong to class D asteroids, including Ceres.
Threat and danger from asteroids
Despite the fact that our planet is significantly larger than all asteroids, a collision with a body larger than 3 kilometers can cause the destruction of civilization. If the size is smaller, but more than 50 m in diameter, then it can lead to gigantic economic damage, including numerous victims.
The heavier and larger the asteroid, the more dangerous it is, respectively, but it is also much easier to identify it in this case. At the moment, the most dangerous asteroid is Apophis, whose diameter is about 300 meters, a collision with it can destroy an entire city. But, according to scientists, in general, it does not pose any threat to humanity when it collides with the Earth.
Asteroid 1998 QE2 approached the planet on June 1, 2013 at its closest distance (5.8 million km) in the last two hundred years.
asteroids
Asteroids. General information
Fig.1 Asteroid 951 Gaspra. Credit: NASA
In addition to the 8 large planets, the solar system includes a large number of smaller cosmic bodies similar to planets - asteroids, meteorites, meteors, Kuiper belt objects, "Centaurs". This article will focus on asteroids, which until 2006 were also called minor planets.
Asteroids are bodies of natural origin, revolving around the Sun under the influence of gravity, not related to large planets, having dimensions greater than 10 m and not showing cometary activity. Most asteroids lie in the belt between the orbits of the planets Mars and Jupiter. Within the belt, there are more than 200 asteroids whose diameter exceeds 100 km and 26 with a diameter greater than 200 km. The number of asteroids with a diameter of more than one kilometer, according to modern estimates, exceeds 750 thousand or even a million.
Currently, there are four main methods for determining the size of asteroids. The first method is based on observing asteroids through telescopes and determining the amount of sunlight reflected from their surface and the heat released. Both quantities depend on the size of the asteroid and its distance from the Sun. The second method is based on the visual observation of asteroids as they pass in front of a star. The third method involves the use of radio telescopes to obtain images of asteroids. Finally, the fourth method, which was first used in 1991 by the Galileo spacecraft, involves studying asteroids at close range.
Knowing the approximate number of asteroids within the main belt, their average size and composition, it is possible to calculate their total mass, which is 3.0-3.6 10 21 kg, which is 4% of the mass of the Moon's natural satellite of the Earth. At the same time, the 3 largest asteroids: 4 Vesta, 2 Pallas, 10 Gigei account for 1/5 of the entire mass of asteroids in the main belt. If we also take into account the mass of the dwarf planet Ceres, which was considered an asteroid until 2006, it turns out that the mass of more than a million remaining asteroids is only 1/50 of the mass of the Moon, which is extremely small by astronomical standards.
The average temperature of asteroids is -75°C.
History of observation and study of asteroids
Fig.2 The first discovered asteroid Ceres, later classified as a minor planet. Credit: NASA, ESA, J.Parker (Southwest Research Institute), P.Thomas (Cornell University), L.McFadden (University of Maryland, College Park), and M.Mutchler and Z.Levay (STScI)
The first discovered minor planet was Ceres, discovered by the Italian astronomer Giuseppe Piazzi in the Sicilian city of Palermo (1801). At first, Giuseppe thought that the object he saw was a comet, but after the German mathematician Carl Friedrich Gauss determined the parameters of the orbit of a cosmic body, it becomes clear that it is most likely a planet. A year later, according to the ephemeris of Gauss, Ceres is found by the German astronomer G. Olbers. The body, named Piazzi Ceres, in honor of the ancient Roman goddess of fertility, was at that distance from the Sun, at which, according to the Titius-Bode rule, a large planet in the solar system should have been located, which astronomers have been looking for since the end of the 18th century.
In 1802, the English astronomer W. Herschel introduces a new term "asteroid". Herschel called asteroids space objects, which, when observed through a telescope, looked like dim stars, in contrast to the planets, which, when visually observed, were disk-shaped.
In 1802-07. The asteroids Pallas, Juno and Vesta were discovered. Then came an era of calm lasting about 40 years, during which not a single asteroid was discovered.
In 1845, German amateur astronomer Karl Ludwig Henke, after 15 years of searching, discovers the fifth asteroid of the main belt - Astrea. Since that time, just a global "hunt" for asteroids of all astronomers in the world begins, because. before the discovery of Hencke in the scientific world, it was believed that there were only four asteroids and eight years of fruitless searches during 1807-15. would seem to support this hypothesis.
In 1847, the English astronomer John Hynd discovered the asteroid Iridu, after which at least one asteroid has been discovered every year until now (except 1945).
In 1891, the German astronomer Maximilian Wolf began to use the method of astrophotography to detect asteroids, in which asteroids left short light lines in photographs with a long exposure period (photolayer illumination). Using this method, Wolf was able to detect 248 asteroids in a short period of time, i.e. only slightly less than what was discovered in fifty years of observations before it.
In 1898, Eros was discovered, approaching the Earth at a dangerous distance. Subsequently, other asteroids approaching the earth's orbit were also discovered, and they were identified as a separate class of Cupids.
In 1906, Achilles was discovered sharing an orbit with Jupiter and following in front of it at the same speed. All newly discovered similar objects began to be called Trojans in honor of the heroes of the Trojan War.
In 1932, Apollo was discovered - the first representative of the Apollo class, which at perihelion approach the Sun closer than the Earth. In 1976, Aton was discovered, which marked the beginning of a new class - atons, the magnitude of the major axis of the orbit of which is less than 1 AU. And in 1977, the first minor planet was discovered that never approaches the orbit of Jupiter. Such minor planets were called Centaurs as a sign of their proximity to Saturn.
In 1976, the first near-Earth asteroid of the Atons group was discovered.
In 1991, Damocles was found, which has a very elongated and strongly inclined orbit, characteristic of comets, but does not form a cometary tail when approaching the Sun. Such objects became known as Damocloids.
In 1992, it was possible to see the first object from the belt of minor planets predicted by Gerard Kuiper in 1951. It was named 1992 QB1. After that, in the Kuiper belt every year began to find more and more large objects.
In 1996, a new era in the study of asteroids began: the US National Aeronautics and Space Administration sent the NEAR spacecraft spacecraft to the asteroid Eros, which was supposed to not only photograph the asteroid flying past it, but also become an artificial satellite of Eros, and subsequently land on its surface.
On June 27, 1997, on the way to Eros, NEAR flew at a distance of 1212 km. from the small asteroid Matilda, making over 50m black and white and 7 color images covering 60% of the asteroid's surface. The magnetic field and the mass of Matilda were also measured.
At the end of 1998, due to the loss of communication with the spacecraft for 27 hours, the time to enter the Eros orbit was postponed from January 10, 1999 to February 14, 2000. At the appointed time, NEAR entered a high asteroid orbit with a periapsis of 327 km and an apoapsis of 450 km. A gradual decrease in orbit begins: on March 10, the device entered a circular orbit with a height of 200 km, on April 11 the orbit decreased to 100 km, on December 27 there was a decrease to 35 km, after which the mission of the device entered the final stage with the aim of landing on the surface of the asteroid. At the stage of decline - March 14, 2000 "NEAR spacecraft" was renamed in honor of the American geologist and planetary scientist Eugene Shoemaker, who tragically died in a car accident in Australia, in "NEAR Shoemaker".
On February 12, 2001, NEAR began deceleration, which lasted 2 days, culminating in a soft landing on an asteroid, followed by photographing the surface and measuring the composition of the surface soil. On February 28, the mission of the apparatus was completed.
In July 1999, the Deep Space 1 spacecraft from a distance of 26 km. explored the asteroid Braille, collecting a large amount of data on the composition of the asteroid and obtaining valuable images.
In 2000, the Cassini-Huygens apparatus photographed the asteroid 2685 Masursky.
In 2001, the first Aton was discovered that did not cross the earth's orbit, as well as the first Neptune Trojan.
On November 2, 2002, NASA's Stardust spacecraft photographed the small asteroid Annafranc.
On May 9, 2003, the Japan Aerospace Exploration Agency launched the Hayabusa spacecraft to study the Itokawa asteroid and deliver asteroid soil samples to Earth.
On September 12, 2005, Hayabusa approached the asteroid at a distance of 30 km and began research.
In November of the same year, the device made three landings on the surface of an asteroid, as a result of which the Minerva robot was lost, designed to photograph individual dust particles and shoot close panoramas of the surface.
On November 26, another attempt was made to lower the apparatus in order to collect soil. Shortly before landing, communication with the device was lost and restored only after 4 months. Whether it was possible to make a soil sampling remained unknown. In June 2006, JAXA reported that Hayabusa would most likely return to Earth, which happened on June 13, 2010, when a descent capsule with asteroid particle samples was dropped near the Woomera test site in southern Australia. After examining soil samples, Japanese scientists found that Mg, Si and Al are present in the composition of the Itokawa asteroid. On the surface of the asteroid, there is a significant amount of pyroxene and olivine minerals in a ratio of 30:70. Those. Itokawa is a fragment of a larger chondrite asteroid.
After the Hayabusa apparatus, photographing of asteroids was also carried out by the New Horizons AMS (June 11, 2006 - asteroid 132524 APL) and the Rosetta spacecraft (September 5, 2008 - photographing asteroid 2867 Steins, July 10, 2010 - Lutetia asteroid). In addition, on September 27, 2007, the Dawn automatic interplanetary station was launched from the cosmodrome at Cape Canaveral, which already this year (presumably on July 16) will enter a circular orbit around the asteroid Vesta. In 2015, the device will reach Ceres - the largest object in the main asteroid belt - after working in orbit for 5 months, it will complete its work ...
Asteroids differ in size, structure, shape of orbits and location in the solar system. Based on the characteristics of their orbits, asteroids are classified into separate groups and families. The first ones are formed by fragments of larger asteroids, and therefore, the semi-major axis, eccentricity and orbital inclination of asteroids within the same group almost completely coincide. The second ones combine asteroids with similar orbital parameters.
Currently, more than 30 families of asteroids are known. Most families of asteroids are located in the main belt. Between the main concentrations of asteroids in the main belt, there are empty areas known as gaps or Kirkwood hatches. Such regions arise as a result of the gravitational interaction of Jupiter, due to which the orbits of asteroids become unstable.
There are fewer groups of asteroids than families. In the description below, the asteroid groups are listed in order of their distance from the Sun.
fig.3 Groups of asteroids: white - asteroids of the main belt; green beyond the outer boundary of the main belt - the Trojans of Jupiter; orange - Hilda's group. . Source: wikipedia
Closest to the Sun is the hypothetical belt of Vulcanoids - minor planets whose orbits lie completely inside the orbit of Mercury. Computer calculations show that the region lying between the Sun and Mercury is gravitationally stable and, most likely, small celestial bodies exist there. Their practical detection is hampered by their proximity to the Sun, and so far not a single Vulcanoid has been discovered. Indirectly, craters on the surface of Mercury speak in favor of the existence of vulcanoids.
The next group is Atons, minor planets named after the first representative, discovered by the American astronomer Eleanor Helin in 1976. Atons, the major semiaxis of the orbit is less than astronomical unit. Thus, for most of their orbital journey, the Atons are closer to the Sun than the Earth, and some of them never cross Earth's orbit at all.
More than 500 Atons are known, of which only 9 have their own names. Atons are the smallest of all groups of asteroids: the diameter of most of them does not exceed 1 km. The largest aton is Kruitna, with a diameter of 5 km.
Between the orbits of Venus and Jupiter, groups of small asteroids Amurs and Apollos stand out.
Cupids are asteroids lying between the orbits of the Earth and Jupiter. Cupids can be divided into 4 subgroups, differing in the parameters of their orbits:
The first subgroup includes asteroids lying between the orbits of the Earth and Mars. These include less than 1/5 of all cupids.
The second subgroup includes asteroids whose orbits lie between the orbit of Mars and the main asteroid belt. The long-standing name of the entire group, the asteroid Amur, also belongs to them.
The third subgroup of cupids includes asteroids whose orbits lie within the main belt. It includes about half of all cupids.
The last subgroup includes a few asteroids that lie outside the main belt and penetrate beyond the orbit of Jupiter.
To date, more than 600 cupids are known. They rotate in orbits with a semi-major axis of more than 1.0 AU. and distances at perihelion from 1.017 to 1.3 AU. e. The diameter of the largest cupid - Ganymede - 32 km.
Apollos include asteroids crossing the Earth's orbit and having a semi-major axis of at least 1 AU. Apollos, along with atons, are the smallest asteroids. Their largest representative is Sisyphus with a diameter of 8.2 km. In total, more than 3.5 thousand Apollos are known.
The above groups of asteroids form the so-called "main" belt, in which it is concentrated.
Behind the "main" asteroid belt is a class of minor planets called Trojans or Trojan asteroids.
Trojan asteroids are located in the vicinity of the Lagrange points L4 and L5 in the 1:1 orbital resonance of any planets. Most Trojan asteroids have been found near the planet Jupiter. There are Trojans near Neptune and Mars. Assume their existence near the Earth.
Jupiter's Trojans are divided into 2 large groups: at point L4 there are asteroids, called the names of Greek heroes, and moving ahead of the planet; at point L5 - asteroids, called the names of the defenders of Troy and moving behind Jupiter.
At the moment, only 7 Trojans are known from Neptune, 6 of which move ahead of the planet.
Only 4 Trojans have been found near Mars, 3 of which lie near the L4 point.
Trojans are large asteroids, often over 10 km in diameter. The largest of them is the Greek of Jupiter - Hector, with a diameter of 370 km.
Between the orbits of Jupiter and Neptune, there is a belt of Centaurs - asteroids that simultaneously exhibit the properties of both asteroids and comets. So, the first of the discovered Centaurs - Chiron, when approaching the Sun, a coma was observed.
It is currently believed that there are more than 40 thousand centaurs with a diameter of more than 1 km in the solar system. The largest of them is Chariklo with a diameter of about 260 km.
The group of damocloids includes asteroids with very elongated orbits, and located at aphelion further than Uranus, and at perihelion closer than Jupiter, and sometimes even Mars. It is believed that damocloids are the cores of the planets that have lost volatile substances, which was done on the basis of observations that showed the presence of a coma in a number of asteroids of this group and on the basis of a study of the parameters of the orbits of damocloids, as a result of which it turned out that they revolve around the Sun in the direction opposite to the movement major planets and other groups of asteroids.
Spectral classes of asteroids
By color, albedo, and spectrum characteristics, asteroids are conventionally divided into several classes. Initially, according to the classification of Clark R. Chapman, David Morrison and Ben Zellner, there were only 3 spectral classes of asteroids. Then, as scientists studied, the number of classes expanded and at the moment there are 14 of them.
Class A includes only 17 asteroids that lie within the main belt and are characterized by the presence of olivine in the composition of the mineral. Class A asteroids characterized by moderately high albedo and reddish color.
Class B includes carbonaceous asteroids with a bluish spectrum and almost no absorption at wavelengths below 0.5 µm. Asteroids of this class lie mainly within the main belt.
Class C is formed by carbon asteroids, whose composition is close to the composition of the protoplanetary cloud from which the solar system was formed. This is the most numerous class, to which 75% of all asteroids belong. They circulate in the outer regions of the main belt.
Asteroids with a very low albedo (0.02-0.05) and an even reddish spectrum without clear absorption lines belong to the spectral class D. They lie in the outer regions of the main belt at a distance of at least 3 AU. from the sun.
Class E asteroids are most likely the remnants of the outer shell of a larger asteroid and are characterized by a very high albedo (0.3 and higher). In their composition, asteroids of this class are similar to meteorites known as enstatite achondrites.
Class F asteroids belong to the group of carbon asteroids and differ from similar class B objects in the absence of traces of water, which absorbs at a wavelength of about 3 microns
Class G combines carbonaceous asteroids with strong ultraviolet absorption at a wavelength of 0.5 µm.
The class M includes metallic asteroids with a moderately large albedo (0.1-0.2). On the surface of some of them there are outcrops of metals (nickel iron), as in some meteorites. Less than 8% of all known asteroids belong to this class.
Asteroids with a low albedo (0.02-0.07) and an even reddish spectrum without specific absorption lines belong to the P class. They contain carbons and silicates. Similar objects dominate in the outer regions of the main belt.
The Q class includes a few asteroids from the inner regions of the main belt, similar in spectrum to chondrites.
Class R combines objects with a high concentration in the outer regions of olivine and pyroxene, possibly with an addition of plagioclase. There are few asteroids of this class and they all lie in the inner regions of the main belt.
Class S includes 17% of all asteroids. Asteroids of this class have a silicic or stony composition and are located mainly in regions of the main asteroid belt at a distance of up to 3 AU.
To the class of asteroids T, scientists include objects with a very low albedo, a dark surface and moderate absorption at a wavelength of 0.85 microns. Their composition is unknown.
The last class of asteroids identified to date - V, includes objects whose orbits are close to the parameters of the orbit of the largest representative of the class - the asteroid (4) Vesta. In their composition, they are close to S-class asteroids; consist of silicates, stones and iron. Their main difference from class S asteroids is their high content of pyroxene.
Origin of asteroids
There are two hypotheses for the formation of asteroids. According to the first hypothesis, the existence of the planet Phaethon in the past is assumed. It did not exist for long and collapsed in a collision with a large celestial body or due to processes inside the planet. However, the formation of asteroids is most likely due to the destruction of several large objects left after the formation of the planets. The formation of a large celestial body - a planet - within the main belt could not occur due to the gravitational influence of Jupiter.
Asteroid satellites
In 1993, the Galileo spacecraft took a picture of the asteroid Ida with a small satellite Dactyl. Subsequently, satellites were discovered around many asteroids, and in 2001 the first satellite was discovered around a Kuiper belt object.
To the bewilderment of astronomers, joint observations using ground-based instruments and the Hubble telescope have shown that in many cases these satellites are quite comparable in size to the central object.
Dr. Stern has done research to find out how such binary systems can form. The standard model for the formation of large satellites assumes that they are formed as a result of a collision of a parent object with a large object. Such a model makes it possible to satisfactorily explain the formation of binary asteroids, the Pluto-Charon system, and can also be directly applied to explain the process of formation of the Earth-Moon system.
Stern's research called into question a number of provisions of this theory. In particular, the formation of objects requires collisions with energy, which are very unlikely given the possible number and mass of Kuiper belt objects both in its original state and in the modern one.
Two possible explanations follow from this - either the formation of binary objects did not occur as a result of collisions, or the reflection coefficient of the surface of Kuiper objects (which determines their size) is significantly underestimated.
To resolve the dilemma, according to Stern, NASA's new space infrared telescope SIRTF (Space Infrared Telescope Facility), which was launched in 2003, will help.
Asteroids. Collisions with the Earth and other space bodies
From time to time, asteroids can collide with space bodies: planets, the Sun, other asteroids. They also collide with the Earth.
To date, more than 170 large craters are known on the Earth's surface - astroblems ("star wounds"), which are the places where celestial bodies fall. The largest crater for which an extraterrestrial origin has been established with a high probability is Vredefort in South Africa, with a diameter of up to 300 km. The crater was formed as a result of the fall of an asteroid with a diameter of about 10 km more than 2 billion years ago.
The second largest impact crater is Sudbury in the Canadian province of Ontario, formed by a comet fall 1850 million years ago. Its diameter is 250 km.
On Earth, there are 3 more meteorite impact craters with a diameter of more than 100 km: Chicxulub in Mexico, Manicouagan in Canada and Popigai (Popigai Basin) in Russia. The Chicxulub crater is associated with the fall of an asteroid that caused the Cretaceous-Paleogene extinction event 65 million years ago.
Currently, scientists believe that celestial bodies, equal in size to the Chicxulub asteroid, fall to Earth about once every 100 million years. Smaller bodies fall to Earth much more frequently. So, 50 thousand years ago, i.e. already at the time when people of the modern type lived on Earth, a small asteroid with a diameter of about 50 meters fell in the state of Arizona (USA). The impact created Barringer Crater, 1.2 km across and 175 m deep. In 1908, in the area of the Podkamennaya Tunguska River at an altitude of 7 km. a fireball with a diameter of several tens of meters exploded. There is still no consensus on the nature of the fireball: some scientists believe that a small asteroid exploded over the taiga, while another part believes that the nucleus of a comet was the cause of the explosion.
On August 10, 1972, a huge fireball was observed over the territory of Canada by eyewitnesses. Apparently we are talking about an asteroid with a diameter of 25 m.
On March 23, 1989, an asteroid 1989 FC with a diameter of about 800 meters flew by at a distance of 700 thousand km from the Earth. The most interesting thing is that the asteroid was discovered only after its removal from the Earth.
On October 1, 1990, a fireball with a diameter of 20 meters exploded over the Pacific Ocean. The explosion was accompanied by a very bright flash, which was recorded by two geostationary satellites.
On the night of December 8-9, 1992, many astronomers observed the passage of the asteroid 4179 Toutatis with a diameter of about 3 km past the Earth. An asteroid passes by the Earth every 4 years, so you also have the opportunity to explore it.
In 1996, a half-kilometer asteroid passed at a distance of 200 thousand km from our planet.
As you can see from this far from complete list, asteroids are quite frequent guests on Earth. According to some estimates, asteroids with a diameter of more than 10 meters invade the Earth's atmosphere every year.
> Asteroids
Everything about asteroids for children: description and explanation with photos, interesting facts about an asteroid and meteorites, asteroid belt, fall to Earth, types and name.
For the little ones it is important to remember that an asteroid is a small rocky object, devoid of air, orbiting a star, and not large enough to qualify as a planet. Parents or teachers at school may explain to children that the total mass of asteroids is inferior to that of the earth. But do not think that their size is not a threat. In the past, many of them crashed into our planet, and this may happen again. That is why researchers are constantly studying these objects, calculating the composition and trajectory. And if a dangerous space stone is rushing at us, then it’s better to prepare.
Formation of asteroids - explanation for children
To begin explanation for children It is possible from the fact that asteroids are the residual material after the formation of our system 4.6 billion years ago. When it was formed, it simply did not allow other planets to appear in the gap between itself and. Because of this, small objects collided there and turned into asteroids.
It is important to children understood this process, because every day scientists are plunging deeper into the past. Two theories have been circulating lately: the Nice model and the Grand Tack. They believe that before settling into their usual orbits, the gas giants traveled through the system. This movement could have pulled asteroids out of the main belt, changing its original appearance.
Physical characteristics of asteroids - explanation for children
Asteroids vary in size. Some may be as large as Ceres (940 km wide). If we take the smallest, then it was 2015 TC25 (2 meters), flying close to us in October 2015. But children may not worry, since in the near future there is little chance for asteroids to head towards us.
Almost all asteroids formed in an irregular shape. Although the largest ones can approach the sphere. They show depressions and craters. For example, Vesta has a huge crater (460 km). The surface of most is littered with dust.
Asteroids also go around the star in an ellipse, so they make chaotic somersaults and turns on their way. For the little ones it will be interesting to hear that some have a small satellite or two moons. There are binary or double asteroids, as well as triple ones. They are about the same size. Asteroids can evolve if they are grabbed by the planet's gravity. Then they increase their mass, go into orbit and turn into satellites. Among the candidates: and (Martian satellites), as well as most of the satellites near Jupiter, and.
They differ not only in size, but also in shape. They are solid pieces or small fragments bound together by gravity. Between Uranus and Neptune there is an asteroid with its own ring system. And one more is endowed with six tails!
The average temperature reaches -73°C. For billions of years, they have existed almost unchanged, so it is important to explore them in order to take a look at the primitive world.
Classification of asteroids - explanation for children
The objects are located in three zones of our system. Most of it is clustered in a giant annular region between the orbits of Mars and Jupiter. This is the main belt, with more than 200 asteroids with a diameter of 100 km, as well as from 1.1-1.9 million with a diameter of 1 km.
Parents or at school must explain to children that not only the asteroids of the solar system live in the belt. Previously, Ceres was considered an asteroid until it was transferred to the class of dwarf planets. Moreover, not so long ago, scientists have identified a new class - "main belt asteroids." These are small stone objects with tails. The tail appears when they crash, break up, or in front of you is a hidden comet.
A lot of stones are located outside the main belt. They gather near the major planets in certain places (Lagrange point) where the solar and planetary gravity are in balance. Most representatives are the Trojans of Jupiter (in terms of numbers, they almost reach the number of the asteroid belt). They also have Neptune, Mars and Earth.
Near-Earth asteroids orbit closer to us than . Cupids come close in orbit, but do not intersect with the earth. The Apollos intersect with our orbit, but most of the time they are located in the distance. Atons also cross the orbit, but are inside it. Atyrs are the closest. According to the European Space Agency, we are surrounded by 10,000 known near-Earth objects.
In addition to the division into orbits, they also come in three classes in composition. C-type (carbonaceous) is gray and occupies 75% of known asteroids. Most likely, they are formed from clay and stony silicate rocks and inhabit the outer zones of the main belt. S-type (silica) - green and red, represent 17% of the objects. Created from silicate materials and nickel-iron and dominate the inner belt. M-type (metal) - red and make up the rest of the representatives. Consists of nickel-iron. Of course, children should be aware that there are many more varieties based on composition (V-type - Vesta, which has a basalt volcanic crust).
Asteroid attack - explanation for children
4.5 billion years have passed since the formation of our planet, and the fall of asteroids to Earth was a frequent occurrence. To cause serious damage to the Earth, an asteroid would have to be ¼ mile wide. Because of this, such an amount of dust will rise into the atmosphere that will form the conditions of a “nuclear winter”. On average, strong impacts occur once every 1000 years.
Smaller objects fall at intervals of 1000-10000 years and can destroy an entire city or create a tsunami. If the asteroid does not reach 25 meters, it will most likely burn up in the atmosphere.
Dozens of potential dangerous strikers travel in outer space, who are constantly monitored. Some are pretty close, while others are considering doing so in the future. To have time to react, there should be a margin of 30-40 years. Although now more and more people are talking about the technology of dealing with such objects. But there is a danger of missing the threat and then there simply will not be time to react.
Important explain to the little ones that a possible threat is fraught with benefits. After all, once it was an asteroid impact that caused our appearance. When formed, the planet was dry and barren. Falling comets and asteroids left water and other carbon-based molecules on it, which allowed life to form. During the formation of the solar system, objects stabilized and allowed modern life forms to gain a foothold.
If an asteroid or part of it falls on a planet, then it is called a meteorite.
Composition of asteroids - explanation for children
- Iron meteorites: iron (91%), nickel (8.5% ), cobalt (0.6%).
- Stony meteorites: oxygen (6%), iron (26%), silicon (18%), magnesium (14%), aluminum (1.5%), nickel (1.4%), calcium (1.3%) .
Discovery and name of asteroids - explanation for children
In 1801, an Italian priest, Giuseppe Piazzi, was creating a star map. Quite by chance, between Mars and Jupiter, he noticed the first and large asteroid Ceres. Although today it is already a dwarf planet, because its mass accounts for ¼ of the mass of all known asteroids in the main belt or nearby.
In the first half of the 19th century, a lot of such objects were found, but they were all classified as planets. It wasn't until 1802 that William Herschel proposed the word "asteroid", although others continued to refer to them as "minor planets". By 1851, 15 new asteroids had been found, so the naming principle had to be changed by adding numbers. For example, Ceres became (1) Ceres.
The International Astronomical Union is not strict about naming asteroids, so now you can find objects named after Star Trek's Spock or rock musician Frank Happa. 7 asteroids are named after the crew of the Columbia spacecraft who died in 2003.
Also, numbers are added to them - 99942 Apophis.
Asteroid exploration - explanation for children
The Galileo spacecraft took close-up shots of asteroids for the first time in 1991. In 1994, he also managed to find a satellite orbiting an asteroid. NASA has been studying the Eros near-Earth object for a long time. After much deliberation, they decided to send a device to him. NEAR made a successful landing, becoming the first in this regard.
Hayabusa was the first spacecraft to land and take off from an asteroid. He set off in 2006 and returned in June 2010, bringing samples with him. NASA launched the Dawn mission in 2007 to study Vesta in 2011. A year later, they left the asteroid for Ceres and reached it in 2015. In September 2016, NASA sent OSIRIS-REx to explore the asteroid Bennu.
What are asteroids?
An asteroid is a large piece of rock, ice, or metal found in outer space. Asteroids are very different. Some may be the size of an entire city, but there are also tiny asteroids the size of an ordinary grain of sand or a small pebble from a sandbox. Due to their relatively small size, asteroids cannot turn into more or less regular spheres, as happened with planets, so the shape of asteroids is often elongated, with bumps and depressions on the surface. Astronomers are most comfortable classifying asteroids by their location in space and their ability to reflect light. This is quite simple, because the asteroids themselves do not glow like stars, but can only reflect the light of the Sun, like the rest of the planets in our solar system. And the better an asteroid reflects light, the easier it is to see from Earth, which is why astronomers like to separate chunks of ice and rock in space into groups of brighter and dimmer asteroids.
Where are the asteroids located?
There are a lot of asteroids in our solar system. They revolve around the sun , like the rest of the planets, only their orbits can be more elongated and more different from circular ones. Asteroids can also move around planets. For example , Saturn's famous rings are made up of asteroids orbiting this planet much like the moon orbits the earth. In addition, there are several places of large accumulation of asteroids in the solar system. These places are called asteroid belts. One of them - main belt - located between Mars and Jupiter, the second - beyond the orbit of Neptune. Asteroids in the main belt vary in composition. Those closer to the Sun are mostly made up of metals, while those farther away , made of stone. The asteroid belt beyond the orbit of Neptune is called the Kuiper belt. Since the asteroids in this belt are very far from the Earth, scientists still know little about them. We only know that they are made of frozen gases and water.
Where did the main asteroid belt come from?
Asteroids are the material from which the planets of the solar system were created. Astronomers believe that there was enough of this material in the space between Mars and Jupiter to form another small planet, but the strong gravitational field of neighboring planets prevented the asteroids from coalescing together. Some scientists suggest that there was once a very small planet in the place of the asteroid belt, but it was destroyed due to collisions with other asteroids or was torn apart by the attraction of the Sun on one side and Jupiter on the other.
Are there many large asteroids?
There are only 26 large asteroids. And the largest are Ceres, which recently received the title of a dwarf planet for its size, then Pallas and Vesta. Their dimensions are such that if there was a metro on Pallas, then from one end of the asteroid to the other one would have to travel all night without stopping.
What will happen, if you add all the asteroids together?
Despite the presence of very large asteroids, the total mass of all asteroids in the solar system is only 4% of the mass of the moon. Therefore, if we replace our Moon with asteroids stuck together, then in the sky instead of the Moon we will see only a small, very bright star.
Comparative sizes of the asteroid Vesta, the dwarf planet Ceres and the Moon.
Some asteroids
Ida and Dactyl
The asteroid Ida is located in the main asteroid belt between Mars and Saturn. This small asteroid size "only » The city of St. Petersburg is interesting because it has its own satellite - Daktil.
Vesta
Before Ceres was recognized as a dwarf planet, Vesta was considered the third asteroid in size after her and Pallas, and was the second in mass, second only to Ceres. It is also the brightest asteroid of all, and the only one that can be effortlessly observed with the naked eye.
Cleopatra
Cleopatra is a relatively large dumbbell-shaped asteroid. It is believed that earlier these were two different asteroids that once collided, stuck together, and remained flying, connected forever.
In February 2011, a joke appeared in the Russian-language media, citing some "Brazilian astronomers", that Cleopatra had changed her orbit and was moving towards the Earth. The source and purpose of this invention is unknown.
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