How stars differ from planets: details and interesting points. Such amazing and beautiful planets

Remember how in Chekhov's story "Kashtanka" the owner of the dog says to her: "Against a man, you are the same as a carpenter against a carpenter"? This is how the stars are in relation to the planets.

Stars

star in astronomy, a celestial body is called, in which thermonuclear reactions take place. These are massive glowing gas (plasma) balls. They are formed from a gas-dust environment (mainly from hydrogen and helium) as a result of gravitational compression. In the depths of stars there is a huge temperature - millions of kelvins, thermonuclear reactions of hydrogen conversion into helium occur (°С = K−273.15). On their surface - thousands of kelvins. Stars are called the main bodies of the universe, because they contain the bulk of the luminous matter in nature. Our Sun is a typical star of spectral class G with a temperature of 5000-6000 K. Spectral classes- classification of stars according to their radiation spectrum, primarily according to the temperature of the photosphere. There are 7 classes in total: O, B, A, F, G, K, M. Within the class, stars are divided into subclasses from 0 (hottest) to 9 (coldest). The sun has spectral type G2 and equivalent photosphere temperature 5780 K.
The star closest to the Sun is Proxima Centauri. It is located 4.2 light years (3.9 1013 km) from the center solar system.
When we look at the starry sky, then in clear weather naked eye in the sky we can see about 6000 stars, 3000 in each hemisphere. All stars visible from the Earth (including those visible in the most powerful telescopes) are in the local group of galaxies.

local group galaxies- a gravitationally bound group of galaxies, including the Milky Way galaxies, the Andromeda galaxy (M31) and the Triangulum galaxy (M33) - it is shown in the picture above.
We will not go into detailed characteristics of the classification of stars, we will only say that the whole variety of types of stars is only a reflection of the quantitative characteristics of stars (such as mass and chemical composition) and the evolutionary stage at which this moment there is a star.

Main sequence stars

This is the most numerous class of stars. Our Sun also belongs to it. This is the place in the chart where the star spends most of its life. Energy losses due to radiation are compensated for by the energy released during nuclear reactions. There are other types of stars.

brown dwarfs

This is a type of star in which nuclear reactions could never compensate for the energy lost to radiation. Their existence was predicted in the middle of the 20th century, based on ideas about the processes occurring during the formation of stars, and in 2004 a brown dwarf was first discovered. To date, a lot of stars of this type have been discovered. Their spectral type is M - T.

white dwarfs

white dwarfs are compact stars with masses comparable to the mass of the Sun, but with radii ~100 and, accordingly, luminosities ~10,000 times less than the solar one. They are deprived of their own sources of thermonuclear energy. White dwarfs begin their evolution as the exposed degenerate cores of red giants that have shed their shell - that is, as the central stars of young planetary nebulae. The temperatures of the photospheres of the cores of young planetary nebulae are extremely high. Large stars (7-10 times heavier than the Sun) at some point “burn” hydrogen, helium and carbon and turn into white dwarfs with an oxygen-rich core. The surface temperature of young white dwarfs - isotropic stellar cores after shell ejection is very high - more than 2105 K, however, it drops quite quickly due to neutrino cooling and radiation from the surface.

red giants

Red giants and supergiants- stars of late spectral types with high luminosity and extended envelopes. Stars in the course of their evolution can reach late spectral classes and high luminosities at two stages of their development: at the stage of star formation and late stages of evolution. The stage at which young stars are observed as red giants depends on their mass - this stage lasts from ~ 103 to ~ 108 years. At this time, the radiation of the star occurs due to the gravitational energy released during compression. With compression, the surface temperature of such stars increases, but, due to a decrease in the size and area of ​​the radiating surface, the luminosity decreases. Ultimately, the reaction of thermonuclear fusion of helium from hydrogen begins in their cores, and the young star enters the main sequence. At the later stages of stellar evolution, after the hydrogen burns out in their interiors, the stars descend from the main sequence and move into the region of red giants and supergiants. Both "young" and "old" red giants have similar characteristics, due to the similarity of their internal structure- they all have a hot dense core and a very rarefied and extended shell.

The sun is a red giant

The Sun is currently a middle-aged star, estimated to be about 4.57 billion years old. The Sun will remain on the Main Sequence for about 5 billion more years, gradually increasing its brightness by 10% every billion years, after which the hydrogen in the core will be depleted. After that, the temperature and density in the solar core will increase so much that helium combustion will begin, and helium will begin to turn into carbon. The size of the Sun will increase by about 200 times, that is, almost to the modern earth's orbit. Mercury and Venus will be engulfed by it and evaporate completely. The earth, if it does not share their fate, will be heated so much that there will be no chance of saving life. The oceans will evaporate long before the Sun transitions to the red giant stage, in about 1.1 billion years.
At the stage of a red giant, the Sun will be approximately 100 million years, after which it will turn into a planetary nebula, and then become a white dwarf.

variable stars

variable star- a star whose brightness changes with time as a result of events occurring in its area physical processes. Strictly speaking, the brightness of any star changes with time to one degree or another. To classify a star as a variable, it is sufficient that the brightness of the star undergo a change at least once.
Variable stars are very different from each other. Changes in brightness may be periodic. The main observational characteristics are the period, the amplitude of the brightness changes, the shape of the light curve and the radial velocity curve.
Note: do not confuse the variability of stars with their twinkling, which occurs due to fluctuations in the air of the earth's atmosphere. Stars do not twinkle when viewed from space.

Wolf-Rayet stars

Wolf-Rayet Stars- a class of stars that are characterized by very high temperature and luminosity; Wolf-Rayet stars differ from other hot stars by the presence in the spectrum of broad emission bands of hydrogen, helium, as well as oxygen, carbon, and nitrogen.

T Tauri stars (T Tauri, T Tauri stars, TTS)- a class of variable stars, named after its prototype T Taurus. They can usually be found near molecular clouds and identified by their variability. The main source of their energy is gravitational compression. The spectrum of T Tauri stars contains lithium, which is absent from the spectra of the Sun and other main sequence stars, as it is destroyed at temperatures above 2,500,000 K.

new stars

new called stars whose luminosity suddenly increases by a factor of ~103-106. All new stars are close binary systems consisting of a white dwarf and a companion star that is on the main sequence or has reached the stage of a red giant in the course of evolution. In such systems, the matter of the outer layers of the companion star flows onto the white dwarf. The composition of the gas falling on the white dwarf is typical of the outer layers of red giants and main sequence stars - more than 90% hydrogen. As hydrogen accumulates in the surface layer and the temperature rises, thermonuclear reactions begin to take place in the hydrogen-rich layer, this is facilitated by the penetration of carbon from the underlying layers of the white dwarf into the degenerate surface layer. Shortly after the flare, a new cycle and accumulation of the hydrogen layer begins, and after a while the flare is repeated. The interval between outbursts ranges from tens of years for repeated novae to thousands of years for classical novae.
New stars are used as distance indicators. Determining the distances of galaxies and clusters of galaxies using novae gives the same accuracy as when using Cepheids.

supernovae

supernovae- these are stars, the brightness of which during a flash increases by tens of stellar magnitudes over several days. At maximum brightness, a supernova is comparable in brightness to the entire galaxy in which it erupted, and can even exceed it. The term "supernovae" was used to refer to stars that flared up much stronger than the so-called "new stars". In fact, neither one nor the other are physically new: already existing stars flare up. But in several historical cases, those stars that were previously almost or completely invisible in the sky flared up, this phenomenon created the effect of the appearance of a new star.

Other types of stars

Hypernova This is a very large supernova. bright blue variables- very bright blue pulsating hypergiants. Ultra-bright X-ray sources- a celestial body with strong X-ray radiation. neutron stars- an astronomical object, which is one of the end products of the evolution of stars, consisting of a neutron core and a relatively thin (∼1 km) crust of degenerate matter containing heavy atomic nuclei. The mass of a neutron star is almost the same as that of the Sun, but the radius is about 10 km. Therefore, the average density of the matter of such a star is several times higher than the density of the atomic nucleus. It is believed that neutron stars are born during supernova explosions.

star systems

star systems can be single and multiple: double, triple, etc. If the system includes more than ten stars, then it is customary to call it star cluster. Double (multiple) stars are very common. According to some estimates, more than 70% of the stars in the galaxy are multiples.

double stars

, or dual system- two gravitationally bound stars circulating in closed orbits around a common center of mass. With help double stars it is possible to find out the masses of stars and build various dependencies. All black hole candidates are in binary systems.

star clusters

star cluster- a group of stars that have a common origin, position in space and direction of movement. Members of such groups are interconnected by mutual attraction. Most of the known clusters are in our galaxy.

globular clusters

globular cluster- a cluster of stars that has a spherical or slightly flattened shape. Their diameter ranges from 20 to 100 parsecs. These are some of the oldest objects in the universe. The typical age of globular clusters is over 10 billion years. Globular clusters are characterized by a high concentration of stars. There are more than 150 globular clusters in the Milky Way, most of which are concentrated towards the center of the galaxy.

open clusters

open cluster- the second class of star clusters. This is a star system, the components of which are located at a sufficiently large distance from each other. In this it differs from globular clusters, where the concentration of stars is relatively high. For this reason, open clusters are very difficult to detect and study. If stars at the same distance from the observer move in the same direction, there is reason to believe that they are part of an open cluster.
The most famous representatives of this class of clusters are Pleiades and Hyades located in the constellation Taurus.

star associations

Star associations- a rarefied cluster of young stars of high luminosity, which differs from other types of clusters in its size. Associations, like open clusters, are unstable. They slowly expand and their components move away from each other.

galaxies

Galaxy is a large collection of stars, interstellar gas and dust, dark matter(a form of matter that does not emit electromagnetic radiation and does not interact with it. This property of this form of matter makes it impossible to directly observe it. However, it is possible to detect the presence of dark matter by the gravitational effects it creates).

How are stars born?

At first, it is a cold rarefied cloud of interstellar gas, which is compressed under the influence of its own gravity. In this case, the gravitational energy is converted into heat. When the temperature in the nucleus reaches several million Kelvin, nucleosynthesis reactions begin (the process of formation of nuclei chemical elements heavier than hydrogen) and the compression stops. In this state, the star stays for most of its life, being on the main sequence of the Hertzsprung-Russell diagram, until the fuel reserves in its core run out. When all the hydrogen in the center of the star turns into helium, the thermonuclear combustion of hydrogen continues on the periphery of the helium core.
During this period, the structure of the star begins to noticeably change. Its luminosity grows, the outer layers expand, while the inner ones, on the contrary, shrink. And for the time being, the brightness of the star also decreases. The surface temperature decreases - the star becomes a red giant. In this state, the star spends much less time than on the main sequence. When the mass of its isothermal helium core becomes significant, it cannot support its own weight and begins to shrink; the temperature rising at the same time stimulates the thermonuclear conversion of helium into heavier elements.
The most massive stars live for a relatively short time - a few million years. The fact of the existence of such stars means that the processes of star formation did not end billions of years ago, but take place in the present era.
Stars, whose mass is many times greater than the mass of the Sun, have huge sizes, high luminosity and temperature for most of their lives. because of high temperature they have a bluish color, and therefore they are called blue supergiants. Most blue supergiants are observed in the region of the Milky Way, i.e., near the plane of the Galaxy, where the concentration of gas and dust interstellar matter is especially high.
Near the plane of the Galaxy, young stars are unevenly distributed. They almost never meet alone. Most often, these stars form open clusters and more rarefied stellar groups. large sizes, called stellar associations, which have dozens, and sometimes hundreds of blue supergiants. The youngest of the star clusters and associations are less than 10 million years old. In almost all cases, these young formations are observed in regions of increased interstellar gas density. This indicates that the process of star formation is associated with interstellar gas.
An example of a star-forming region is the giant gas complex in the constellation Orion. It occupies almost the entire area of ​​this constellation in the sky and includes a large mass of neutral and molecular gas, dust, and a number of bright gaseous nebulae. The formation of stars in it continues at the present time.

planets

Planet(translated from ancient Greek as “wanderer”) is a celestial body orbiting a star or its remnants, massive enough to become rounded under the influence of its own gravity, but not massive enough to start a thermonuclear reaction, and managed to clear the vicinity of its orbit from planetesimals (a celestial body in orbit around a protostar, formed as a result of the gradual increment of smaller bodies, consisting of dust particles of a protoplanetary disk. Continuously attracting new material and accumulating mass, planetesimals form a larger body, while under the influence of gravity, the individual fragments that compose it begin to condense). There are enough articles about the planets of our solar system on our website in the section “About the planets of the solar system”: http://site/index.php/earth/glubini-vselennoy/15-o-planetah.

But there are planets outside the solar system, they are called exoplanets. Exoplanet or extrasolar planet- a planet orbiting a star outside the solar system. The planets are extremely small and dim compared to the stars, and the stars themselves are far from the Sun (the nearest one is at a distance of 4.22 light years). Therefore, for a long time the task of detecting planets near other stars was unsolvable, the first exoplanets were discovered in the late 1980s. Now such planets have begun to be discovered thanks to improved scientific methods. Currently, the existence of 843 exoplanets in 665 planetary systems has been reliably confirmed, of which 126 have more than one planet. Total exoplanets in the Milky Way galaxy according to new data from 100 billion, of which ~ 5 to 20 billion are possibly "Earth-like". About 34 percent of sun-like stars have planets comparable to Earth in the habitable zone.
Planemo- this is a celestial body, whose mass allows it to fall into the range of definition of a planet, that is, its mass is greater than that of small bodies, but insufficient to start a thermonuclear reaction in the image and likeness of a brown dwarf or star.

So All planets revolve around stars. In the solar system, all the planets revolve in their orbits in the direction in which the sun rotates (counterclockwise, when viewed from the side north pole sun).
In addition to the fact that the planets revolve in their orbit around the star, they also rotate around their axis. The period of rotation of the planet around its axis is known as a day. Most of the planets in the solar system rotate on their axis in the same direction as they orbit the sun, counterclockwise when viewed from the north pole of the sun, except for Venus, which rotates clockwise, and Uranus, whose extreme axial tilt generates controversy, which pole is considered south and which north, and whether it rotates counterclockwise or clockwise. However, whatever opinion the parties hold, the rotation of Uranus is retrograde relative to its orbit.
One of the criteria that allows us to define a celestial body as a classical planet is orbital neighborhoods that are clean from other objects. A planet that has cleared its surroundings has accumulated enough mass to collect or, conversely, disperse all the planetesimals in its orbit. That is, the planet orbits its star in isolation (except for its satellites and Trojans), as opposed to sharing its orbit with many objects of similar size. This criterion for planetary status was proposed by the IAU in August 2006. This criterion deprives such bodies of the solar system as Pluto, Eris and Ceres of the status of a classical planet, classifying them as dwarf planets. Despite the fact that this criterion applies so far only to the planets of the solar system, a number of young star systems that are at the stage of a protoplanetary disk have signs of “clean orbits” for protoplanets.

The Austrian physicist Christian Doppler (1803–1853) would be surprised if he knew that, thanks to the physical effect described by him in 1842 and later named after him, the most unexpected astronomical discovery would be made at the beginning of the 20th century, and at the end of the 20th century the most long-awaited discovery in the history of astronomy will take place.

Many ancient authorities were sure that it was impossible in principle to make such a discovery. For example, the great Aristotle believed that the Earth is unique and there are no others like it. But some thinkers expressed the hope of the existence of "extrasolar" planets - remember Giordano Bruno! However, even those who believed in the “multiple worlds” understood that it was technically extremely difficult, if not impossible, to detect planets in the vicinity of the nearest stars. Before the invention of the telescope, such a task was not even posed, and the possibility of the existence of other planetary systems was discussed only speculatively. But even half a century ago, astronomers, armed with already very advanced telescopes, considered the search for exoplanets - planets around other stars - as an irrelevant occupation, as a task for distant descendants.

Indeed, from a technical point of view, the situation looked hopeless. So, in the early 1960s, astronomers and physicists discussed the possibility of detecting three types of hypothetical objects - black holes, neutron stars and exoplanets. True, of these three terms, two have not even been invented yet - these are black holes and exoplanets, but many believed in the existence of objects of this kind themselves. As for black holes, the possibility of their detection generally seemed beyond reason - after all, they are, by definition, invisible. In 1967, by chance, it was possible to detect rapidly rotating neutron stars with a powerful magnetic field - radio pulsars. But this was an unexpected “gift” from radio astronomy that no one expected in the early 1960s. A few years later, accreting X-ray pulsars were discovered - neutron stars that capture matter from a normal neighbor star. And just 30 years after the problem was recognized as “hopeless”, almost simultaneously (1995–96), single cooling neutron stars and planets around other stars were discovered! In a sense, the prediction turned out to be correct: the discoveries of both objects turned out to be equally difficult, but they took place much earlier than expected.

Variety of planets

It is curious that at the same time, in 1996, another type of hypothetical objects was discovered, occupying an intermediate position between stars and planets - brown dwarfs, which differ from giant planets like Jupiter only in that at an early stage of evolution, thermonuclear reaction involving a rare heavy isotope of hydrogen - deuterium, which, however, does not make a significant contribution to the luminosity of the dwarf. And in the same years, numerous small planets were discovered on the periphery of the solar system - in the Kuiper belt. By 1995, it became clear that this area is inhabited by many bodies with a characteristic size of hundreds and thousands of kilometers, some of which are larger than Pluto and have their own satellites. In terms of their masses, Kuiper belt objects filled the gap between planets and asteroids, and brown dwarfs filled the gap between planets and stars. In this regard, it was necessary to precisely define the term "planet".

The upper limit of planetary masses, separating them from brown dwarfs and from stars in general, was determined on the basis of their internal energy source. It is generally accepted that a planet is an object in which nuclear fusion reactions have not occurred in its entire history. As the calculations performed for bodies of normal (i.e., solar) chemical composition show, during the formation of space objects with a mass of more than 13 Jupiter masses ( M Yu) at the end of the stage of their gravitational compression, the temperature in the center reaches several million kelvins, which leads to the development of a thermonuclear reaction involving deuterium. With smaller masses of objects, nuclear reactions do not occur in their depths. Therefore, the mass in 13 M Yu is considered the maximum mass of the planet. Objects with masses from 13 to 70 M Yu are called brown dwarfs. And even more massive ones are stars, in which thermonuclear combustion of the common light isotope of hydrogen occurs. (For reference: 1 M Yu = 318 Earth masses ( M H) = 0.001 solar masses ( M C) \u003d 2 10 27 kg.)

In their external manifestations, brown dwarfs are closer to planets than to stars. In the process of formation, as a result of gravitational contraction, all these bodies are first heated, and their luminosity rapidly increases. Then, after reaching hydrostatic equilibrium and stopping the compression, their surface begins to cool, and the luminosity decreases. For stars, cooling stops for a long time after the onset of thermonuclear reactions and their entry into a stationary regime. In brown dwarfs, cooling slows down only slightly during deuterium burning. And the surface of the planets cools monotonously. As a result, both planets and brown dwarfs virtually cool down over hundreds of millions of years, while low-mass stars stay hot thousands of times longer. Nevertheless, according to a formal feature - the presence or absence of thermonuclear reactions - planets and brown dwarfs are separated from each other.

The lower boundary of planetary masses, separating them from asteroids, also has a physical justification. The minimum mass of a planet is the one at which the pressure of gravity in the bowels of the planet still exceeds the strength of its material. Thus, in its most general form, a "planet" is defined as a celestial body that is massive enough for its own gravity to give it a spheroidal shape, but not massive enough for thermonuclear reactions to take place in its depths. This range of masses extends from approximately 1% of the mass of the Moon to 13 masses of Jupiter, i.e. from 7·10 20 kg to 2·10 28 kg.

However, the very concept of "planet" astronomers divided into several subtypes in connection with the nature of the orbital motion. First, if a body of planetary mass revolves around a larger similar body, then it is called a satellite (an example is our Moon). A planet proper (sometimes called a "classical planet") is defined as an object of the solar system that is massive enough to take on a hydrostatically equilibrium (spheroidal) shape under the influence of its own gravity, and at the same time does not have a body comparable to it next to its orbit mass. Only Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune satisfy these conditions. Finally, a new class of objects in the solar system has been introduced - "dwarf planets", or "dwarf planets". These bodies must satisfy the following conditions: revolve around the Sun; not be a satellite of the planet; have sufficient mass so that the force of gravity exceeds the resistance of matter and the body of the planet has a spheroidal shape; not have such a large mass to be able to clear the vicinity of its orbit from other bodies. The prototype of the dwarf planets was Pluto (diameter 2310 km), and there are five of them so far: in addition to Pluto, these are Eris (2330 km), Haumea (1200 km), Makemake (1400 km) and Ceres (975 × 909 km), previously considered the largest an asteroid.

Thus, in the solar system there are: 1) classical planets; 2) dwarf planets; 3) satellites with a mass of planets (there are about a dozen of them), which can be called "satellite planets". An object with the mass of a planet outside the solar system is called an "exoplanet" or "extrasolar planet". So far, these terms are equal both in terms of frequency of use and in meaning (recall that the Greek prefix exo- means "outside", "outside"). Both of these terms now apply almost without exception to planets gravitationally bound to any star other than the Sun. However, independent planets living in interstellar space have already been found and, possibly, exist in a considerable number. In relation to them, the term "free-floating planets" is usually used.

As of March 14, 2012, the discovery of 760 exoplanets in 609 planetary systems has been confirmed. At the same time, one hundred systems contain at least two planets, and two - at least six. The nearest exoplanet has been found around the star ε Eridani, 10 light-years from the Sun. The vast majority of exoplanets have been discovered using various indirect detection methods, but some have already been observed directly. Most of the exoplanets seen are gas giants like Jupiter and Saturn orbiting close to the star. Obviously, this is due to the limited possibilities of registration methods: a massive planet in a short-period orbit is easier to detect. But every year it is possible to discover less massive and more distant planets from the star. Objects have already been discovered that almost do not differ from the Earth in mass and orbital parameters.

Exoplanet Search Methods

Quite a lot has been proposed. various methods search for exoplanets, but we will note only those (Table 1) that have already proved their worth and briefly discuss them. Other methods are either under development or have not yet yielded results.

Direct observation of exoplanets. The planets are cold bodies, they themselves do not emit light, but only reflect the rays of their sun. Therefore, a planet located far from the star is almost impossible to detect in the optical range. But even if the planet moves near a star and is well illuminated by its rays, it is difficult for us to distinguish it because of the much brighter brilliance of the star itself.

Let's try to look at our solar system from the side, for example, from the nearest star α Centaur to us. The distance to it is 4.34 light years, or 275 thousand astronomical units (recall: 1 astronomical unit = 1 AU = 150 million km - this is the distance from the Earth to the Sun). For the observer there, the Sun will shine as brightly as the star Vega in the earth's sky. And the brightness of our planets will turn out to be very weak and, moreover, strongly dependent on the orientation of the daytime hemisphere of the planet in its direction. Table 2 shows the most "favorable" values ​​of the angular distance of the planets from the Sun and their optical brightness. It is clear that they cannot be realized simultaneously: at the maximum angular distance of the planet from the Sun, its brightness will be approximately half the maximum. As you can see, Jupiter is the leader in detectability, followed by Venus, Saturn and Earth. Generally speaking, the largest modern telescopes could easily detect such dim objects if there were not an extremely bright star in the sky next to them. But for a distant observer, the angular distance of the planets from the Sun is very small, which makes the task of detecting them extremely difficult.

However, astronomers are now creating instruments that will solve this problem. For example, the image of a bright star can be covered with a screen so that its light does not interfere with the search for a nearby planet. Such an instrument is called a stellar coronograph. Another method involves "quenching" the light of a star due to the effect of the interference of its light rays collected by two or more nearby telescopes - the so-called stellar interferometer. Since the star and the planet located next to it are observed in slightly different directions, with the help of a stellar interferometer (by changing the distance between the telescopes or by choosing the right moment of observation) it is possible to achieve almost complete extinction of the light of the star and at the same time - amplification of the light of the planet. Both described instruments - the coronograph and the interferometer - are very sensitive to the influence of the earth's atmosphere, therefore, for successful work, apparently, will have to deliver them to low Earth orbit.

Measuring the brightness of a star. An indirect method of detecting exoplanets - the method of passages - is based on the observation of the brightness of the star, against the background of the disk of which the planet moves. Only for an observer located in the plane of the exoplanet's orbit, it should eclipse its star from time to time. If this is a star like the Sun, and an exoplanet like Jupiter, whose diameter is 10 times smaller than the sun, then as a result of such an eclipse, the brightness of the star will decrease by 1%. This can be seen with a ground-based telescope. But an Earth-sized exoplanet would cover only 0.01% of the star's surface, and such a small decrease in brightness is difficult to measure through a turbulent earth's atmosphere; this requires a space telescope.

The second problem with this method is that the proportion of exoplanets whose orbital plane is precisely oriented to the Earth is very small. In addition, the eclipse lasts several hours, and the interval between eclipses is years. However, passages of exoplanets in front of stars have been repeatedly observed.

There is also a very exotic method of searching for single planets, freely "drifting" in interstellar space. Such a body can be detected by the effect of a gravitational lens that occurs at the moment when an invisible planet passes against the background of a distant star. With its gravitational field, the planet distorts the course of light rays coming from the star to the Earth; like an ordinary lens, it concentrates light and increases the brightness of a star for an earthly observer. This is a very time-consuming method of searching for exoplanets, requiring long-term observation of the brightness of thousands and even millions of stars. But the automation of astronomical observations already allows its use.

For these reasons, the main role in the search for exoplanets like the Earth is assigned to space instruments. Since 2007, the European satellite COROT has been observing, with a 27 cm telescope equipped with a sensitive photometer. The search for planets is carried out by the method of passages. Several giant planets have already been discovered and even one planet, the size of which is only slightly larger than that of the Earth. In 2009, the Kepler satellite (NASA) was launched into a heliocentric orbit with a telescope with a diameter of 95 cm, capable of continuously measuring the brightness of more than 100,000 stars. Hundreds of exoplanets have already been discovered with this telescope.

Measuring the position of a star. Methods that measure the motion of a star caused by the revolution of a planet around it are considered very promising. As an example, consider the solar system again. Massive Jupiter influences the Sun most strongly: in the first approximation, our planetary system can generally be considered as a binary system of the Sun and Jupiter, separated by a distance of 5.2 AU. and circulating with a period of about 12 years around a common center of mass. Since the Sun is about 1000 times more massive than Jupiter, it is the same number of times closer to the center of mass. This means that the Sun, with a period of about 12 years, revolves around a circle with a radius of 5.2 AU / 1000 = 0.0052 AU, which is only slightly larger than the radius of the Sun itself. From the star α Centauri, the radius of this circle is visible at an angle of 0.004 "" . (This is a very small angle: at this angle, we see the thickness of a pencil from a distance of almost 360 km.) But astronomers are able to measure such small angles, and therefore for several decades they have been observing nearby stars in the hope of noticing their periodic “wiggle” caused by the presence of planets. . At the very recent times this was done from the Earth's surface, but the prospects for an astrometric search for exoplanets are, of course, associated with the launch of specialized satellites capable of measuring the positions of stars with an accuracy of milliarcseconds.

Measuring the speed of a star. notice periodic fluctuations stars can be seen not only by changing its apparent position in the sky, but also by changing the distance to it. Consider again the Jupiter-Sun system, which has a mass ratio of 1:1000. Since Jupiter orbits at 13 km/s, the speed of the Sun in its own small orbit around the center of mass of the system is 13 m/s. For a distant observer located in the plane of Jupiter's orbit, the Sun with a period of about 12 years changes its speed with an amplitude of 13 m/s.

To accurately measure the speeds of stars, astronomers use the Doppler effect. It manifests itself in the fact that in the spectrum of a star moving relative to an earthly observer, the wavelength of all lines changes: if the star approaches the Earth, the lines shift to the blue end of the spectrum, if it moves away, to red. At nonrelativistic velocities, the Doppler effect is sensitive only to the radial velocity of the star, i.e., to the projection full vector its velocity to the line of sight of the observer (this is a straight line connecting the observer with the star). Therefore, the speed of the star, and hence the mass of the planet, are determined up to a factor of cos β, where β is the angle between the plane of the planet's orbit and the observer's line of sight. Instead of the exact value of the planet's mass ( M) the Doppler method gives only the lower bound of its mass ( M cos β).

Usually the angle β is unknown. Only in those cases when the passage of the planet across the disk of the star is observed, one can be sure that the angle β is close to zero. Table 3 shows the characteristic values ​​of the Doppler velocity and angular displacement of the Sun under the influence of each of the planets when observed from neighboring stars. Pluto and Eris are present here as representatives of dwarf planets.

As you can see, the influence of the planet causes the star to move at a speed of, at best, a few meters per second. Is it possible to notice the movement of a star at the speed of a pedestrian? Until the end of the 1980s, the error in measuring the speed of an optical star by the Doppler method was at least 500 m/s. But then fundamentally new spectral instruments were developed, which made it possible to increase the accuracy to 10 m/s. This technique made possible the discovery of the first exoplanets with masses greater than that of Jupiter.

Progress towards planets with masses less than that of Jupiter requires an increase in the accuracy of measuring the speed of a star by 10–100 times. Progress in this direction is quite tangible. Now one of the most accurate stellar spectrometers is working on the 3.6-meter telescope of the European Southern Observatory La Silla (Chile). The spectrum of the star is compared in it with the spectrum of a thorium-argon lamp. To eliminate the influence of fluctuations in temperature and air pressure, the entire instrument is placed in a vacuum container, and the light of the star and the reference lamp is supplied to it from the telescope through a fiberglass cable. The accuracy of measuring the speed of stars in this case is 1 m/s. Could Christian Doppler have imagined this?!

Exoplanet discoveries

astrometric search. Historically, the first attempts to detect exoplanets are associated with observations of the position of nearby stars. In 1916, the American astronomer Edward Barnard (1857–1923) discovered that the dim red star in the constellation Ophiuchus was moving rapidly across the sky relative to other stars - by 10 "" in year. Astronomers later named it "Barnard's Flying Star". Although all stars randomly move in space at velocities of 20–50 km/s, when viewed from a large distance, these movements remain almost imperceptible. Barnard's Star is a very ordinary luminary, so it was suspected that the reason for its observed "flight" is not a particularly high speed, but simply an unusual proximity to us. Indeed, Barnard's star was in second place from the Sun after the α Centaur system.

The mass of Barnard's star is almost 7 times less than the mass of the Sun, which means that the influence of its planetary neighbors (if any) should be very noticeable. For more than half a century, since 1938, the American astronomer Peter van de Kamp (1901–1995) has been studying the motion of this star. He measured its position on thousands of photographic plates and stated that the star exhibits an undulating trajectory with an amplitude of wiggles of about 0.02 "" , which means that an invisible satellite revolves around it. It followed from the calculations that the mass of the satellite is slightly larger than the mass of Jupiter, and the radius of its orbit is 4.4 AU. In the early 1960s, this message spread around the world and received a wide response. After all, this was the first decade of practical astronautics and the search for extraterrestrial civilizations, so people's enthusiasm for new discoveries in space was extremely high.

Other astronomers also joined the study of Barnard's star. By 1973, they found out that this star moves smoothly, without hesitation, which means that it does not have massive planets as satellites. Thus, the first attempt to find an exoplanet ended in failure. And the first reliable astrometric detection of an exoplanet took place only in 2009. After 12 years of observing thirty stars with the 5-meter Palomar Telescope, American astronomers Stephen Pravdo and Stuart Shacklan discovered a planet around the tiny variable star "van Bisbroek 10" in the Gliese 752 binary system. This star is one of the smallest in the Galaxy: it is red a dwarf of the spectral class M8, inferior to the Sun by 12 times in mass and 10 times in diameter. And the luminosity of this star is so small that if we replaced our Sun with it, then during the day the Earth would be illuminated as it is now on a lunar night. It is thanks to the small mass of the star that the discovered planet was able to “shake” it to a noticeable amplitude: with a period of about 272 days, the position of the star in the sky changes by 0.006 "" (The fact that this has been measured is a real triumph for ground-based astrometry). The giant planet itself orbits with a semi-major axis of 0.36 AU. (like Mercury) and has a mass of 6.4 M Yu, i.e., it is only 14 times lighter than its star, and in size it is not even inferior to it.

The success of the Doppler method. The first exoplanet was discovered in 1995 by astronomers at the Geneva Observatory Michel Mayor and Didier Queloz, who built an optical spectrometer that determines the Doppler shift of lines with an accuracy of 13 m/s. Curiously, American astronomers led by Geoffrey Marcy had created a similar instrument earlier, and as early as 1987 began systematically measuring the velocities of several hundred stars, but they were not lucky enough to be the first to make the discovery. In 1994, Major and Queloz began measuring the speeds of 142 stars that are closest to us and are similar in characteristics to the Sun. Quite quickly, they discovered the "wiggles" of star 51 in the constellation Pegasus, 49 light-years away from the Sun. The oscillations of this star occur with a period of 4.23 days and, as astronomers concluded, are caused by the influence of a planet with a mass of 0.47 M YU.

This amazing neighborhood puzzled scientists: very close to the star, like two drops of water similar to the Sun, a giant planet rushes around it in just four days; the distance between them is 20 times less than from the Earth to the Sun. Astronomers did not immediately believe in this discovery. After all, the discovered giant planet, due to its proximity to the star, should be heated to 1000 K. "Hot Jupiter"? Nobody expected such a combination. However, further observations confirmed the discovery of this planet. A name was even proposed for her - Epicurus, but it has not yet received recognition. Then other systems were discovered in which the giant planet orbits very close to its star.

"Eclipses" of stars by planets. The walk-through method has also proven to be effective. Now photometric observations of the stars are carried out both from the board of space observatories and from the Earth. All modern photometric instruments have a wide field of view. By simultaneously measuring the brilliance of millions of stars, astronomers greatly increase their chance of detecting a planet's transit across the disk of a star. In this case, as a rule, planets are found that often show an "eclipse" of the star, i.e., have a short orbital period, and hence a compact orbit.

The term "hot Jupiter" has become so familiar that no one was particularly surprised by the discovery in 2009 of a planet (WASP-18b) with a mass of 10 M Yu and circulating in an almost circular orbit at a distance of 0.02 AU. e. from your star. The orbital period of this planet is only 23 hours! Considering that the star has a greater luminosity than the Sun, the temperature of the planet's surface should reach 3800 K - this is no longer just hot, but "hot Jupiter". Due to its proximity to the star and due to its large mass, the planet causes strong tidal disturbances on the surface of the star, which, in turn, slow down the planet and lead to its fall into the star in the future.

Photos of exoplanets

Despite the enormous difficulties, astronomers still managed to photograph exoplanets with the available means! True, these tools were the best of the best: the Hubble Space Telescope and the largest ground-based telescopes. Among the technical tricks are a damper that cuts off the light of a star, and light filtersthat transmit mainly infrared radiation planets in the wavelength range of 2–4 μm, which corresponds to a temperature of approximately 1000 K (in this range, the planet looks more contrasting with respect to the star).

Planet 2M1207b ( left) is the first ever image of an exoplanet. It has a mass of 3 to 10 M Yu i revolves around a brown dwarf of mass 25 M Yu. The angular distance between them is 0.781, which at a distance of 173 light years to this system corresponds to a linear distance of 41 AU. (about the same as from the Sun to Pluto). The image was taken in the near-IR range with the 8.2-meter telescope of the European Southern Observatory (Chile) in 2004

From the beginning of 2004 to March 2012, 31 images of exoplanets were obtained in 27 planetary systems. For example, in the protoplanetary disk surrounding the young star β Pivotsa, a planet is photographed that is very similar to Jupiter, only more massive. The situation there is reminiscent of the young solar system, in which the newborn Jupiter actively influenced the formation of other planets in the circumsolar disk. Astronomers have long dreamed of observing this process "live".

The first image of the planet ( top left) near a normal solar-type star. This star is 490 light years away from us and has a mass of 0.85 M c and a surface temperature of 4060 K. And the planet is 8 times more massive than Jupiter, and its surface temperature is 1800 K (so it glows on its own). The star and planet are probably about 5 million years old. The distance between them in the projection is about 330 AU. f. Photo taken in 2008 in the near-IR range by the Gemini North Telescope (Mauna Kea Observatory, Hawaii)

In late 2008, the Hubble Space Telescope photographed the planet in a dust disk surrounding the bright star Fomalhaut (α Southern Pisces). Although this star shines almost 20 times more powerful than the Sun, it could not illuminate its planet so much that it is visible from Earth. After all, the discovered planet is 115 times farther from Fomalhaut than the Earth is from the Sun. Therefore, astronomers suggest that the planet is surrounded by a giant light-reflecting ring, much larger than Saturn's. In it, apparently, the satellites of this planet are formed, as in the era of the youth of the solar system, the satellites of the giant planets were formed.

No less curious is the photograph of three planets at once near the star HR 8799 in the constellation Pegasus, obtained using the ground-based Keck and Gemini telescopes. This system is about 130 light-years away from us. Each of its planets is almost an order of magnitude more massive than Jupiter, but they move at about the same distances from their star as our giant planets. Projected onto the sky, these distances are 24, 38, and 68 AU. It is very likely that in place of Venus, Earth and Mars, Earth-like planets will be found in that system. But so far it is beyond technical possibilities.

Obtaining direct images of exoplanets is the most important stage in their study. First, it finally confirms their existence. Secondly, the way is open to studying the properties of these planets: their size, temperature, density, surface characteristics. And the most exciting thing is that the deciphering of the spectra of these planets is not far off, which means the clarification of the gas composition of their atmosphere. Exobiologists have long dreamed of such a possibility.

Ahead - the most interesting!

The discovery of the first extrasolar planetary systems was one of the greatest scientific achievements of the 20th century. The most important problem has been solved: now we know for sure that the solar system is not unique, that the formation of planets near stars is a natural stage of evolution. For several centuries, astronomers have been struggling with the mystery of the origin of the solar system. The main problem is that our planetary system still has nothing to compare with. Now the situation has changed: recently, astronomers have discovered an average of 2-3 planetary systems per week. First of all, which is natural, giant planets are noticeable in them, but terrestrial-type planets are already being found. The classification and comparative study of planetary systems becomes possible. This will greatly facilitate the selection of viable hypotheses and the construction of a correct theory of the formation and early evolution of planetary systems, including our solar system.

At the same time, it became clear that our planetary system is atypical: its giant planets, moving in circular orbits outside the "zone of life" (a region of moderate temperatures around the Sun), allow terrestrial planets to exist within this zone for a long time, one of which is Earth - even has a biosphere. Among the discovered exoplanetary systems, most do not have this quality. We understand, of course, that the mass detection of "hot Jupiters" is a temporary phenomenon associated with the limited capabilities of our technology. But the very fact of the existence of such systems is amazing: it is obvious that a gas giant cannot form near a star, but then how did it get there?

In search of an answer to this question, theorists model the formation of planets in circumstellar gas-dust disks and learn a lot in the process. It turns out that the planet during its growth can travel (migrate) across the disk, approaching the star or moving away from it, depending on the structure of the disk, the mass of the planet and its interaction with other planets. These theoretical studies are extremely interesting, since the simulation results can be immediately checked against new observational material. The calculation of the evolution of a protoplanetary disk takes good computer about a week, during which time observers manage to discover a couple of new planetary systems.

It can be said without exaggeration that the discovery of extrasolar planets is a great event in the history of science. Made at the end of the 20th century, in the future it will become one of the major events of the last century, along with the mastery of nuclear energy, spacewalks and the discovery of the mechanisms of heredity. It is already clear that the recently begun XXI century will be the heyday of planetary science - a branch of astronomy that studies the nature and evolution of planets. For several centuries, the laboratory of planetary scientists was limited to a dozen objects in the solar system, and suddenly, in just a few years, the number of available objects increased hundreds of times, and the range of conditions in which they exist turned out to be discouragingly wide. A modern planetary scientist can be likened to a biologist who for many years studied only the flora and fauna of the desert and suddenly ended up in a tropical forest. Now planetary scientists are in a state of mild shock, but soon they will recover and orient themselves in the gigantic variety of newly discovered planets.

The second science, or rather protoscience, which feels the powerful effect of the discovery of planets around other stars, is the biology of extraterrestrial life, exobiology. Considering the pace of discovery and exploration of exoplanets, we can expect that the 21st century will bring us the discovery of biospheres on some of them and will mark the long-awaited and final birth of exobiology, which has so far developed in a latent state due to the lack of a real object of study.

Good visibility on a clear night.

planets

Among the countless stars can be easily distinguished by their brilliance planets, which is translated from ancient Greek - wandering stars. These celestial bodies were so named by the ancient Greeks because from day to day they moved relative to the seemingly motionless stars and in the night sky seemed to be bright luminaries.

Planets of the Universe

As you know, the planets are not at all: they receive light from and move around it in orbits that are close to a circle in shape.

Comets

In very elongated orbits, after a certain period of time, distant guests of our solar system fly from interplanetary spaces - comets, or tailed stars(translated from Greek). The sudden appearance of a comet has always frightened the ignorant man.

They said that devastating bloody wars would begin, troubles, hunger, pestilence would go everywhere, and even the end of the world would come.

Much more often can be observed, especially at the end of summer, august star shower. In the old days, it was believed that every person has his own star in the sky, and when he dies, his star also fades, falls.
The stars certainly don't fall. These are fragments of celestial bodies and disintegrated comets: they heat up to several thousand degrees and begin to glow when they enter the earth's atmosphere.

meteorites

The hot air around the falling bodies also glows. In the event that they do not completely burn out, turning into a hot gas, they fall to the ground heavenly stones, as they used to be called, or meteorites. Sometimes they reach enormous sizes.

The meteorite, which fell in February 1947 in the area of ​​the Sikhote-Alin ridge with a rain of fragments, is believed to have weighed up to one hundred tons. At the site of its fall, I found many deep craters up to 30 meters in diameter. For two years, about 23 tons of meteorite fragments were collected in this area.

The famous Tunguska meteorite, which fell in the summer of 1908 in the remote taiga, near the small village of Vinovara near the river. Podkamennaya Tunguska (Krasnoyarsk Territory), has not yet been found, despite many years of searching. Scientists believe that it exploded as it fell and completely disintegrated into tiny particles. metal dust.

It was indeed discovered during the analysis of the soil in the area of ​​​​the explosion, which was heard for 1000 kilometers. The explosion column rose to a height of at least 20 kilometers and was visible for 750 kilometers in a circle. On a huge area - up to 60 kilometers in diameter - trees were felled, their tops in all directions from the explosion site.

Scientists believe that about 10 tons of meteorite material falls on Earth every day.

Usually, among the dimly twinkling stars, one can distinguish brighter ones - bluish-white, yellow, reddish. Most stars in a wide silver band - Milky Way, which, like a giant hoop, encircles the vault of heaven.

With his penetrating gaze, man penetrated the innermost depths of the universe and finally saw, through powerful telescopes, distant worlds like the Milky Way. It is not difficult to conclude from this what a modest place ours occupies in the universe - infinite in time and space, having neither beginning nor end.

Star - a hot self-luminous ball

On strict astronomical accounting - millions. The stars and planets of the Universe, as they say, are individually counted, entered into special lists, into a catalog, marked on special maps.
Each star - a hot self-luminous ball similar to our sun.

The stars are very far from us. To the nearest star, that's what it's called Proxima, i.e., in Latin, the nearest, - it would take a very, very long time to get even with the help of a rocket. The light from this star to Earth takes four years, according to astronomers.

The speed of light is very high, 300,000 kilometers per second! From this we can draw the following conclusion, if, say, Proxima will fade today, people will observe its last ray in the sky for four whole years.

One hundred and fifty million kilometers separating from, light travels in 8 minutes 18 seconds. How close to us is the Sun compared to its closest neighbor!

The size of the stars is very different. Giant star (from the constellation Cepheus) 2300 times more sun, and baby stars (the Kuiper star) are almost half the size of the Earth.

The temperature of the stars

different and temperature of the stars. The bluish-white stars are the hottest: their surface temperature is 30,000°; on yellow stars it is already cooler - 6000°, and on red stars 3000° and below. Our Sun is a rather weak star, yellow dwarf as astronomers call it.

The birth of the stars

Exploring the heavenly bodies, scientists have made many interesting conclusions about the birth of stars, about their development and chemical composition. The chemical composition of celestial bodies is studied by a special device - a spectroscope. It makes it possible to detect even negligibly small amounts of a substance by the characteristic colored lines of the spectrum.

Spectrum

Spectrum(from the Latin "spectrum") - visible, vision.
An idea of ​​the spectrum can be obtained from the rainbow after the rain. It attracts with subtle transitions from one color to another: from red - through orange, yellow, green, blue and blue - to purple.

You will never forget the place of each color in the spectrum if you remember this little fable:

Every hunter wants to know where the pheasant is sitting.

Here, the initial letter of the word stands for color.

When a beam of light passes through a trihedral glass prism and falls on a sheet of paper or a white wall, a beautiful rainbow strip is also obtained. You will see the same colored stripe on the ceiling or wall if a ray of the sun falls on the edge face of the mirror or the light sparkles with color tints on the faceted balls and pendants of the theatrical chandelier.

Hot solid and liquid bodies, as well as gases under high pressure, form continuous spectra in the form of iridescent stripes, while rarefied gases give, when heated, not a continuous, but a linear spectrum; it consists of separate colored lines characteristic of each substance, separated by dark gaps.

The adaptation of the spectroscope to the telescope made it possible to obtain photographs of the spectra of very distant celestial bodies and draw the conclusion from this that not a single chemical element unknown on Earth has yet been found on them. The same results were given by the chemical analysis of meteorites. Spectral analysis of distant stellar worlds and chemical analysis of meteorites speak convincingly of unity of matter in the universe.

The content of the article:

Celestial bodies are objects located in the Observable Universe. Such objects can be natural physical bodies or their associations. All of them are characterized by isolation, and also represent a single structure bound by gravity or electromagnetism. Astronomy is the study of this category. This article brings to attention the classification of the celestial bodies of the solar system, as well as a description of their main characteristics.

Classification of celestial bodies in the solar system

Each celestial body has special characteristics, such as the method of generation, chemical composition, size, etc. This makes it possible to classify objects by grouping them. Let's describe what are the celestial bodies in the solar system: stars, planets, satellites, asteroids, comets, etc.

Classification of the celestial bodies of the solar system by composition:

• silicate celestial bodies. This group celestial bodies is called silicate, because. the main component of all its representatives are stone-metal rocks (about 99% of the total body weight). The silicate component is represented by such refractory substances as silicon, calcium, iron, aluminum, magnesium, sulfur, etc. There are also ice and gas components (water, ice, nitrogen, carbon dioxide, oxygen, helium hydrogen), but their content is negligible. This category includes 4 planets (Venus, Mercury, Earth and Mars), satellites (Moon, Io, Europa, Triton, Phobos, Deimos, Amalthea, etc.), more than a million asteroids circulating between the orbits of two planets - Jupiter and Mars (Pallas , Hygiea, Vesta, Ceres, etc.). The density index is from 3 grams per cubic centimeter or more.
• Ice celestial bodies. This group is the most numerous in the solar system. The main component is the ice component (carbon dioxide, nitrogen, water ice, oxygen, ammonia, methane, etc.). The silicate component is present in a smaller amount, and the volume of the gas component is extremely small. This group includes one planet Pluto, large satellites (Ganymede, Titan, Callisto, Charon, etc.), as well as all comets.
• Combined celestial bodies. The composition of representatives of this group is characterized by the presence of all three components in large quantities, i.e. silicate, gas and ice. Celestial bodies with a combined composition include the Sun and the giant planets (Neptune, Saturn, Jupiter and Uranus). These objects are characterized by fast rotation.

Characteristics of the star Sun

The sun has a core, around which a radiation zone is formed, where energy transfer occurs. This is followed by a convection zone, in which magnetic fields and motion of solar matter. The visible part of the Sun can be called the surface of this star only conditionally. A more correct formulation is the photosphere or sphere of light.

The attraction inside the Sun is so strong that it takes hundreds of thousands of years for a photon from its core to reach the surface of a star. At the same time, its path from the surface of the Sun to the Earth is only 8 minutes. The density and size of the Sun make it possible to attract other objects in the solar system. The free fall acceleration (gravity) in the surface zone is almost 28 m/s 2 .

The characteristic of the celestial body of the star Sun is as follows:

1. Chemical composition. The main components of the Sun are helium and hydrogen. Naturally, the star includes other elements, but they specific gravity very scanty.
2. Temperature. The temperature value varies significantly in different zones, for example, in the core it reaches 15,000,000 degrees Celsius, and in the visible part - 5,500 degrees Celsius.
3. Density. It is 1.409 g / cm 3. The highest density is noted in the core, the lowest - on the surface.
4. Weight. If we describe the mass of the Sun without mathematical abbreviations, then the number will look like 1.988.920.000.000.000.000.000.000.000.000 kg.
5. Volume. The full value is 1.412.000.000.000.000.000.000.000.000.000 cubic kilograms.
6. Diameter. This figure is 1391000 km.
7. Radius. The radius of the Sun star is 695500 km.
8. Orbit of a celestial body. The sun has its own orbit around the center milky way. A complete revolution takes 226 million years. Scientists' calculations showed that the speed of movement is incredibly high - almost 782,000 kilometers per hour.

Characteristics of the planets of the solar system

Mars is the second most explored planet. It is the 4th in distance from the Sun. Its dimensions allow it to take 7th place in the ranking of the most voluminous celestial bodies in the solar system. Mars has an inner core surrounded by an outer liquid core. Next is the silicate mantle of the planet. And after the intermediate layer comes the crust, which has a different thickness in different parts of the celestial body.

Consider in more detail the characteristics of Mars:

• The chemical composition of the celestial body. The main elements that make up Mars are iron, sulfur, silicates, basalt, iron oxide.
• Temperature. The average is -50°C.
• Density - 3.94 g / cm 3.
• Weight - 641.850.000.000.000.000.000.000 kg.
• Volume - 163.180.000.000 km 3.
• Diameter - 6780 km.
• Radius - 3390 km.
• Acceleration of gravity - 3.711 m / s 2.
• Orbit. Runs around the sun. It has a rounded trajectory, which is far from ideal, because in different time the distance of a celestial body from the center of the solar system has different indicators - 206 and 249 million km.

Pluto has the following characteristics:

1. Compound. The main components are stone and ice.
2. Temperature. The average temperature on Pluto is -229 degrees Celsius.
3. Density - about 2 g per 1 cm 3.
4. The mass of the celestial body is 13.105.000.000.000.000.000.000 kg.
5. Volume - 7.150.000.000 km 3.
6. Diameter - 2374 km.
7. Radius - 1187 km.
8. Acceleration of gravity - 0.62 m / s 2.
9. Orbit. The planet revolves around the Sun, however, the orbit is characterized by eccentricity, i.e. in one period it recedes to 7.4 billion km, in another it approaches 4.4 billion km. The orbital velocity of the celestial body reaches 4.6691 km/s.

The main characteristics of Uranus:

• Chemical composition. This planet is made up of a combination of chemical elements. In large quantities, it includes silicon, metals, water, methane, ammonia, hydrogen, etc.
• Celestial body temperature. average temperature- -224°С.
• Density - 1.3 g / cm 3.
• Weight - 86.832.000.000.000.000.000.000 kg.
• Volume - 68.340.000.000 km 3.
• Diameter - 50724 km.
• Radius - 25362 km.
• Acceleration of gravity - 8.69 m / s 2.
• Orbit. The center around which Uranus revolves is also the Sun. The orbit is slightly elongated. The orbital speed is 6.81 km/s.

Characteristics of satellites of celestial bodies

Deimos, a satellite of Mars, which is considered one of the smallest, is described as follows:

1. Shape - similar to a triaxial ellipsoid.
2. Dimensions - 15x12.2x10.4 km.
3. Weight - 1.480.000.000.000.000 kg.
4. Density - 1.47 g / cm 3.
5. Compound. The composition of the satellite mainly includes stony rocks, regolith. The atmosphere is missing.
6. Acceleration of gravity - 0.004 m / s 2.
7. Temperature - -40°С.

Characteristics of Callisto:

• The shape is round.
• Diameter - 4820 km.
• Weight - 107.600.000.000.000.000.000.000 kg.
• Density - 1.834 g / cm 3.
• Composition - carbon dioxide, molecular oxygen.
• Acceleration of gravity - 1.24 m / s 2.
• Temperature - -139.2 ° С.

Consider the characteristics of Oberon:

1. The shape is round.
2. Diameter - 1523 km.
3. Weight - 3.014.000.000.000.000.000.000 kg.
4. Density - 1.63 g / cm 3.
5. Composition - stone, ice, organic.
6. Acceleration of gravity - 0.35 m / s 2.
7. Temperature - -198°С.

Characteristics of asteroids in the solar system

A prominent representative of this class is Hygiea - one of the largest asteroids. This celestial body is located in the main asteroid belt. You can see it even with binoculars, but not always. It is well distinguishable during the period of perihelion, i.e. at the moment when the asteroid is at the point of its orbit closest to the Sun. It has a dull dark surface.

The main characteristics of Hygiea:

• Diameter - 407 km.
• Density - 2.56 g/cm 3 .
• Weight - 90.300.000.000.000.000.000 kg.
• Acceleration of gravity - 0.15 m / s 2.
• orbital speed. The average value is 16.75 km/s.

The main characteristics of Matilda are as follows:

1. Diameter - almost 53 km.
2. Density - 1.3 g / cm 3.
3. Weight - 103.300.000.000.000.000 kg.
4. Acceleration of gravity - 0.01 m / s 2.
5. Orbit. Matilda completes an orbit in 1572 Earth days.

This asteroid has an iron-nickel core covered with a rocky mantle. The largest crater on Vesta is 460 km long and 13 km deep.

We list the main physical characteristics of Vesta:

• Diameter - 525 km.
• Weight. The value is within 260.000.000.000.000.000.000 kg.
• Density - about 3.46 g/cm 3 .
• Free fall acceleration - 0.22 m / s 2.
• orbital speed. The average orbital velocity is 19.35 km/s. One revolution around the Vesta axis takes 5.3 hours.

Characteristics of solar system comets

Halley is the celestial body of a group of comets, known to mankind since ancient times, because. it can be seen with the naked eye.

Features of Halley:

1. Weight. Approximately equal to 220.000.000.000.000 kg.
2. Density - 600 kg / m 3.
3. The period of revolution around the Sun is less than 200 years. The approach to the star occurs approximately in 75-76 years.
4. Composition - frozen water, metal and silicates.

The composition of the comet: deuterium (heavy water), organic compounds (formic, acetic acid, etc.), argon, crypto, etc. The period of revolution around the Sun is 2534 years. There are no reliable data on the physical characteristics of this comet.

Comet Tempel is famous for being the first comet to have a probe delivered from Earth.

Characteristics of Comet Tempel:

• Weight - within 79.000.000.000.000 kg.
• Dimensions. Length - 7.6 km, width - 4.9 km.
• Compound. Water, carbon dioxide, organic compounds, etc.
• Orbit. Changes during the passage of a comet near Jupiter, gradually decreasing. Recent data: one revolution around the Sun is 5.52 years.

• The largest celestial body in terms of mass and diameter is the Sun, Jupiter is in second place, and Saturn is in third.
• The greatest gravity is inherent in the Sun, the second place is occupied by Jupiter, and the third - by Neptune.
• Jupiter's gravity contributes to the active attraction of space debris. Its level is so high that the planet is able to pull debris from the Earth's orbit.
• The hottest celestial body in the solar system is the Sun - this is no secret to anyone. But the next indicator of 480 degrees Celsius was recorded on Venus - the second planet farthest from the center. It would be logical to assume that Mercury should have the second place, the orbit of which is closer to the Sun, but in fact the temperature indicator there is lower - 430 ° C. This is due to the presence of Venus and the lack of an atmosphere in Mercury, which is able to retain heat.
• The coldest planet is Uranus.
• To the question of which celestial body has the highest density in the solar system, the answer is simple - the density of the Earth. Mercury is in second place and Venus is in third.
• The trajectory of Mercury's orbit provides the length of a day on the planet equal to 58 Earth days. The duration of one day on Venus is 243 Earth days, while the year lasts only 225.