Survey of bodies of the solar system. Asteroids and dwarf planets

asteroid orbits

Asteroids of the Main Belt move in stable orbits, close to circular or slightly eccentric. They are in the "safe" zone, where the gravitational influence of the large planets on them is minimal, in the first place, Jupiter. It is believed that it is Jupiter that is “to blame” for the fact that a large planet could not form on the site of the Main Asteroid Belt during the youth of the solar system.

However, at the beginning of the 20th century many scientists believed that between Jupiter and Mars there used to be a large planet, which for some reason collapsed. Olbers was the first to express this hypothesis, immediately after his discovery of Pallas. He also suggested calling the hypothetical planet Phaeton. However, modern cosmogony has abandoned the idea of ​​the destruction of a large planet: the asteroid belt probably always contained many small bodies, which were prevented from uniting by the influence of Jupiter.

This giant still continues to play a primary role in the evolution of asteroid orbits. Its long-term (more than 4 billion years) gravitational influence on the asteroids of the Main Belt led to the emergence of a number of "forbidden" orbits and even zones in which there are practically no small bodies, and if they get there, they cannot stay there for a long time . These zones are called Kirkwood gaps (or hatches) after Daniel Kirkwood (1814-1895), who first discovered them in the distribution of the orbital periods of just a few dozen asteroids.

Orbits in Kirkwood hatches are called resonant, since the asteroids moving along them experience regular gravitational perturbation from Jupiter at the same points of their orbit. The periods of revolution in these orbits are in simple ratio with the period of revolution of Jupiter (for example, 1:2, 3:7, 2:5, 1:3). If any asteroid, for example, as a result of a collision with another body, falls into a resonant orbit, then its eccentricity and semi-major axis rapidly change under the influence of Jupiter's gravitational field. The asteroid is leaving its resonant orbit and may even leave the Main Belt. This is Kirkwood's permanent "clean-up" mechanism.

However, we note that if we depict the instantaneous distribution of all the asteroids of the Main Belt, then we will not see any “gaps”. At any given time, the asteroids fill the belt quite evenly, because, moving in elliptical orbits, they often cross the “forbidden zones”.

There is another, opposite, example of the gravitational influence of Jupiter: at the outer boundary of the Main Asteroid Belt there are two narrow "zones" containing an excess number of asteroids. The periods of revolution in them are in proportions of 2:3 and 1:1 with the period of revolution of Jupiter. It is clear that the 1:1 resonance means that the asteroids are moving almost in the orbit of Jupiter. But they do not approach the giant planet, but keep a distance, on average, equal to the radius of Jupiter's orbit. These asteroids were named after the heroes of the Trojan War. Those of them that are ahead of Jupiter in their orbit are called "Greeks", and the lagging group is called "Trojans" (both groups together are often called "Trojans"). The movement of these small bodies takes place in the vicinity of the “triangular Lagrange points”, where gravitational and centrifugal forces are equalized during circular motion. It is important that with a small deviation from the equilibrium position, forces arise that tend to return the object to its place, i.e. its movement is steady.

An asteroid is a relatively small, rocky cosmic body, similar to a planet in the solar system. Many asteroids revolve around the Sun, and their largest cluster is located between the orbits of Mars and Jupiter and is called the asteroid belt. Here, is the largest of the known asteroids - Ceres. Its dimensions are 970x940 km, i.e., almost rounded. But there are those whose sizes are comparable to dust particles. Asteroids, like comets, are the remains of the substance from which our solar system was formed billions of years ago.

Scientists suggest that in our galaxy you can find more than half a million asteroids with a diameter of more than 1.5 kilometers. Recent studies have shown that meteorites and asteroids have a similar composition, so asteroids may well be the bodies from which meteorites are formed.

Exploring asteroids

The study of asteroids dates back to 1781, after William Herschel discovered the planet Uranus to the world. At the end of the 18th century, F. Xaver gathered a group of famous astronomers who were looking for a planet. According to Xaver's calculations, it should have been between the orbits of Mars and Jupiter. At first, the search did not give any results, but in 1801, the first asteroid, Ceres, was discovered. But its discoverer was the Italian astronomer Piazzi, who was not even part of the Xaver group. In the next few years, three more asteroids were discovered: Pallas, Vesta and Juno, and then the search stopped. Only 30 years later, Karl Ludovik Henke, who showed interest in the study of the starry sky, resumed their search. Since that period, astronomers have discovered at least one asteroid a year.

Characteristics of asteroids

Asteroids are classified according to the spectrum of reflected sunlight: 75% of them are very dark carbonaceous asteroids of class C, 15% are grayish-siliceous class S, and the remaining 10% are metallic class M and several other rare species.

The irregular shape of the asteroids is also confirmed by the fact that their brightness decreases quite rapidly with increasing phase angle. Due to the large distance from the Earth and their small size, it is rather problematic to obtain more accurate data on asteroids. The force of gravity on an asteroid is so small that it is not able to give them a spherical shape characteristic of all planets. This gravity allows broken asteroids to exist as separate blocks that are held close to each other without touching. Therefore, only large asteroids that have avoided collisions with medium-sized bodies can retain the spherical shape acquired during the formation of the planets.

Asteroids are celestial bodies that were formed due to the mutual attraction of dense gas and dust orbiting our Sun at an early stage of its formation. Some of these objects, like an asteroid, have reached enough mass to form a molten core. At the moment Jupiter reaches its mass, most of the planetosimals (future protoplanets) were split and ejected from the original asteroid belt between Mars and. During this epoch, part of the asteroids was formed due to the collision of massive bodies within the influence of the gravitational field of Jupiter.

Orbit classification

Asteroids are classified according to features such as visible reflections of sunlight and characteristics of their orbits.

According to the characteristics of the orbits, asteroids are combined into groups, among which families can be distinguished. A group of asteroids is considered to be a certain number of such bodies whose orbital characteristics are similar, that is, semiaxis, eccentricity and orbital inclination. A family of asteroids should be considered a group of asteroids that do not just move in close orbits, but are probably fragments of one large body, and were formed as a result of its split.

The largest of the known families may contain several hundred asteroids, while the most compact families may contain up to ten. Approximately 34% of asteroid bodies are members of asteroid families.

As a result of the formation of most groups of asteroids in the solar system, their parent body was destroyed, however, there are also such groups whose parent body survived (for example).

Classification by spectrum

The spectral classification is based on the spectrum of electromagnetic radiation, which is the result of the asteroid reflecting sunlight. Registration and processing of this spectrum makes it possible to study the composition of a celestial body and assign an asteroid to one of the following classes:

• Group of carbon asteroids or C-group. Representatives of this group consist mostly of carbon, as well as elements that were part of the protoplanetary disk of our solar system in the early stages of its formation. Hydrogen and helium, as well as other volatile elements, are practically absent in carbonaceous asteroids, however, the presence of various minerals is possible. Another distinguishing feature of such bodies is their low albedo - reflectivity, which requires the use of more powerful observation tools than in the study of asteroids of other groups. More than 75% of the asteroids in the solar system are representatives of the C-group. The most famous bodies of this group are Hygiea, Pallas, and once - Ceres.
• A group of silicon asteroids or S-group. Asteroids of this type are composed mainly of iron, magnesium and some other rocky minerals. For this reason, silicon asteroids are also called stony asteroids. Such bodies have a fairly high albedo, which allows you to observe some of them (for example, Irida) simply with binoculars. The number of silicon asteroids in the solar system is 17% of the total, and they are most common at a distance of up to 3 astronomical units from the Sun. The largest representatives of the S-group: Juno, Amphitrite and Herculina.

- These are stone and metal objects that revolve around, but are too small in size to be considered planets.
Asteroids range in size from Ceres, which has a diameter of about 1,000 km, to the size of ordinary rocks. Sixteen known asteroids have a diameter of 240 km or more. Their orbit is elliptical, crossing the orbit and reaching the orbit. Most asteroids, however, are contained in the main belt, which is located between the orbits of and . Some have orbits that intersect with Earth, and some have even collided with Earth in the past.
One example is the Barringer meteorite crater near Winslow, Arizona.

Asteroids are materials left over from the formation of the solar system. One theory suggests that they are the remnants of a planet that was destroyed in a collision a long time ago. Most likely, asteroids are material that could not form into a planet. Indeed, if the estimated total mass of all the asteroids were put together into a single object, the object would be less than 1,500 kilometers in diameter, less than half the diameter of our Moon.

Much of our understanding of asteroids comes from studying pieces of space debris that hit the Earth's surface. Asteroids that are on their way to collide with Earth are called meteors. When a meteor enters the atmosphere at high speed, friction heats it up to high temperatures and it burns up in the atmosphere. If the meteor does not burn out completely, what is left falls on the surface of the Earth and is called a meteorite.

At least 92.8 percent of meteorites are composed of silicate (stone), and 5.7 percent are composed of iron and nickel, while the rest are a mixture of these three materials. Stony meteorites are the most difficult to find as they are very similar to terrestrial rocks.

Since asteroids are material from the very early solar system, scientists are interested in studying their composition. Spacecraft that have flown through the asteroid belt have found that the belt is quite thin and the asteroids are separated by large distances.

In October 1991, the Galileo spacecraft approached the asteroid 951 Gaspra and transmitted the first ever high-precision image of the Earth. In August 1993, the Galileo spacecraft made a close approach to the asteroid 243 Ida. It was the second asteroid visited by the spacecraft. Both Gaspra and Ida are classified as S-type asteroids and are composed of metal-rich silicates.

On June 27, 1997, the NEAR spacecraft passed close to asteroid 253 Matilda. This made it possible for the first time to transmit to Earth the general view of a carbon-rich asteroid belonging to the C-type asteroid.

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, 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 from 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 spectral characteristics 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 is the asteroid Apophis, whose diameter is about 300 meters, in a collision with it, an entire city can be destroyed. 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.