How stars differ from planets: details and interesting points. How to see stars and planets near the Sun

Lifeless space is not deserted at all. It combines a huge mass of all kinds of bodies of different nature, size and with different names. Among them are meteors, meteorites, comets, fireballs, planets and stars. Moreover, each of the categories of cosmic bodies within itself is also divided into types, the difference between which can often be understood only by an experienced astronomer. For now, let's try to understand the fundamental principles, for example, how stars differ from planets.

Main difference

The very first, basic and undeniable difference is the ability to glow. Any star necessarily emits light, but the planet does not have this property. Of course, nearby planets also look like luminous specks - Venus can serve as an eloquent example. But this is not her own glow, she is just a "mirror", which reflects the light of the true source - the Sun.

By the way, this is a very good way to distinguish a planet from a star purely visually, without additional optical instruments. If a luminous dot in the night sky “winks”, that is, flickers, you can be sure that this is a star. If the light emanating from a celestial object is even and constant, then it reflects the light of the nearest luminary. And this is the very first and clear sign showing us how the stars differ from the planets.

The second difference stemming from the first

The ability to emit light is characteristic only of very hot surfaces. As an example, consider a metal that does not glow by itself. But if it is heated to the required temperature, the metal object becomes hot and emits light, albeit weakly.

So the second thing that distinguishes stars from planets is the very high temperature of these cosmic bodies. This is what makes the stars glow. Even on the surface of the coldest star, the temperature does not fall below 2000 degrees K. Usually, stellar temperatures are measured in Kelvin, in contrast to the Celsius familiar to us.

Our Sun is much hotter, at different periods its surface heats up to 5000 or even 6000 K. That is, “in our opinion” it will be 4726.85 - 5726.85 ° C, which is also impressive.

Necessary clarification

These temperatures are typical only for stellar surfaces. Another way stars differ from planets is that they are much hotter inside than outside. Even the surface temperatures on some stars reach 6000 K, and in the center of the stars they presumably go off scale for millions of degrees Celsius! So far, there are no opportunities, no necessary equipment, not even a calculation formula with which it would be possible to determine the internal "degrees" of stars.

Dimensions and movement

The sizes of stars and planets differ just as grandiosely. Compared to the heavenly "lanterns", the planets are just grains of sand. And this applies to both weight (mass) and volume. If, instead of the Sun, a medium-sized apple is placed in the middle of free space, then a pea, placed hundreds of meters away, will be needed to indicate the position of the Earth. A comparison of the stars also shows that the volumes of the latter are thousands or even millions of times greater than the volume in space occupied by the former. With a mass of dumb other ratios. The fact is that all the planets are solid bodies. And the stars are mostly gaseous, otherwise, with which the sky-high temperatures of the luminaries are provided, they would simply be impossible.

What is the difference between a planet and a star? A planet, by definition, has a trajectory of motion called an orbit. And it necessarily surrounds the star as more weighty. The star is motionless in the sky. If you have patience and follow a certain part of the sky for several nights, the movement of the planet can be seen even with a weakly armed eye (but at least you won’t be able to do without an amateur telescope).

Additional features

The sizes of stars and planets cannot be determined by eye. But some differences that accurately characterize require even more specific equipment. So, the chemical composition, which is available to determine by accurately tell whether a planet or a star is in front of us. After all, the luminaries are gaseous giants, therefore, they consist of light elements. And the planets include mostly solid components.

An indirect sign may be the presence of a satellite (or even several). They are only found on planets. However, if a satellite is not observed, this does not mean at all that we have a star in front of us - some planets do well without such "neighbors".

Astronomers have another sign of determining whether a newly discovered cosmic body is a planet. The orbit along which it moves should not contain foreign objects, roughly speaking, debris. Satellites are not considered as such, they are quite large in size, otherwise they would have fallen to the surface. This rule was adopted quite recently - in 2006. Thanks to him, Eris, Ceres and - attention! - Pluto is now considered not full, but

Astronomical calculations

Scientists are highly inquisitive. Knowing perfectly well how stars differ from planets, they nevertheless wondered what would happen when the massiveness of the planet exceeded, for example, the size of the Sun. It turned out that such an increase in the size of the planet would lead to a sharp increase in pressure in the core of the cosmic body; then the temperature will reach a million (or several) degrees; nuclear and thermonuclear reactions will begin - and instead of a planet, we will get a newborn star.

Astronomers using the Spitzer telescope discovered dust particles containing elements of cometary matter in the vicinity of the white dwarf G29-38, which made it possible to speculate about the possibility of the existence of comets and planets in the outer orbits of dead stars.

According to the existing theory, white dwarfs are formed from stars similar to our Sun: at one stage of their evolution, stars become red giants, and then over millions of years, as a result of powerful explosions, they turn into white dwarfs. If the star G29-38 used to have planets, then the formation of a red giant should have swallowed them up. But planets and comets orbiting in outer orbits could survive the death of a star.

This hypothesis is confirmed for the first time by the discovery by astronomers of a dust disk orbiting the star G29-38, which became a white dwarf about 500 million years ago. According to scientists, the dust was formed much later than the explosion of the star. This discovery is the first evidence that comets and planets can outlive the stars they orbit. Observations with the Spitzer telescope will make assumptions about the evolution of systems like our solar system.

“It is possible that the dust around the white dwarf G29-38, detected using the Spitzer space telescope, was formed relatively recently. It may be the remains of a comet that broke out of outer orbit and disintegrated under the influence of the gravitational forces of the star,” comments Dr. William Rich (William Reach) from the Spitzer Science Center at the California Institute of Technology in Pasadena.

The reason for the study of the vicinity of the dead star was the discovery by other observatories of a strange source of infrared radiation near G29-38. A powerful Spitzer infrared spectrometer made it possible not only to see in detail this source - a dust disk - but also to determine its molecular structure, which turned out to be similar to that of comets in the solar system, reports SpaceFlightNow.

"We found a large amount of contaminated silicate particles, the size of which suggests that their source was a comet, and not any other space object," says astronomer Marc Kuchner (Marc Kuchner) from the NASA Goddard Space Flight Center in Greenbelt, State Maryland. In our solar system, comets "live" in the cold border regions called the Kuiper belt and the Oort cloud. And only if something distorts their orbits, such as other comets or outer planets, do they begin to make periodic trips to the Sun. For many comets, this voyage ends in death - they either slowly collapse, flying too close to the Sun, or collide with planets, such as comet Schumacher-Levy 9, which fell on Jupiter in July 1994.

Although the most likely source of the dust around G29–38 is a comet, there are other hypotheses. According to one of them, this may be a new protoplanetary disk, emerging around a white dwarf.

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.

You have already guessed that an unexpected discovery was the discovery of the expansion of the Universe, measured by the redshift of lines in the spectra of distant galaxies. And the most long-awaited discovery was by no means a universal scale: in 1995, astronomers proved that the planets revolve not only around the Sun, but also around other stars outside the solar system.

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 few different methods for searching for exoplanets have been proposed, but we will note only those (Table 1) that have already proven 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 of the described instruments - the coronograph and the interferometer - are very sensitive to the influence of the earth's atmosphere, so for successful operation, apparently, they will have to be delivered to near-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 Earth's turbulent 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. . Most recently, this has been 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. You can notice the periodic oscillations of a star 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 star's radial velocity, i.e., to the projection of its full velocity vector onto the observer's line of sight (this is the 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 shutter that cuts off the light of the star, and light filters that transmit mainly the infrared radiation of the planet in the wavelength range of 2–4 microns, which corresponds to a temperature of about 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 tested against new observational material. Calculating the evolution of a protoplanetary disk takes about a week on a good computer, and during this time, observers have time 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 most important events of the past 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.

In "astronomical calendars" you can often see phrases like " The sun will move into the constellation Taurus", "Mercury in superior conjunction with the Sun", etc. It would seem that they have no practical meaning, because next to the Sun in the sky nothing can be seen.

In this photo, you easily recognize the Pleiades, a small, dipper-shaped open star cluster that usually adorns the winter night sky. But what are these rays diverging from below? Light from a street lamp? No, these rays are part of the solar corona, and the Sun itself is very close, behind the bottom edge of the image.

To see the stars next to the Sun, you need to create an artificial eclipse. No, you don't need to block the Sun with a coin. Such an eclipse has already been created and has been going on for almost 20 years. It takes place aboard the SOHO space observatory. The observatory is a joint project between NASA and ESA and was launched by an Atlas II-AS rocket from Cape Canaveral on December 2, 1995.

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 of 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 is a star, i.e. is an accumulation of gas with incredible volumes. It has its own gravity (an interaction characterized by attraction), with the help of which all its components are held. Inside any star, and hence inside the Sun, thermonuclear fusion reactions take place, the product of which is colossal energy.

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 motions of solar matter originate. 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 also includes other elements, but their proportion is very meager.
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 of the 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

Planets are celestial bodies that orbit around a star or its remnants. A large weight allows the planets under the influence of their own gravity to become rounded. However, the size and weight are insufficient to start thermonuclear reactions. Let us analyze in more detail the characteristics of the planets using the examples of some representatives of this category that are part 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 at different times, the distance of a celestial body from the center of the solar system has different indicators - 206 and 249 million km.

Pluto belongs to the category of dwarf planets. Has a stony core. Some researchers admit that it is formed not only from rocks, but may also include ice. It is covered with a frosted mantle. On the surface is frozen water and methane. The atmosphere presumably includes methane and nitrogen.

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.

Uranus is a planet that was discovered with a telescope in 1781. It has a system of rings and a magnetosphere. Inside Uranus is a core made up of metals and silicon. It is surrounded by water, methane and ammonia. Next comes a layer of liquid hydrogen. There is a gaseous atmosphere on the surface.

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. The average temperature is -224°C.
• 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

A satellite is an object located in the Visible Universe, which does not revolve around a star, but around another celestial body under the influence of its gravity and along a certain trajectory. Let us describe some satellites and characteristics of these space 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.

Callisto is one of the many moons of Jupiter. It is the second largest in the category of satellites and ranks first among celestial bodies in terms of the number of craters on the surface.

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.

Oberon or Uranus IV is a natural satellite of Uranus. It is the 9th largest in the solar system. It has no magnetic field and no atmosphere. Numerous craters have been found on the surface, so some scientists consider it to be a rather old satellite.

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

Asteroids are large boulders. They are mainly located in the asteroid belt between the orbits of Jupiter and Mars. They can leave their orbits towards the Earth and the Sun.

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.

Asteroid Matilda is located in the main belt. It has a fairly low speed of rotation around its axis: 1 revolution occurs in 17.5 Earth days. It contains many carbon compounds. The study of this asteroid was carried out using a spacecraft. The largest crater on Matilda has a length of 20 km.

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.

Vesta is a representative of the largest asteroids of the main asteroid belt. It can be observed without using a telescope, i.e. with the naked eye, because the surface of this asteroid is quite bright. If the shape of Vesta were more rounded and symmetrical, then it could be attributed to the dwarf planets.

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

A comet is a small celestial body. Comets orbit around the Sun and are elongated. These objects, approaching the Sun, form a trail consisting of gas and dust. Sometimes he remains in the form of a coma, ie. a cloud that stretches for a huge distance - from 100,000 to 1.4 million km from the comet's nucleus. In other cases, the trail remains in the form of a tail, the length of which can reach 20 million km.

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 Hale-Bopp comet was observed by mankind for almost 18 months, which indicates its long period. It is also called the "Big Comet of 1997". A distinctive feature of this comet is the presence of 3 types of tails. Along with the gas and dust tails, the sodium tail stretches behind it, the length of which reaches 50 million km.

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.

Over the years of studying the solar system, scientists have collected many interesting facts about celestial bodies. Consider those that depend on chemical and physical characteristics:

• 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.

Watch a video about the celestial bodies of the solar system:

The study of the characteristics of celestial bodies allows mankind to make interesting discoveries, substantiate certain patterns, and also expand general knowledge about the Universe.