Asteroid Belt Material from Wikipedia the free encyclopedia
The asteroid belt is an area of the Solar system located between the orbits of Mars and Jupiter, which is a place of accumulation of many objects of various sizes, mostly irregular shapes, called asteroids or small planets.
This region is also often called the main asteroid belt[1] or simply the main belt[2][3], thereby emphasizing its difference from other similar areas of the cluster of minor planets, such as the Kuiper Belt beyond the orbit of Neptune, as well as clusters of objects of the scattered disk and the Oort cloud.
The expression "asteroid belt" came into use in the early 1850s.
The first use of this term is associated with the name of Alexander von Humboldt and his book "Kosmos – Entwurf einer physischen Weltbeschreibun".
The total mass of the main belt is approximately 4 % of the mass of the Moon, more than half of it is concentrated in the four largest objects: Ceres, (4) Vesta, (2) Pallas and (10) Hygeia.
Their average diameter is more than 400 km, and the largest of them, Ceres, the only dwarf planet in the main belt, has a diameter of more than 950 km and its mass is twice the total mass of Pallas and Vesta[7].
But most asteroids, of which there are several million, are much smaller, up to several tens of meters.
At the same time, asteroids are so strongly scattered in this area of outer space that not a single spacecraft flying through this area was damaged by them.
Diagram of the location of the asteroid belt in the Solar system
The reason for this composition of the asteroid belt is that it began to form directly near Jupiter, whose gravitational field constantly introduced serious disturbances into the orbits of planetesimals.
The excess of orbital energy received from Jupiter led to more severe collisions of these bodies with each other, which prevented them from sticking together into a protoplanet and its further enlargement.
As a result, most of the planetesimals were fragmented into numerous small fragments, most of which were either thrown out of the Solar System, which explains the low density of the asteroid belt, or moved into elongated orbits, along which they, falling into the inner region of the Solar System, collided with the planets of the Earth group; this phenomenon was called late heavy bombardment.
Collisions between asteroids occurred after this period, which led to the appearance of numerous asteroid families — groups of bodies with similar orbits and chemical composition, which include a significant number of asteroids existing today, as well as the formation of fine cosmic dust that forms the zodiac light.
In addition, the gravity of Jupiter also creates areas of unstable orbits, where there are practically no asteroids due to resonances with Jupiter.
An asteroid falling there will be thrown out of this orbit outside the Solar System in a relatively short time or will replenish the population of asteroids crossing the orbits of the inner planets.
Now there are practically no asteroids left in such areas, but the orbits of many small asteroids continue to change slowly under the influence of other factors.
The main distinguishing feature that characterizes individual asteroids is their spectrum, which can be used to judge the chemical composition of a given body.
In the main belt, depending on the chemical composition, there are 3 main spectral classes of asteroids: carbon (class C), silicate (class S) and metallic or iron (class M).
All these classes of asteroids, especially metal ones, are of interest from the point of view of the space industry in general and the industrial development of asteroids in particular.
Contents 1 History of asteroid Studies 1.1 The Titius Bode Rule 1.2 Discovery of Ceres 1.3 Discovery of Pallas and Other Asteroids 2 Studies 3 Origin 3.1 Formation 3.2 Evolution 4 Orbits and rotation 4.1 Influence of the Yarkovsky effect 4.2 Kirkwood Gaps 5 Asteroid Families and Groups 5.1 Families at the boundaries of the Main Belt 5.2 Young Families 6 Collisions 6.1 Dust 6.2 Meteorites 7 Physical Characteristics 7.1 Size and Mass 7.2 Composition 8 Main Belt Comets 9 The largest objects of the Asteroid Belt
10 11 12 13 14
9.1 Ceres 9.2 Vesta 9.3 Pallas 9.4 Hygeia Asteroids as sources of resources See also Notes References
The history of the study of asteroids The Titius — Bode rule A kind of prehistory of the beginning of the study of the asteroid belt can be considered the discovery of a dependence that approximately describes the distances of planets from the Sun, called the Titius — Bode rule.
The essence of the rule is that the location of the orbits of the planets of the Solar system can be approximately described by an empirical formula of the form:, where is the ordinal number of the planet (while for Mercury it should be assumed that the known planet does not correspond).
, and
none at all
It was first formulated and published by the German physicist and mathematician Johann Titius back in 1766[8][9][10], but despite the fact that, with the specified reservations, all six planets known at that time (from Mercury to Saturn) satisfied him, the rule did not attract attention for a long time.
This continued until Uranus was discovered in 1781, the large semi axis of its orbit exactly corresponded to the predicted formula.
After that, Johann Ehlert Bode suggested the possibility of the existence of a fifth planet from the Sun between the orbits of Mars and Jupiter, which, according to this rule, should have been located at a distance of 2.8 AU and has not yet been discovered[10].
The discovery of Ceres in January 1801, and at the specified distance from the Sun, led to increased confidence in the Titius — Bode rule among astronomers, which remained until the discovery of Neptune.
The Discovery of Ceres
Italian astronomer Giuseppe Piazzi, who discovered Ceres, which was initially considered a planet, then for two hundred years just a large asteroid and finally was finally determined in the status as a dwarf planet
The first search for a planet between Mars and Jupiter was started in 1787 by Baron Franz Xaver.
But after several years of unsuccessful observations, he realized that he needed the help of other astronomers, so in September 1800, he gathered a group of 24 scientists to jointly search for the planet, forming something like an informal club called the Lilienthal Society.
However, this group was best known as the "Himmelspolizei", or"heavenly police".
Its most famous members were William Herschel, Charles Messier and Heinrich Olbers[11].
They divided the zodiacal part of the sky near the ecliptic into 24 parts (according to the number of astronomers), giving each a zodiacal area with a width of 15° to search for a planet[12].
The task was to describe the coordinates of all the stars in the area of the zodiacal constellations at a certain moment.
In the following nights, the coordinates were checked and objects that moved a greater distance were highlighted.
The estimated displacement of the desired planet should have been about 30 arc seconds per hour, which is easy to notice.
Despite the efforts of the "celestial police", the planet was accidentally discovered by a man who was not a member of the club — an Italian astronomer from the University of Palermo in Sicily, Giuseppe Piazzi, who observed it on the night of January 1, 1801.
While compiling a complete catalog of stars from the constellation of Taurus, he discovered a small point of light moving against the background of stars.
Subsequent observations confirmed that it is not a star, but a new object of the Solar system.
Initially, Piazzi took it for a comet, but the absence of a coma prompted him to think that this object could be a planet[11].
It was located at a distance of 2.77 AU from the Sun, which almost exactly corresponded to the predictions of the Titius — Bode rule.
Piazzi named the planet Ceres, in honor of the Roman goddess of the harvest and the patroness of Sicily.
Soon after the discovery, the object was lost.
But thanks to the most complex calculations done in just a few hours by 24 year old Karl Gauss using a new, self discovered method (the method of least squares), he managed to indicate the place where to look for the fugitive, where she was soon discovered.
Fifteen months later, on March 28, 1802, Heinrich Olbers discovered the second large object in the same region of the Solar System, which was named Pallas.
Its semi major axis was about the same as that of Ceres, but the eccentricity and inclination, on the contrary, were very different from similar parameters of Ceres.
The most important thing is that both open bodies, unlike other planets, even in the most powerful telescopes of that time looked like points of light, that is, it was not possible to see their disks, and if it were not for their rapid movement, they would be indistinguishable from stars.
Therefore, on May 6, 1802, after studying the nature and size of these two new objects, William Herschel proposes to classify them as a separate class of objects, named by him "asteroids", from Greek.
αστεροειδής, which means "star like"[13][14][15].
The definition was deliberately chosen to be somewhat ambiguous, so that it would be "broad enough to cover all possible future discoveries".
However, despite Herschel's efforts to introduce this new term, for several decades astronomers continued to call newly discovered objects "planets" [8].
So, Ceres was called a planet until the 1860s, when it was still assigned to the class of asteroids, in which it was located until 2006, until, together with Pluto and some other trans Neptunian objects, it was transferred to the category of dwarf planets.
But as the number of discovered asteroids increased, the system of their classification and designation became more and more cumbersome, and in the early 1850s, at the suggestion of Alexander von Humboldt, they were excluded from the composition of planets and gradually began to be called asteroids more and more often.
It should be noted that the Austrian astronomer Josef Litov proposed another, much more informative designation — "zenareid".
Formed from the Greek names of Jupiter and Mars (Zeus and Ares), this name indicated the location of the asteroid belt between the orbits of these two planets.
However, this term was too late: the new bodies were already called by another word, besides the term "zenareid" was somewhat cumbersome and pretentious.
Therefore, it never entered science, only occasionally it is found in the old German astronomical literature[16].
By 1807, two more objects were discovered, named Juno and Vesta[17].
But the discoveries ended there.
The beginning of the era of the Napoleonic wars served as a kind of end of the first historical stage in the history of the search for asteroids.
There was no way to find new asteroids, and most astronomers decided that they were no longer there, and stopped research.
However, Karl Ludwig Henke persevered, resuming the search for new asteroids in 1830, and in 1845 discovered Astraea — the first new asteroid in 38 years.
And less than two years later, there was and Hebe is open.
After that, other astronomers around the world joined the search, and the discovery of new asteroids went at an accelerating pace — at least one per year.
With the improvement of telescopes, the pace of asteroid discovery constantly increased, and by the middle of 1868, their number exceeded a hundred.
When it became clear that, in addition to Ceres, there are many other smaller bodies at about the same distance from the Sun, in order to somehow explain this from the position of the Titius — Bode rule, a hypothesis was put forward about a planet that used to be in this orbit, the hypothetical planet Phaeton, which in the early stages of the formation of the Solar System collapsed so that its fragments became asteroids that formed the Asteroid Belt.
Subsequently, this hypothesis was refuted, because it turned out that due to the gravitational influence of Jupiter at a given distance from the Sun, any large body simply cannot be formed.
With the discovery of Neptune in 1846, the Titius — Bode rule turned out to be completely discredited in the eyes of scientists, since the semimajor axis of this planet was far from the predicted rule[18].
Planet
i
Mercury Venus Earth Mars Asteroid Belt Jupiter Saturn Uranus Neptune Pluto Eris
−1 0 1 2 3 4 5 6 7 8
The radius of the orbit (a. e.) according to the actual rule 0 0,4 0,39 1 0,7 0,72 2 1,0 1,00 4 1,6 1,52 8 2,8 on Wednesday.
2,2—3,6 16 5,2 5,20 32 10,0 9,54 64 19,6 19,22 drops out 30.06 128 38.8 39.5 256 77.2 67.7 k
A new stage in the study of asteroids began with the use of the astrophotography method by Max Wolf in 1891 to search for new asteroids[19].
It consisted in the fact that in photos with a long exposure period, asteroids left short light lines, while the stars remained points due to the fact that the telescope turns after the rotation of the celestial sphere.
This method significantly accelerated the detection of new asteroids compared to previously used methods of visual observation: Max Wolf alone discovered 248 asteroids, starting with the asteroid (323) Brucia, whereas a little more than 300 were discovered in a few decades before it.
The first thousand asteroids were discovered by October 1921, 10,000 by 1981[20], by 2000 the number of discovered asteroids exceeded 100,000, and as of September 6, 2011, the number of numbered asteroids is already 285,075[21].
It is known that the asteroid belt contains a much larger number of them than is known now (it all depends on how small bodies can be called asteroids).
However, since modern systems for searching for new asteroids allow them to be detected completely automatically, almost without human participation, most scientists do not search for them, calling asteroids "space debris" left after the formation of the Solar System.
Now more attention is being paid to asteroids that are potentially dangerous for the Earth.
They are called near Earth asteroids and are part of a group of near Earth objects, which also include some comets and meteoroids.
Research The first spacecraft to fly through the asteroid belt was Pioneer 10, which flew to the main belt region on July 16, 1972.
At that time, there was still concern about the possibility of a collision of the spacecraft with one of the small asteroids, but since then, 9 spacecraft have already flown through the asteroid belt on their way to the outer planets without any incidents.
The Pioneer 11, Voyager 1 and Voyager 2 spacecraft, as well as the Ulysses probe, flew through the belt without planned or accidental approaches to asteroids.
The Galileo spacecraft became the first spacecraft to take pictures of asteroids.
The first objects photographed were the asteroid (951) Gaspra in 1991 and the asteroid (243) Ida in 1993.
After that, NASA adopted a program according to which any vehicle flying through the asteroid belt should, if possible, fly past an asteroid.
In the following years, space probes and spacecraft obtained images of a number of small objects, such as (253) Matilda in 1997 from the NEAR Shoemaker spacecraft, (2685) Mazursky in 2000 from Cassini, (5535) Annafrank in 2002 from Stardust, (132524) APL in 2006 from the New Horizons probe, (2867) Steins in 2008 and (21) Lutetia in 2010 from Rosetta[22].
The flight of the Dawn spacecraft to the asteroids (4) Vesta (left) and Ceres (right)
Most of the images of asteroids of the main belt transmitted by spacecraft were obtained as a result of a brief flight of probes near asteroids on the way to the main goal of the mission — only two vehicles were sent for a detailed study of asteroids: NEAR Shoemaker, which investigated (433) Eros and Matilda[23], as well as Hayabusa, whose main goal was to study (25143) Itokawa.
The spacecraft has been studying the surface of the asteroid for a long time and even, for the first time in history, delivered soil particles from its surface[24].
for a long time, he studied the surface of an asteroid and even, for the first time in history, delivered soil particles from its surface[24].
On September 27, 2007, an automatic interplanetary station Dawn was sent to the largest asteroids Vesta and Ceres.
The spacecraft reached Vesta on July 16, 2011 and entered its orbit.
After studying the asteroid for six months, he headed for Ceres, which he reached in 2015.
If the probe continues to work after studying these two asteroids, it is possible to expand its mission to explore Pallas[25].
Space researchers make various assumptions about the reason for the large concentration of asteroids in the relatively narrow space of the interplanetary medium between the orbits of Mars and Jupiter.
The most popular among the prevailing hypotheses in the XIX century about the origin of the bodies of the asteroid belt was the hypothesis proposed in 1802, shortly after the discovery of Pallas, by the German scientist Heinrich Olbers.
He suggested that Ceres and Pallas may be fragments of the hypothetical planet Phaethon, which once existed between the orbits of Mars and Jupiter and was destroyed as a result of a collision with a comet many millions of years ago[19].
However, more recent studies refute this hypothesis.
The arguments against this are the very large amount of energy required to destroy an entire planet, the extremely small total mass of all the asteroids of the main belt, the distribution diagram of the asteroids of the main belt, which is only 4 % of the mass of the Moon, and the practical impossibility of forming a belt depending on the inclination of the orbit and a large object like a planet in the region of the Solar system experiencing strong Red — gravitational disturbances from Jupiter.
Significant differences in the chemical composition of the central regions, blue the periphery of asteroids also exclude the possibility of their origin from one body[26].
Most likely, the asteroid belt is not a destroyed planet, but a planet that could not form due to the gravitational influence of Jupiter and, to a lesser extent, other giant planets.
In general, the formation of planets and asteroids of the Solar system is close to the description of this process in the nebular hypothesis, according to which 4.5 billion years ago clouds of interstellar gas and dust under the influence of gravity formed a rotating gas dust disk, in which the disk matter was compacted and condensed.
During the first few million years of the history of the Solar System, as a result of turbulent and other non stationary phenomena, clumps of matter appeared as a result of sticking together during mutual collisions of small particles of frozen gas and dust.
This process is called accretion.
Mutual inelastic collisions, along with the gravitational interaction increasing as their size and mass increased, caused an increase in the growth rate of the clots.
Then the clumps of matter attracted the surrounding dust and gas, as well as other clumps, combining into planetesimals, from which planets were subsequently formed[27][28].
Artistic representation of a protoplanetary disk around a star
With increasing distance from the Sun, the average temperature of the gas dust substance decreased, and, accordingly, its overall chemical composition changed.
The annular zone of the protoplanetary disk, from which the main asteroid belt was subsequently formed, turned out to be near the boundary of condensation of volatile compounds, in particular, water vapor.
This is the reason for the formation of an asteroid belt in this place instead of a full fledged planet.
The proximity of this boundary led to the outstripping growth of the Jupiter embryo, which was located nearby and became the center of accumulation of hydrogen, nitrogen, carbon and their compounds, leaving the more heated central part of the Solar System.
Powerful gravitational perturbations from the rapidly growing embryo of Jupiter prevented the formation of a sufficiently large protoplanetary body in the asteroid belt[29].
The process of accumulation of matter stopped there at the moment when only a few dozen planetesimals of pre planetary size (about 500-1000 km) had time to form, which then began to break up during collisions [30], due to the rapid growth of their relative velocities (from 0.1 to 5 km/s)[31].
The reason for their growth lies in the orbital resonances, namely, in the so called Kirkwood slits, corresponding to the orbits, the periods of rotation on which correspond to the period of Jupiter's rotation as integers (4:1, 3:1, 5:2).
In such orbits, the approach is Jupiter happens most often and its gravitational influence is maximum, so there are practically no asteroids there.
Between the orbits of Mars and Jupiter there are several zones of such resonances, more or less strong.
At a certain stage of its formation, Jupiter began to migrate to the inner part of the Solar System[32], as a result, these resonances swept across the entire belt, introducing disturbances into the orbits of asteroids and increasing the speed of their movement[33].
At the same time, proto asteroids experienced numerous collisions, not only with each other, but also with bodies that invaded the asteroid belt from the zones of Jupiter, Saturn and the more distant periphery of the Solar System.
Prior to this, the gradual growth of the parent bodies of asteroids was possible due to their small relative velocities (up to 0.5 km / s), when collisions of objects ended with their unification, rather than fragmentation.
The increase in the flow of bodies thrown into the asteroid belt by Jupiter and Saturn led to the fact that the relative velocities of the parent asteroid bodies increased significantly (up to 3-5 km/s) and became more chaotic, which made the process of further enlargement of the bodies impossible.
The process of accumulation of the parent bodies of asteroids was replaced by the process of their fragmentation during mutual collisions, and the possibility of forming a large planet at a given distance from the Sun disappeared forever[34].
It is assumed that as a result of gravitational perturbations, most of the material of the main belt was dispersed during the first two million years from the moment of its formation, leaving less than 0.1 % of the substance from the initial mass, which, according to the results of computer modeling, could be enough to form a planet with the mass of the Earth[30].
It is quite possible that some of these asteroids could have survived in the Kuiper Belt or among the icy bodies of the Oort Cloud, but a significant part was probably simply thrown out of the Solar System.
Evolution
Since the formation of the primary nebula, most asteroids have undergone significant changes, which were caused by significant heating in the first few million years after their formation, the differentiation of the subsurface in large planetesimals and the fragmentation of the latter into separate smaller fragments, melting of the surface as a result of micrometeorite impacts and the influence of cosmic weathering processes that occurred under the influence of solar radiation throughout the history of the Solar System[35][36][37][38].
Despite this, many scientists continue to consider them remnants of planetesimals and hope to find in them the primary substance that made up the gas dust cloud and which could be preserved in the depths of asteroids[39], others believe that since the formation of asteroids, they have undergone too serious changes[40].
At the same time, the region of the gas dust cloud from which the asteroids were formed, due to its rather specific location, turned out to be very heterogeneous in composition, depending on the distance from the Sun: with distance from the Sun (in the region from 2.0 to 3.5 AU), the relative content of the simplest silicate compounds in it sharply decreased, and the content of light volatile compounds, in particular, water, on the contrary, increased.
At the same time, many of the parent bodies of modern asteroids were in a partially or completely melted state.
At least, those of them that contained a high proportion of silicate compounds and were closer to the Sun were already warmed up and experienced gravitational differentiation of the subsurface (stratification of matter into more and less dense), and some of them could even survive periods of active volcanism and form about
