Asteroids of the solar system. What are asteroids? Asteroid orbit shape

Dimensions and weights. The sizes of the planets are determined by measuring the angle at which their diameter is visible from the Earth. This method is not applicable to asteroids: they are so small that even through telescopes they seem to be points like stars (hence the name "asteroids", that is, "star-like").

Only the first four asteroids can be distinguished by their disk. The angular diameter of Ceres turned out to be the largest: it reaches 1 » (for Pallas, Juno and Vesta it is several times smaller). The angular dimensions of these asteroids were very accurately measured back in 1890 by E. Barnard at the Lick and Yerk observatories. Having determined at the time of observation the distance to Ceres, Pallas, Juno and Vesta and having made the necessary calculations, Barnard found that their diameters are respectively 770, 490, 190 and 380 km (as you can see, they could all fit in the area occupied by Alaska!) .

How to determine the size of many other, smaller asteroids?

Until very recently, they were estimated on the basis of the brightness of asteroids, and the magnitude of the asteroid was compared with the magnitudes of Ceres, Pallas, Juno and Vesta (the sizes of which were already known). However, the brightness of asteroids changes: firstly, with a change in the distance of the asteroid from the Sun (due to a change in the amount of sunlight falling on the asteroid); secondly, with a change in distance from the Earth (due to a change in the amount of light reaching the Earth, reflected from the asteroid); thirdly, with a change in the phase angle, since as this angle increases, an ever smaller fraction of the illuminated surface of the asteroid becomes visible from the Earth. Therefore, to determine the angular dimensions, it is not the visible stellar magnitudes of asteroids that are compared with each other, but the magnitudes that these asteroids would have if they were “placed” at certain (single) distances from the Sun and Earth and if they were “arranged” so that their phase the angle was zero.

Before the McDonald Review, these reduced magnitudes (also called absolute) were expressed by different observers in their own, incomparable, photometric systems, which gave a wide spread in estimates of the size of asteroids. In the McDonald Survey, for all numbered asteroids, absolute stellar magnitudes were established, already expressed in the unified International Photographic System (the same system was used in the Palomar-Leiden Survey).

True, another seemingly insurmountable difficulty of this method remains: size determinations have to be made under certain assumptions about the reflectivity of asteroids - their albedo. It is usually assumed that the albedo of an asteroid is the same as the average albedo of the four largest asteroids. Meanwhile, it is clear that under the same observational conditions, a small asteroid composed of light, well-reflecting matter may turn out to be brighter than a large, but darker asteroid. Nevertheless, when estimating the size of many asteroids, it is the average albedo that is used even now.

So, if we know the absolute magnitude of the asteroid m a 6 c , then assuming that the albedo of all asteroids is the same, we can easily determine the radius (in kilometers) of the asteroid R by a very simple formula: lg R \u003d 3.245-0.2m a 6 s.

Further, based on the already calculated radius, we can estimate the mass of the asteroid M, if the density of the asteroid matter is known. It is usually believed that it is equal to the average density of the substance of asteroid fragments - meteorites falling from time to time on our Earth. This density g, measured in terrestrial laboratories, is 3.5 g/cm 3 (although there are quite light samples, with a density of about 2 g/cm see 3).

In some cases, it was possible to determine the size of asteroids in a “non-standard” way, for example, when covering stars with them (the nature of this phenomenon is the same as when covering stars with the Moon). One of these occultations occurred on the evening of January 23, 1975 and was observed in the USA. The asteroid Eros, as predicted by B. Marsden, should have covered the star x swan. A coverage strip about 25 km wide was to pass through the cities of Albany, Hartfert, Connecticut, and near the eastern edge of Long Island. 17 observation points were organized, where students of the surrounding colleges and students of astronomical departments were located at a distance of 6-8 km along the coverage strip.

During the covering of Eros (about 9 m) with an angular velocity of 0.2-0.3 ° per hour approached the star % Cygnus, which was much brighter than the asteroid (about 4 m). Suddenly, the light of the star disappeared (an opaque barrier appeared in the path of its rays coming towards us - an asteroid), and after a few seconds the star reappeared (Fig. 3).

From the duration of the coverage, Marsden determined that the apparent diameter of Eros was about 24 km.

How else (besides an estimate by absolute magnitude) can one determine the masses of asteroids? It is fundamentally possible, although very difficult, to calculate the mass of asteroids on the basis of their mutual perturbations (during approaches) that asteroids experience. This method of determining the masses was developed by I. Schubart from the Astronomical Institute in Heidelberg. He applied it to determine the masses of the largest asteroids and obtained that the mass of Ceres is (5.9 ± 0.3) 10 -11 Mc (where Mc - mass of the Sun), mass of Pallas - (1.14±0.22) 10 -11 Mwith. By a similar method, other astronomers obtained that the mass of Vesta is (1.20 ± 0.12) 10 -11 Mwith. Thus, the mass of even the largest asteroid - Ceres - is 5000 times less than the mass of the Earth and 600 times less than the mass of the Moon.

After the asteroid belt became "reachable" for spacecraft, we were able to determine the masses of very small asteroids.

Telescopic equipment installed on space rockets made it possible to determine the stellar magnitudes (and sizes) of asteroid fragments with diameters of several centimeters and decimeters (which are inaccessible to observations from Earth).

Thus, at present, there is information about asteroids of "all ranks" - from large bodies with masses of billions of billions of tons to very small ones that could fit in the palm of your hand. Whole "clouds" of dust are also moving in the asteroid belt, the properties of which are being studied by indirect signs. All this allows us to make a fairly complete picture of the asteroid belt.

Back in the 1950s, the Soviet astronomer I. I. Putilin made calculations of the total number of numbered (that is, with well-known orbits) asteroids. The result is amazing. It turned out that all the asteroids put together would fit in a cube with a side of only about 500 km! Almost half of the volume would be occupied by Ceres with Vesta and Pallas. Another 25% would have been Juno with asteroids up to and including the 100th. The discoveries of subsequent asteroids (all smaller ones) only led to a very slow increase in this “volume” of asteroid matter, and after the 1000th asteroid, the growth of their total “volume” almost completely stopped (Fig. 4). Undiscovered asteroids are probably so small that, despite their huge number, they will not be able to increase this “volume” in any significant way, and, according to estimates, small particles and dust grains are hardly enough to fill the voids between asteroids lying nearby in 500 km cube.

It can be assumed that the total volume of asteroid matter in interplanetary space is approximately 10 23 cm. But asteroids are distributed over a huge volume of interplanetary space, so that there are many cubic kilometers of space per body. Therefore, the probability of a collision of a spacecraft flying through the asteroid belt (for example, on the way to Jupiter) with some even a tiny asteroid is negligible.

If we take the value of 3.5 g/cm 3 (see above) as the average density of asteroid matter, then we get that the total mass of all asteroids is about 3.5 10 23 g - a number that is huge according to our earthly ideas, but negligible according to astronomical scale. (In order to "blind" all the asteroids - known and unknown - it would be necessary to tear off a layer of "only" 500 m thick from the surface of the Earth!)

Recently, I. Schubart determined the mass of asteroid matter from the total perturbations that the largest asteroids experience when moving surrounded by their numerous counterparts. He received the value 3 10 23 g, which is in excellent agreement with the estimate obtained earlier.

Attempts have also been made to determine the effect of the gravitational field of the asteroid belt on the motion of Mars. However, Mars turned out to be too massive for asteroids, and this effect could not be detected, which also confirms the insignificance of the total mass of asteroids. True, it is assumed that near the orbit of Jupiter, massive bodies unknown to us are moving. But it is unlikely that there will be too many of them, and they are unlikely to significantly increase the estimate of the total mass of asteroid material.

What do small sizes lead to? According to the law of universal gravitation, each asteroid attracts other bodies. But how weak is this attraction! On a fairly large asteroid (with a diameter of 200 km), the force of gravity on the surface is 100 times less than on Earth, so that a person, once on it, would weigh less than 1 kg and would hardly feel his weight. Having jumped on an asteroid from a height of a 10-story building, it would have descended to the surface for almost a quarter of a minute, reaching a speed of only about 1.5 m / s at the moment of “landing”. Generally speaking, staying on asteroids is not much different from staying in conditions of complete weightlessness.

The first cosmic velocity on them is quite small: on Ceres - about 500 m / s, and on a kilometer-sized asteroid - only about 1 m / s. The second space velocity is 1.4 times greater, so that, moving at the speed of a car (about 100 km / h), it would be possible to fly forever from an asteroid with a diameter of even 5 km. Is it then surprising that there is no atmosphere on asteroids? Even if some gases were released from the depths of asteroids, the forces of gravity could not hold their molecules, and they should have been forever dispersed in interplanetary space.

In 1973, the absence of atmospheres on asteroids was confirmed by measurements of the spectra of asteroids in the infrared range. The spectra obtained by the American astrophysicist O. Gansen for several large asteroids in the wavelength region of about 12 μm only indicated that the asteroids were slightly warm.

However, in the spectrum of infrared radiation of Ceres there was one peculiarity: just about a wavelength of 12 microns, within a narrow band, a “jump” of radiation almost doubled was confidently noted. Such spectral "bands" of radiation are characteristic of gases, and therefore they are observed in those planets and their satellites that are surrounded by an atmosphere. But Ceres is too small to hold an atmosphere!

To explain this paradox, Hansen put forward a tempting hypothesis: on Ceres there is a continuous evaporation of volatile substances, which should be included (!) in the composition of the substance of its surface. It should be said that among various estimates of the mass and diameter of Ceres, one can choose a pair of values ​​​​of these quantities that will lead to a low estimate of the average density of its matter (about 1 g / cm 3), consistent with the assumption that Ceres is largely composed of ice. However, this assumption seemed so incredible even to Hansen himself that he simply doubted his calculations, considering it necessary to obtain new, more accurate estimates of the mass and volume of Ceres before making a final conclusion. In addition, Hansen's assumption was contradicted by the results of polarimetric observations of Ceres, according to which this asteroid, although it is a very dark object, cannot have too loose structures on the surface, which should have been formed during the evaporation of ice. Thus, the infrared spectral bands of Ceres are still a mystery.

Due to their small size, asteroids have a very angular shape. The insignificant force of gravity on asteroids is not able to give them the shape of a ball, which is characteristic of the planets and their large satellites. In the latter case, a huge force of gravity crushes individual blocks, ramming them. On Earth, high mountains at their soles, as it were, are spreading. The strength of the stone turns out to be insufficient to withstand loads of many tons per 1 cm 2, and the stone at the foot of the mountain, without crushing, without splitting, is compressed from all sides, as if “flowing”, only very slowly.

On asteroids with a diameter of up to 200-300 km, due to the small "weight" of the stone, the phenomenon of such "fluidity" is completely absent, and on the largest asteroids it occurs too slowly, and even then only in their bowels. On the surface of asteroids, huge mountains and depressions remain unchanged, much larger in size than on Earth and other planets (average deviations in either direction from the surface level are about 10 km or more), which is manifested in the results of radar observations of asteroids (Fig. 5).

The irregular shape of asteroids is also confirmed by the fact that their brightness decreases unusually rapidly with increasing phase angle (see footnote on p. 11). Such changes in the brightness of the Moon are well known to us: it is very bright at the full moon, then it shines weaker and weaker, until it disappears completely at the new moon. But for the Moon, these changes occur much more slowly than for asteroids, and therefore they can be fully explained only by a decrease in the fraction of the surface illuminated by the Sun visible from the Earth (shadows from lunar mountains and depressions have little effect on the overall brightness of the Moon). The situation is different with asteroids. Such rapid changes in their brightness cannot be explained by the mere change in the surface of the asteroid illuminated by the Sun. And the main reason (especially for small asteroids) of this nature of the change in brightness lies in the irregular shape of asteroids, due to which some parts of their illuminated surface are shielded from the sun's rays by others.

The irregular shape of asteroids was also observed directly through a telescope. This happened for the first time in 1931, when the small asteroid Eros, moving in a very exotic orbit, which we will discuss later, approached the Earth at an unusually small distance (only 28 million km). Then, through a telescope, they saw that this asteroid looked like a "dumbbell" or an unresolved double star with an angular distance between the components of about 0.18 "; it was even seen that the “dumbbell” was spinning!

In January 1975, Eros came even closer to the Earth - at a distance of 26 million km. He was observed over a large segment of the orbit, and this made it possible to see Eros literally from different sides. A careful analysis of the results of numerous observations of Eros, carried out at different observatories around the world, led to a very interesting discovery.

Eros during observations greatly changed its brilliance - by 1.5 m(i.e., almost four times) with a period of 2 hours and a little (Fig. 6). It was assumed that these brightness changes are due to a change in the cross section of the “dumbbell-shaped” Eros rotating around its axis, visible from the Earth, and that its maximum and minimum cross sections differ exactly by a factor of 4. In this case, the minimum brightness of the asteroid should have been observed at the moment when Eros is facing us with its sharp end. However, everything turned out to be much more complicated. First, contrary to expectations, successive brightness maxima and minima had different shapes and different amplitudes. Analysis of the results of observations, carried out using laboratory modeling of the shape of Eros, showed that the play of light and shadow on the uneven surface of the asteroid should have a great influence on the brightness of Eros. As a result, the minimum brightness of Eros was observed just when the asteroid was facing us with almost its maximum cross section! Moreover, the period of revolution of Eros turned out to be equal to two periods of brightness fluctuation - 5 h 16 min. As it turned out, this asteroid is an elongated body with a length to thickness ratio of approximately 1:2.5. He. rotates around a short axis counterclockwise, and in such a way that the axis almost lies in the plane of its orbit (Eros travels around the solar system, as if lying on its “side”).

Brightness fluctuations caused by the same reason (rotation around their own axes of irregularly shaped bodies) were observed in many asteroids. And what is most interesting, they all rotate in the same direction - counterclockwise. This has been established only in recent years with the help of sensitive electron-optical observation techniques.

The Earth and asteroids move in space in different orbits around the Sun and at different speeds. And although they orbit in one direction, it seems to us from the Earth that asteroids move in the sky among the stars either forward (from right to left when they overtake the Earth), then backward (from left to right when the Earth overtakes them). This different pattern of motion of asteroids also affects the change in their brightness: when asteroids move across the sky from left to right (the Earth overtakes them), the period of change in brightness is slightly shorter.

It is interesting that the period of changes in the brightness of asteroids is quite short and almost the same - with an interval of values ​​from 2-3 to 10-15 hours. What made them rotate so quickly? At one time, a hypothesis was put forward that not very large irregularly shaped asteroids can acquire rotation under the influence of flows of the "solar wind" (particles ejected by the Sun), "blowing" for billions of years. However weak this “wind” may be, it must nevertheless transmit to the asteroids some impulse of momentum, which, due to the irregular shape of the asteroid, is unevenly distributed over the asteroid from different sides of its center of gravity. As a result, a non-zero force appears, the resultant of the pressure forces exerted by the "solar wind" on each 1 cm 2 of the asteroid's surface, and the asteroid begins to rotate (very slowly at first, and then faster and faster).

Calculations show that some asteroids (of very irregular shape) can be spun by the "solar wind" so much that they can even be torn apart by centrifugal forces of rotation. However, this explanation is not suitable for larger asteroids, and one has to assume that they acquired rotation during the period of their formation.

But maybe the brightness fluctuations are due not to an irregular shape, but to the “spotting” of asteroids (if different parts of the surface of asteroids are composed of different substances)? Of course, "spotting" of asteroids is possible, and light and darker areas (of different substances) can probably exist on their surfaces. However, the mere assumption of "spotting" is not enough, and, as has been shown, the nature of the rotation of asteroids cannot be explained with the help of "spotting" alone.

Even in one of the largest asteroids - Vesta, the brightness changes are not associated with "spotting", but with its irregular shape. In 1971, observations of Vesta using electron-optical converters showed that the subsequent maxima and minima of the brightness of this asteroid differ slightly in magnitude, and Vesta's rotation occurs with a period - twice as long as previously thought - 10 hours 41 minutes. The American astrophysicist R. Taylor, having studied the features of the light curves of this asteroid, proposed the following model: Vesta is a triaxial spheroid, one of whose diameters is 15% longer than the other two. Just at its south pole, along the long side, stretches a flattened region that extends no further than 45 degrees latitude and is not visible from the northern hemisphere of Vesta. This area, Taylor believes, could be a huge impact crater (almost 400 km in diameter!).

What are asteroids made of? It has long been observed that the light of asteroids has a yellowish tint, similar to the light of the Moon and Mercury.

Since asteroids shine by reflected sunlight, their color is due, in part, to the reflective properties of the asteroid's surface itself. Therefore, the idea arose to determine what substances it is composed of, comparing the color of asteroids with the color of terrestrial objects and meteorites. One of the first such studies in our country was carried out in the 1930s by the Soviet researcher of meteorites E. L. Krinov. He found that many meteorites have a color similar to the color of certain asteroids. Great progress in the study of the properties of asteroids was made in the late 1960s, when a group of American scientists took up polarimetric studies. Comparing the polarization of light reflected from various terrestrial substances, lunar soil and meteorites, they found that there is a certain relationship between the reflectivity (albedo) of materials and the nature of the polarization of light reflected from these materials.

Partially polarized was also the light coming to us from asteroids. Its analysis allowed scientists to draw important conclusions about the nature of the asteroid surface (Fig. 7).

A large series of polarimetric observations of asteroids was organized in the USA by T. Gerels. It turned out that according to the nature of the surface, asteroids fall into several groups (Fig. 8). The most numerous group with very similar properties turned out to be asteroids, the polarization of light of which is similar to the polarization of light reflected from terrestrial stony substances of light color, consisting mainly of various silicates. Juno fell into this group of asteroids.

The other group turned out to be composed of asteroids with a dark, poorly reflective surface. Their substance is similar to dark basaltic glasses or breccias (clastic rocks) of lunar soil samples, as well as to a dark variety of meteorites and to the substance of the surface of Mars' moon Phobos. Among these dark asteroids was Ceres.

There are few asteroids with intermediate surface characteristics. There are also few asteroids with extreme characteristics (for example, darker and lighter ones).

The polarimetric method made it possible to determine the exact dimensions of asteroids, since it took into account their true (and not average) reflectivity (albedo). First of all, the sizes of the first four asteroids were specified. It turned out that the diameter of Ceres slightly exceeds 1000 km, the diameter of Pallas is about 600 km, Juno is 240 km, and Vesta is 525 km. When the sizes of other asteroids studied by the polarimetric method were also recalculated, it turned out that not only these, but at least six more asteroids, which turned out to be even larger than Juno, can claim the right to be called the largest. All of them have low reflectivity and, despite their large size, give little light. Therefore, when the diameters of asteroids were estimated from their apparent brightness, the sizes of these six turned out to be greatly underestimated. In fact, the diameter of Hygiea (10th asteroid) is 400, Interamnia (704th) is 340, Davids (511th) is 290, Psyche (16th) is 250 km, and Bambergi (324th) and Fortuny (19th) - 240 km (same as Juno).

Fortuna is the darkest object in the solar system. In terms of the amount of reflected light, even crushed black coal can compete with Fortuna.

The brightest objects both among the asteroids and among all the bodies of the solar system in general were Angelina (64th asteroid), reflecting almost half of the light, and Lisa (44th), slightly inferior to Angelina. Slightly darker than Vesta, the reflectivity of which is approximately 1.5-2 times worse than that of Angelina. Due to the high reflectivity of Vesta, being at the same distance from Ceres, it seems to be 20% brighter than it (under the same lighting and observation conditions), and Pallas is twice as bright.

The polarimetric results of determining the true albedo, and consequently, the more correct sizes of asteroids, are also confirmed by another method, which also appeared in the most recent years. This is a radiometric method that was developed and first applied to asteroids by American scientists D. Allen and D. Matson in 1970. It is based on measuring the thermal (infrared) radiation of an asteroid (usually in the wavelength range of 10-20 microns). Large dark asteroids and small bright ones, due to different reflectivity, can have the same magnitude in the visible region of light. As for their brightness in the infrared range, it is greater for large bodies (due to the large size of the radiating surface and due to the higher temperature of dark bodies, which better absorb solar radiation). The ratio of the brightness values ​​of an asteroid in the visible and infrared ranges just characterizes its reflectivity (as well as its size).

Polarimetric observations also showed that the polarization of light from asteroids is much greater than that which could arise from a single reflection of light from their surface. With the help of experiments carried out in laboratories on Earth, it was revealed that the same degree of polarization of light as that of asteroids is obtained when reflected from a surface covered with dust and fragments of stones of various sizes.

Just during the period of the study, it became clear that such a “dusty” surface in the vacuum of space would behave quite differently. This conclusion was made on the basis of an analysis of the properties of the lunar soil. For reasons that are still not entirely clear, dust on the Moon behaves differently from Earth dust: unusually loose structures are formed from it, inside which a beam of light “rushes around” like in a maze, experiencing multiple reflections, and the degree of its polarization becomes very large, much greater, than the degree of polarization of light reflected from terrestrial dust or from asteroids.

Further studies showed that the surface of asteroids, judging by the polarization, must be composed of relatively large stones covered with a very thin layer of dust. As we will see later, this is consistent with the concept of the nature of the surface of asteroids, obtained on the basis of completely different research methods.

Since 1970, the United States began to conduct spectral observations of asteroids, which covered both the visible part of the spectrum and the adjacent infrared range. The radiation spectra of dozens of asteroids were obtained and analyzed (Fig. 9). The results, as with other methods described above, were compared with the results of laboratory studies of terrestrial rocks, lunar and meteorite matter, as well as various pure minerals. The American astrophysicist C. Chapman did a particularly great job of interpreting the data obtained.

At present, from various features of the spectra, in particular, from the absorption bands characteristic of certain minerals and their mixtures, as well as from the degree of light absorption within these spectral bands, it has been possible to determine for many asteroids the nature of the minerals that make up the substance of their surface and, for example, , percentage of iron content. It turns out that most asteroids are composed of iron-magnesian silicates, like most meteorites (though only a few asteroids have the same composition of these silicates).

To the surprise of the researchers, it was found that some asteroids reflect light and polarize it in the same way as metals. Such, for example, are the asteroids Psyche (16th asteroid), Lutetia (21st) and Julia (89th). The existence of "metal" asteroids is also evidenced by iron meteorites falling to Earth. They consist of a "solution" of nickel in iron with small impurities of some other substances. Such was, for example, the well-known Sikhote-Alin meteorite that fell on February 12, 1947 in the Ussuri taiga of Primorsky Krai. A metal block weighing about 100 tons flew into the Earth's atmosphere at a speed of about 15 km / s and, scattering in the atmosphere due to its huge resistance, littered with iron fragments several square kilometers of the earth's surface.

This shows that in the past asteroids were heated to high temperatures, which led to the formation of metal cores, some of which are now exposed and partially fragmented. True, it should be noted that the source of heat necessary for such a remelting is not entirely clear. Calculations show that heat very quickly escapes into outer space from small bodies. Therefore, such a source must be very powerful. Perhaps the decay of radioactive elements played a role here. However, elements such as uranium, thorium and the radioactive isotope of potassium, which apparently ensured the heating and remelting of the matter of the large planets (Mercury, Venus, Earth and Mars), as well as the Moon, decay too slowly and cannot raise the temperature of small asteroids. Therefore, in this case, a radioactive isotope with a sufficiently short half-life is needed, and, moreover, there must be a sufficiently large amount of it (to ensure a large heat release per unit time). Such an isotope, according to scientists, may be a radioactive isotope of aluminum 26 A1. According to calculations, however, it turns out that this isotope was relatively small during the formation of asteroids.

Another such source of heating of asteroids can be the Sun (of course, not with the help of solar rays, but, for example, under the influence of variable electromagnetic fields created in interplanetary space by the "solar wind"). The modern Sun, obviously, does not give such heating. But in the past, at the initial stage of its existence, the Sun is believed to have been much hotter than it is now, and the heating of asteroids could be very strong.

If we plot the dependence of the number of asteroids on their size, then it turns out that the number of asteroids rapidly decreases with an increase in their size (which is generally understandable), but in the range of their sizes of 50-100 km, this discovered dependence changes its character (see below). ). For some reason, the number of asteroids of this size is greater than it should be if we use the dependence characteristic of smaller asteroids. Trying to explain this, K. Chapman suggested that large asteroids underwent complete or partial remelting in the past, after which iron-nickel cores formed inside them, and the "surfaced" silicates formed a shell. If asteroids collided and crushed, then such a shell should easily collapse. When a strong metal core was exposed, crushing, and consequently, the size reduction slowed down, which led to the discovered effect.

temperature of asteroids. No matter how hot the asteroids were in the distant past, they have long cooled down. Now they are cold lifeless blocks flying in interplanetary space, and the sun's rays are not able to heat them up.

It is not difficult to calculate approximately the average temperature of an asteroid. Let us compare the heat fluxes falling on the asteroid and on the Earth. Taking the Sun as a point source, we find that the heat fluxes are inversely proportional to the squares of the distances of the Earth and the asteroid from the Sun. The heated Earth and the asteroid radiate thermal energy into space. Therefore, the temperature of each body is set such that the amount of heat lost for radiation is equal to the amount of heat received by the body from the Sun. Further, using the Stefan-Boltzmann law, the following relation can be obtained: T 4 a /T 4 3 = a 2 3 / a 2 a , where T is the absolute temperature, expressed in degrees Kelvin, and a - the average distance (major axis of the orbit) of the considered body in astronomical units.

The average temperature of the Earth is known. It is 288 K (15°C). Substituting it into the resulting ratio and extracting the fourth root of both sides of the equation, after small transformations we get: T a (K) \u003d 288 root a a.

At Ceres, for example, the temperature (calculated, however, according to a more accurate formula) is 165 K (i.e. - 108 ° C). Approximately at this temperature and at normal atmospheric pressure, ammonia, alcohol, and ether freeze on Earth.

Ceres has recently been added to the list of solar system objects that can be studied with radio telescopes. Using a large radio interferometer at the Green Bank Radio Astronomy Observatory (USA), F. Briggs determined thermal radiation from Ceres at a wavelength of 3.7 cm. Ceres turned out to be a very weak radio source with a flux of 0.0024 Jy. Assuming that the diameter of Ceres is 1025 km, Briggs determined the absolute temperature of Ceres by radio brightness, which turned out to be 160 ± 55 K, which is consistent with the above estimate. This confirms that the radio emission from Ceres is of thermal origin.

Vesta, which, unlike Ceres, is composed of a light, well-reflecting substance, has a lower surface temperature and is only 133 K, since this asteroid uses a smaller part of the solar energy that reaches its surface to heat up. On asteroids moving farther from the Sun, it is even colder. Only in a few asteroids moving in unusual orbits, which can approach the Sun, penetrating even inside the orbit of Mercury, the surface heats up to several hundred degrees Kelvin, and, being incandescent, even begins to glow faintly. However, this does not last long, since the asteroids, following their orbits, again move away from the Sun, quickly cooling down.

Crater formation. For billions of years, asteroids circle around the Sun and collide with each other, and then with the resulting fragments. Collision velocities in the asteroid belt are high - about 5 km / s on average, and therefore the phenomena occurring during these collisions are grandiose. At this speed, each gram of asteroidal matter carries a kinetic energy of the order of 10 11 erg (about 12 kJ, or 3 kcal). When even a small asteroid “smashes” into the surface of its large counterpart, all this energy is instantly released, and “a giant explosion occurs. The layers of asteroids that come into contact at the moment of collision are subjected to such strong compression that they partly turn into gas, partly melt. From the place of impact, shock waves of compression and rarefaction diverge in all directions, which press, crumble and shake the substance. A huge fountain of fragments and dust rise above the asteroid. A crater remains on its surface, and under the crater there is an extensive zone of crushed rocks.

The study of meteorite craters on Earth, explosive and impact experiments (in particular, "bombardment" of targets made of different materials with ultra-high-speed balls), carried out in the USSR and abroad, allow us to draw a number of conclusions about the processes during cratering on asteroids. When, in particular, an asteroid hits a surface composed of large monolithic blocks of rocky matter (for example, a fresh fractured surface formed as a result of crushing during a powerful impact), the speed of the flying fragments should be hundreds of meters per second. If the fall occurs on the surface of an asteroid composed of matter fragmented by numerous previous encounters with other asteroids, the fragments should scatter at much lower speeds (tens of meters per second).

The above estimates are only average speeds. Among the fragments there are always faster ones, flying at speeds even exceeding the speed of the fallen asteroid, and slower ones.

Although the masses of “asteroids are small, they are still able to hold part of the fragments that fly apart at speeds less than the second cosmic velocity, which is about 600 m / s on Ceres, and more than 100 m / s on Juno. Even babies with a diameter of 10 km can hold fragments with a speed of up to 6 m / s.

The American astrophysicist D. Gault, analyzing experimental data on the distribution of velocities of flying fragments, came to the conclusion that for an asteroid with a diameter of 200 km, about 85% of the fragments shot up above it are not able to overcome the attraction of the asteroid and fall again on its surface. Asteroids 100 km across hold about half of their fragments. True, fragments ejected from the crater can fly away from the crater for long distances (flying to the back side of the asteroid) or can even begin to move in near-asteroid orbits. Thus, the appearance of a crater on an asteroid should be accompanied by the creation of a short-term cloud of stones and dust over the entire asteroid - its rocky "atmosphere". After some time, fragments and dust settle in a thin layer on the surface of the asteroid.

It should be noted that the substance of the asteroid colliding with Ceres will be present in this “layer-” in the form of a completely imperceptible impurity, since the volume of the substance ejected from the crater is hundreds and thousands of times larger than the volume of the “fallen” asteroid.

So far, we do not have a single photograph of an asteroid taken at a small distance from its surface using any spacecraft. But can the appearance of asteroids differ significantly from the satellites of Mars - Phobos and Deimos? A series of photographs taken from spacecraft sent to Mars showed that even these tiny bodies (about 15 and 6 km in size), circling near Mars, away from the most densely populated parts of the asteroid belt, were bombarded by asteroid fragments, and all are completely cratered , large and small, with diameters from several kilometers to several tens of meters. Probably, there are also such small ones on them, which could not be seen in the received photographs. Asteroids that fly at least for a short time into the dense parts of the asteroid belt may differ from Phobos and Deimos only in that they will be littered with even more craters.

When crushing asteroids in collisions, whole “clouds” of dust are formed along with large and small fragments. Therefore, it was often assumed that the asteroid belt was literally saturated with it. However, as it turned out, there is no more dust in the asteroid belt than in the inner regions of the solar system, but rather even less. Thus, the asteroid belt must be continuously cleared of dust. It happens like this.

Under the action of the light pressure of the sun's rays, the smallest asteroid dust (dust grains a few micrometers in size) should leave the Solar System along hyperbolic orbits, while larger particles slowly slow down and move to ever smaller orbits relative to the Sun. Many of them settle on Mars, Earth, Venus and Mercury along the way, the rest "die" on the Sun. The asteroid component in interplanetary dust is about 2% (2 10 13 t).

> Asteroids

All 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 should 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. Certainly, 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 chart. 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.

In January 2017, NASA selected two projects, Lucy and Psyche, for the Discovery program. They are scheduled to launch in October 2021. Lucy will travel to the asteroid belt and study 6 Trojans. Psyche will fly to 16 Psyche, a giant metallic asteroid. It is important in that it may turn out to be the core of an ancient planet devoid of crust due to a strong collision.

In 2012, Planetary Resources, Inc. announced a desire to send a device to extract water and material from asteroids. After that, NASA started talking about such aspirations. This is an important point, since the asteroid belt holds a huge amount of precious resources, which equate to 100 billion dollars for every earthling.

Children and schoolchildren of all ages should understand that the fall of asteroids or a comet does not pose a threat to the Earth right now. NASA constantly monitors potentially dangerous space objects, knowing the orbits, distances and exact sizes of large asteroids for several decades and even centuries to come. Be sure to carefully read all the interesting facts about asteroids, as well as view photos and pictures to get to know these objects better.

In terms of mass, asteroids are much lighter than the planets of the solar system, but at the same time they may have satellites. Asteroids do not have their own atmosphere, since they cannot hold it with their weak gravitational field. The shape of the asteroid is wrong.

The word "asteroid" itself comes from a combination of Greek words meaning "like a star", "star" and "appearance". And the concept of "asteroid" was introduced by the English astronomer William Herschel on the basis that, when observed through a telescope, these celestial bodies looked like points of stars, in contrast to the planets, which looked like disks.

Until recently, asteroids were considered "minor planets", specifying that their diameter is less than 1500 km. However, at the XXVI Assembly of the International Astronomical Union in 2006, an updated definition of the concept of "planet" was given, and since then most asteroids have been classified as celestial bodies and are no longer considered planets.

It is believed that the first asteroid Cecera was discovered by accident by an Italian astronomer. Giuseppe Piazzi January 1, 1801, although the orbit of this asteroid was calculated even before that by a group of astronomers led by a German astronomer Franz Xaver.

The method of visual observation, which was used to search for asteroids at the beginning, was replaced by the method of astrophotography. In 1891 a German astronomer Maximilian Wolf first used a new method, the essence of which was to photograph celestial bodies with a long exposure period. In the photographs, the asteroids left short light lines. This method greatly accelerated the discovery of new asteroids.

To date, several thousand celestial bodies of this type have already been discovered and numbered.

It is allowed to give any names to newly discovered asteroids, including in honor of their discoverers, but only after their orbit has been calculated reliably enough. Until then, the asteroid is assigned a serial number.

What is the difference between an asteroid and a meteoroid?

A meteoroid (or meteoroid) is a solid cosmic body that moves in interplanetary space. The main parameter by which they can be distinguished from asteroids is their size. Asteroids, as already mentioned, are bodies with a diameter of more than 30 m, while meteoroids are bodies of much smaller size. In addition, they cannot be compared as space objects in the sense that the laws according to which an asteroid and a meteoroid move in outer space are different.

Is asteroid 2012DA14 dangerous?

Scientists think not.

Asteroid numbered 2012DA14, discovered by Spanish astronomers last year, will approach the Earth at 17,000 km. For comparison, the height at which the artificial satellites of the Earth are located, transmitting television signals, is more than 35 thousand km.

The size of the asteroid is small: diameter - about 45 meters, weight - 130 thousand tons. If it had collided with the Earth, the explosion would have released energy comparable to the explosion of 2.4 megatons of TNT.

However, scientists reassure: this “meeting” does not carry any danger of a collision with the Earth. But it will even be possible to observe the “passage” of a celestial body near the Earth. It will be visible to the inhabitants of Australia and Asia with the help of binoculars, and if the atmosphere is clean enough, then with the naked eye. In Moscow, the flight of the asteroid can be observed using strong binoculars or a small telescope, away from city lights. In principle, as the researchers say, it will be possible to see the celestial phenomenon throughout Russia, except for the easternmost regions, where it will already be dawn by the time the asteroid approaches the Earth.

The asteroid will make its closest approach to Earth at 23.25 Moscow time.

Those who wish will be able to watch the flight of an asteroid through an Internet broadcast on the website NASA.

Is there a danger of a global catastrophe from a collision with an asteroid?

Most of them are located in a belt that stretches between the orbits of Jupiter and. The belt is shaped like a torus, and its density decreases beyond a distance of 3.2 AU.

Until August 24, 2006, Ceres was considered the largest asteroid (975x909 km), but they decided to change its status, giving it the title of a dwarf planet. And the total mass of all objects of the main belt is small - 3.0 - 3.6.1021 kg, which is 25 times less than the mass.

Photo of the dwarf planet Ceres

Sensitive photometers make it possible to study changes in the brightness of cosmic bodies. It turns out a light curve, from the shape of which you can find out the period of rotation of the asteroid and the location of the axis of its rotation. Periodicity is from several hours to several hundred hours. Also, the light curve can help in determining asteroid shapes. Only the largest objects approach the shape of a ball, the rest have an irregular shape.

By the nature of the change in brightness, it can be assumed that some asteroids have satellites, while others are binary systems or bodies that roll over each other's surfaces.

The orbits of asteroids change under the powerful influence of the planets, especially Jupiter influences their orbits. It led to the fact that there are entire zones where small planets are absent, and if they manage to get there, then for a very short time. Such zones, called hatches or Kirkwood gaps, alternate with areas filled with space bodies forming families. The main part of asteroids is divided into families, which are most likely formed fromcrushing larger bodies. These clusters are named after their largest member.

At a distance after 3.2 a.u. two flocks of asteroids are circling in Jupiter's orbit - Trojans and Greeks. One flock (Greeks) overtakes the gas giant, and the other (Trojans) lags behind. These groups move quite steadily, because they are at the "Lagrange points", where the gravitational forces acting on them are equalized. The angle of their divergence is the same - 60°. The Trojans were able to accumulate long after the evolution of various asteroid collisions. But there are other families with very close orbits, formed by the recent breakups of their parent bodies. Such an object is the Flora family, which has about 60 members.

Interaction with the Earth

Not far from the inner edge of the main belt are groups of bodies whose orbits may intersect those of the Earth and the terrestrial planets. The main objects include the groups of Apollo, Amur, Aten. Their orbits are not stable, depending on the influence of Jupiter and other planets. The division into groups of such asteroids is rather arbitrary, because they can move from group to group. Such objects cross the Earth's orbit, which creates a potential threat. About 2000 objects larger than 1 km periodically cross the earth's orbit.

They are either fragments of larger asteroids, or cometary nuclei from which all the ice has evaporated. In 10 - 100 million years, these bodies will definitely fall on the planet that attracts them, or on the Sun.

Asteroids in the Earth's Past

The most famous event of this kind was the fall of an asteroid 65 million years ago, when half of everything living on the planet died. It is believed that the size of the fallen body was about 10 km, and the Gulf of Mexico became the epicenter. On Taimyr, traces of a hundred-kilometer crater were also found (in the bend of the Popigai River). On the surface of the planet, there are about 230 astroblems - large impact ring formations.

Compound

Asteroids can be classified according to their chemical composition and morphology. Determining the size of such a small body as an asteroid in the vast solar system, which, moreover, does not emit light, is extremely difficult. This helps to implement the photometric method - the measurement of the brightness of a celestial body. The properties and nature of the reflected light are used to judge the properties of asteroids. So, using this method, all asteroids were divided into three groups:

1. carbonaceous- type C. Most of them - 75%. They do not reflect light well, but are located on the outside of the belt.
2. Sandy- type S. These bodies reflect light more strongly and are located in the inner zone.
3. metal- type M. Their reflectivity is similar to the bodies of group S, and they are located in the central zone of the belt.

The composition of asteroids is similar, because the latter are actually their fragments. Their mineralogical composition is not diverse. Only about 150 minerals have been identified, while there are more than 1000 on Earth.

Other asteroid belts

Similar space objects also exist outside the orbit. There are quite a lot of them in the peripheral parts of the solar system. Beyond the orbit of Neptune is the Kuiper belt, which contains hundreds of objects ranging in size from 100 to 800 km.

Between the Kuiper belt and the main asteroid belt is another collection of similar objects belonging to the "class of Centaurs". Their main representative was the asteroid Chiron, which sometimes pretends to be a comet, becoming covered in a coma and spreading its tail. This two-faced type is 200 km in size and is proof that there are many similarities between comets and asteroids.

Origin hypotheses

What is an asteroid - a fragment of another planet or protosubstance? This is still a mystery, which they have been trying to solve for a long time. There are two main hypotheses:

Planet explosion. The most romantic version is the exploded mythical planet Phaeton. It was allegedly inhabited by intelligent beings who had reached a high standard of living. But a nuclear war broke out, eventually destroying the planet. But the study of the structure and composition of meteorites revealed that the substance of only one planet is not enough for such a variety. And the age of meteorites - from a million to hundreds of millions of years - shows that the fragmentation of asteroids was long. And the planet Phaeton is just a beautiful fairy tale.

Collisions of protoplanetary bodies. This hypothesis prevails. It quite reliably explains the origin of asteroids. The planets formed from a cloud of gas and dust. But in the areas between Jupiter and Mars, the process ended with the creation of protoplanetary bodies, from the collision of which asteroids were born. There is a version that the largest of the small planets are precisely the embryos of the planet that failed to form. Such objects include Ceres, Vesta, Pallas.

largest asteroids

Ceres. It is the largest object in the asteroid belt, with a diameter of 950 km. Its mass is almost a third of the total mass of all the bodies of the belt. Ceres is composed of a rocky core surrounded by an icy mantle. It is assumed that there is liquid water under the ice. A dwarf planet revolves around the Sun in 4.6 years at a speed of 18 km / s. Its rotation period is 9.15 hours, and the average density is 2 g/cm 3 .

Pallas. The second largest object in the asteroid belt, but with the transfer of Ceres to the status of a dwarf planet, became the largest asteroid. Its parameters are 582x556x500 km. The flyby of the star takes 4 years at a speed of 17 km / s. A day on Pallas is 8 hours, and the surface temperature is 164°K.

Vesta. This asteroid has become the brightest and the only one that can be seen without the use of optics. The dimensions of the body are 578x560x458 km, and only the asymmetric shape does not allow Vesta to be classified as a dwarf planet. Inside it is an iron-nickel core, and around it is a stone mantle.

There are many large craters on Vesta, the largest of which has a diameter of 460 km and is located in the region of the south pole. The depth of this formation reaches 13 km, and its edges rise above the surrounding plain by 4–12 km.

Evgenia. This rather large asteroid with a diameter of 215 km. Interesting in that it has two satellites. They were The Little Prince (13 km) and S/2004 (6 km). They are 1200 and 700 km away from Evgenia, respectively.

Study of

The beginning of a detailed study of asteroids was laid by the Pioneer spacecraft. But the first to take pictures of the objects Gaspra and Ida was the Galileo apparatus in 1991. A detailed examination was also carried out by the NEAR Shoemaker and Hayabusa apparatus. Their target was Eros, Matilda and Itokawa. Soil particles were even delivered from the latter. In 2007, the Dawn station departed for Vesta and Ceres, reaching Vesta on July 16, 2011. This year the station should arrive at Ceres, and then it will try to reach Pallas.

It is unlikely that any life will be found on asteroids, but there are certainly many interesting things there. You can expect a lot from these objects, but you don’t want only one thing: their unexpected arrival to visit us.