What are the sizes of the terrestrial planets. Characteristics of the terrestrial planets. The structure and similarity of the terrestrial planets

Pluto - they all have small masses and sizes, their average density is several times higher than the density of water; they are able to slowly rotate around personal axes; they have a small number of satellites (Mars has two, Earth has only one, and Venus and Mercury do not have them at all).

The similarity of the planets in the terrestrial group does not exclude some differences. For example, Venus rotates in the opposite direction from its motion around the Sun, and two hundred and forty-three times slower than the Earth. The period of rotation of Mercury (that is, the year of this planet) is only one third longer than the period of its rotation around its axis.

The angle of inclination of the axis to the orbital planes for Mars and Earth is approximately the same, but completely different for Venus and Mercury. Just like the Earth, there are seasons, which means that on Mars, although almost 2 times longer than on Earth.

Perhaps, distant Pluto, the smallest of the nine planets, can also be attributed to the planets of the terrestrial group. Pluto's usual diameter was over two thousand kilometers. Only 2 times smaller than the diameter of Pluto's satellite - Charon. Therefore, it is not a fact that the Pluto-Charon system, like the Earth system, is a double planet.

Similarities and differences are also found in the atmospheres of the terrestrial planets. Venus and Mars have an atmosphere, unlike Mercury, which, however, like the Moon, is practically devoid of it. Venus has a fairly dense atmosphere, mainly composed of sulfur compounds and carbon dioxide. The atmosphere of Mars, on the contrary, is too rarefied and very poor in nitrogen and oxygen. The pressure at the surfaces of Venus is almost a hundred times more, while that of Mars is almost one hundred and fifty times less than at the surfaces of the Earth.

The fever near the surfaces of Venus is quite high (about five hundred degrees Celsius) and remains almost the same all the time. Heat surfaces of Venus is determined by the greenhouse effect. The dense atmosphere releases the rays of the sun, but retains the thermal infrared radiation that comes from heated surfaces. The gas in the atmosphere of the terrestrial group planet is in constant motion. Often during a dust storm that lasts more than one month, a large amount of dust rises into the atmosphere of Mars.

Chapter 8. Terrestrial planets: Mercury, Venus, Earth

Formation of planets

Comparison of the sizes of the terrestrial planets. From left to right: Mercury, Venus, Earth, Mars. Photos from the site: http://commons.wikimedia.org

According to the most common hypothesis, the planets and the Sun were supposedly formed from a single "solar" nebula. According to some scientists, the planets originated after the formation of the Sun. According to another hypothesis, the formation of protoplanets precedes the formation of the protosun. The sun and the planets formed from a vast cloud of dust, consisting of grains of graphite and silicon, as well as iron oxides, frozen with ammonia, methane and other hydrocarbons. Collisions of these grains of sand led to the formation of pebbles up to several centimeters in diameter, scattered over a colossal complex of rings orbiting the Sun. The disk formed from the "solar nebula" possessed, as already mentioned, instability, which led to the formation of several gas rings, which soon turned into giant gas protoplanets. The formation of such a protosun and protoplanets, when the protosun did not yet shine, allegedly had a very significant significance for further evolution. Solar system.

In addition to this hypothesis, there is a hypothesis about the "gravitational capture" of a star by the Sun of a gas-dust nebula, from which all the planets were condensed by the solar system. Some of the material in this nebula has remained free and travels in the solar system in the form of comets and asteroids. This hypothesis was proposed by O.Yu. Schmidt. In 1952, K.A. Sitnikov, and in 1956 - V.M. Alekseev. In 1968 V.M. Alekseev, based on the ideas of academician A.N. Kolmogorov, built a model of complete capture, proving the possibility of this phenomenon. Some modern astrophysicists also adhere to this point of view. But the final answer to the question: "How, from what, when and where the solar system originated" is very far away. Most likely, many factors participated in the formation of the planetary row of the solar system, but planets could not have formed from gas and dust. The giant planets - Saturn, Jupiter, Uranus and Neptune - have rings consisting of stones, sand and ice blocks, but they do not condense into clots and satellites. I can offer an alternative hypothesis explaining the origin of planets and their satellites in the solar system. All these bodies were captured by the Sun into its gravitational trap from the space of the Galaxy, practically already in the formed (finished) form. The solar planetary system was formed (literally assembled) from ready-made cosmic bodies, which in the space of the Galaxy moved in close orbits and in the same direction with the Sun. The gravitational disturbance, which often happens in galaxies, led to their approach to the Sun. It is quite possible that the capture of planets and their satellites by the Sun did not take place just once. It could happen that the Sun captured not individual planets wandering in the vastness of the Galaxy, but entire systems consisting of giant planets and their satellites. It is quite possible that the terrestrial planets were once satellites of the giant planets, but the sun with its powerful gravity tore them from orbits around the giant planets and "forced" to circle only around itself. At this catastrophic moment, the Earth "was able" to capture the Moon in its gravitational trap, and Venus - Mercury. Unlike Earth, Venus could not hold Mercury, and it became the closest planet to the Sun.

One way or another, at the moment there are 8 known planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and several plutonoids, including Pluto, which until recently was listed among the planets. All planets move in orbits in the same direction and in the same plane and in almost circular orbits (with the exception of plutonoids). From the center to the outskirts of the solar system (to Pluto) 5.5 light hours. The distance from the Sun to the Earth is 149 million km, which is 107 of its diameters. The former planets from the Sun are strikingly different in size from the latter and, in contrast to them, are called terrestrial planets, and the distant ones are called giant planets.

Mercury

The planet Mercury, closest to the Sun, is named after the Roman god of commerce, travelers and thieves. This small planet orbits rapidly and rotates very slowly on its axis. Mercury has been known since ancient times, but astronomers did not immediately realize that it was a planet, and that in the morning and in the evening they saw the same star.

Mercury is about 0.387 AU from the Sun. (1 AU is equal to the average radius of the Earth's orbit), and the distance from Mercury to the Earth, as it and the Earth moves along its orbits, varies from 82 to 217 million km. The inclination of the plane of the orbit of Mercury to the plane of the ecliptic (the plane of the solar system) is 7 °. The axis of Mercury is almost perpendicular to the plane of its orbit, and its orbit is elongated. Thus, there is no change of seasons on Mercury, and changes of day and night occur very rarely, about once every two Mercury years. One side of it, facing the Sun for a long time, is very hot, and the other, turned away from the Sun for a long time, is in a terrible cold. Mercury moves around the Sun at a speed of 47.9 km / s. The weight of Mercury is almost 20 times less than the weight of the Earth (0.055M), and the density is almost the same as that of the Earth (5.43 g / cm 3). The radius of the planet Mercury is 0.38R (the radius of the Earth, 2440 km).

Due to the proximity to the Sun under the influence of gravity, powerful tidal forces arose in the body of Mercury, which slowed down its rotation around its axis. In the end, Mercury found itself in a resonant trap. Measured in 1965, the period of its revolution around the Sun was 87.95 Earth days, and the period of rotation around its axis was 58.65 Earth days. Mercury completes three complete revolutions around its axis in 176 days. During the same period, the planet makes two revolutions around the Sun. In the future, the tidal deceleration of Mercury should lead to the equality of its revolution around its axis and revolution around the Sun. Then it will always be turned to the Sun with one side, like the Moon to the Earth.

Mercury has no satellites. Perhaps, once upon a time, Mercury itself was a satellite of Venus, but because of solar gravity, it was "taken" from Venus and became an independent planet. The planet is actually spherical. The acceleration of gravity on its surface is almost 3 times less than that of the Earth (g = 3.72 m / s 2 ).

The proximity to the Sun makes it difficult to observe Mercury. In the sky, it does not move far from the Sun - a maximum of 29 °, from the Earth it is visible either before sunrise (morning visibility), or after sunset (evening visibility).

In its physical characteristics, Mercury resembles the Moon, there are many craters on its surface. Mercury has a very thin atmosphere. The planet has a large iron core, which is a source of gravity and magnetic field, the strength of which is 0.1 of the strength of the Earth's magnetic field. The core of Mercury is 70% of the volume of the planet. The surface temperature ranges from 90 ° to 700 ° K (–180 ° to + 430 ° C). The sunflower equatorial side warms up much more than the polar regions. Varying degree heating the surface creates a difference in the temperature of the rarefied atmosphere, which should cause its movement - the wind.

The main characteristic features of the planets of the solar system are determined by their distance from the sun, the period of revolution around the sun, diameter, mass and volume.

Mercury is the closest planet to the Sun and the smallest planet in the Solar System. In terms of radius, it is inferior to the satellites of Jupiter - Callisto and Ganymede, the satellite of Saturn - Titan and the satellite of Neptune - Triton. Mercury rotates around its axis with a period 1.5 times less than its orbital period. On the illuminated hemisphere of Mercury, the temperature reaches 700 ° K, and on the unlit, night side it can drop to 220 ° K. Television footage conducted by Mariner 10 showed that the surface of Mercury is in many ways similar to the surface of the Moon. According to optical and photoclinometric measurements, Mercury is covered with craters no less than the Moon, if not more. The exact dimensions of Mercury 56 have not yet been established. The radar diameter and mass give an average density of Mercury of 5.46 g / cm 3, the Hertzsprung photoelectric method - 1% more than the radar value. The data obtained indicate a significant role of the metallic phase in its interior.

Numerous studies of the reflectivity of the surface of Mercury indicate a high probability of the presence of significant amounts of FeO in its soil. This conclusion contradicts the accepted hypotheses about the conditions of condensation of Mercury. However, if these data are confirmed, then it will be necessary to consider the removal of FeO to the surface in the composition of pyroxene due to basaltic volcanism. The soil of Mercury is close to that on the lunar heights (- 5.5% FeO), which are known to contain orthopyroxene. The largest depression found on Mercury has a diameter of 1300 km. It is filled with a substance similar to that of the lunar seas. Formations similar to the structures of terrestrial tectonics, plates or large-scale faults are not noticeable. It is assumed that the processes of differentiation of the planet, and it has an iron core, ended at the stage of its accretion.

Venus is closest to Earth in size and average density. The mass of the planet, calculated after the flight of the interplanetary station "Mariner-2", is 0.81485 of the earth's mass. Radar measurements led to the conclusion that Venus v unlike other planets, it rotates in the direction opposite to the direction of its movement around the Sun. According to radar measurements, the solid part of Venus is an uneven surface. Information about the microrelief was obtained from the Venera-8 and Venera-14 descent vehicles. In general, the surface of Venus is much smoother than that of other terrestrial planets. There are separate heights and individual peaks of the mountains. One of the regions (near the equator) with a diameter of about 700 km with a depression in the middle part of 60X90 km, towering 10 km above the neighboring regions, is noteworthy. This uplift is interpreted as a large volcanic structure, similar to terrestrial and Martian continental volcanoes. Venus also has a channel-like depression 1400 km long, 150 km wide and 2 km deep, which can be compared with similar and very widespread “channels” on Mars and partly with the African-Arabian rift system in East Africa. This depression or trough, 850 km to the east, penetrates into a continental-sized plateau, where it meets with a weakly expressed, very narrow, undulating depression. Venus-10 estimated the density of the Venusian rock at 2.8 ± 0.1 g / cm 3, which is typical for the Moon or Earth. The photographs of Venus taken by Venus-9 and Venera-10 showed that the surface at the landing sites is characterized by plate-like and rounded matte-gray massive pebbles. Pebbles are fine-grained with a dark matrix of regolith or soil.

Venus is characterized by: 1) a unique topography with a relief contrasting at a higher spatial frequency, but a lower magnitude than others terrestrial planets(it cannot be said that the magnitude of the relief is not similar to the terrestrial one, just as the surface irregularities are comparable to those that characterize the lunar seas), 2) landscape diversity - crater-like forms found in groups separated from mountain plateaus regions by a large equatorial fault (isolated mountains, apparently, are found everywhere in areas surveyed by earth radars), 3) the presence of three types of volcanoes: some form large single structures comparable to the Tarsis volcano on Mars, others - smaller peaks that are found singly or in groups, and others - plains similar to those on Mars and the Moon, 4) the presence of mountainous terrain and roughly defined lineaments, which obviously indicate the manifestation of compression tectonics, 5) the presence of a large trough at the equator, indicating stretching tectonic activity, 6) radioactivity, which indicates that its breeds are similar to terrestrial ones. "Venera-9" and "Venera-10", apparently, met with basalt rocks, and "Venera-8" - with rocks of granite composition (the former confirm the assumption about the development of volcanism, while the latter give reason to consider the presence of more complex tectonic-volcanic history), 7) the presence of two areas that have undergone geometric changes (the differences between them can be explained by the features of the processes that took place in them, which differed either in time or in the rate of flow or combinations of both; however, in all cases, these processes were active enough to separate large fragments from small ones, roll some pebbles and not touch others and mix all this exotic material; such processes could be both ballistic impact and aeolian processes; Venus is surrounded by a powerful gaseous envelope).

The Earth is the largest of all the inner planets, it has the largest satellite - the Moon. The composition of the nitrogen-oxygen atmosphere of the Earth differs sharply from the atmosphere of other planets. We know an incredible amount about the Earth in comparison with other planets.

Moon - natural satellite Earth, making up 1/81 of its mass and orbiting with average speed 1.02 km / s, or 3680 km / h. The surface of the moon consists of light areas formed by mountain systems and hills, and dark areas - the so-called "seas". The largest "seas" have arbitrary names: Sea of ​​Rains, Sea of ​​Clarity, Sea of ​​Abundance, Sea of ​​Nectar, Ocean of Storms, etc. The entire surface (3.8-10 7 km 2) of the Moon is covered with many funnels of various sizes, the largest of which have received the name of the lunar circuses. In terms of density, the Moon is an almost homogeneous body. It is slightly asymmetrical. Its center of gravity is about 2 km closer to the Earth than its geometric center. On

On the moon, there are highlands, irregular and annular sea basins, lineaments and furrows, craters with a diameter of thousands of kilometers to millimeters. The moon has a very weak seismicity. Obviously, the weak tremors recorded by seismographs on the lunar surface are caused by falling meteorites rather than tectonic activity. However, based on seismic data, four or five zones are identified. The first seismic boundary runs at a depth of 50-60 km, the second - 250 km, the third - 500 km, and the fourth - 1400-1500 km. Corresponding zones are attributed to the crust, upper, middle and lower mantle, and in the center of the Moon, perhaps, there is a core with a diameter of 170-350 km. These subdivisions are rather arbitrary, since the observed differences in the velocities of seismic waves are on the verge of the resolving power of seismographs installed on the Moon.

Of all the inner planets, Mars is the farthest from the Sun, its mass is 0.108 of the mass of the Earth, the compression is 1 / 190.9, that is, it is greater than that of the Earth. This indicates that its mass is less concentrated near the center than on Earth. Mars revolves around the Sun with a period of 1 year 322 proper days, the axis of rotation has an inclination of 67 ° to the orbital plane. This causes the seasons to change at different latitudes, similar to what happens on Earth. Mars has two satellites - Deimos and Phobos - with rotation periods of 30.30 and 7.65 hours, respectively; satellites move almost exactly in the plane of the planet's equator: Phobos at a distance of 9400 km, and Deimos at 23,500 km. According to Mariner-9, the satellites have an irregular shape, the dimensions of Phobos are 25X21 km, and Deimos is 13.5X12 km; both have a low albedo (0.05), which is close in value to that of carbonaceous chondrites and basalts. Phobos and Deimos are covered with numerous impact craters.

The planets belonging to the terrestrial group - Mercury, Venus, Earth, Mars - are small in size and mass, the average density of these planets is several times higher than the density of water; they slowly revolve around their axes; they have few satellites (Mercury and Venus do not have them at all, Mars has two tiny ones, and Earth has one).

Similarities and differences are also found in the study of the atmospheres of the terrestrial planets S.G. Khoroshavina. Concepts of modern natural science. Course of lectures - Rostov-on-Don, 2006.

Mercury

Mercury is the fourth brightest planet: at maximum brightness it is almost as bright as Sirius, only Venus, Mars and Jupiter are brighter than it. However, Mercury is a very difficult object to observe due to its small orbit and, therefore, its proximity to the Sun. For the naked eye, Mercury is a bright point, and in a strong telescope it looks like a crescent or an incomplete circle. Changes in the type (phases) of the planet over time show that Mercury is a ball, on the one hand, illuminated by the Sun, and on the other, completely dark. The diameter of this sphere is 4870 km.

Mercury slowly revolves around its axis, always facing the Sun with one side. Thus, the period of revolution around the Sun (Mercurian year) is about 88 Earth days, and the period of rotation around its axis is 58 days. It turns out that a year passes from the rising of the Sun to its setting on Mercury, that is, 88 Earth days. Indeed, the surface of Mercury is in many ways similar to the surface of the Moon, although we do not know if there are indeed seas and craters on the surface of Mercury. Mercury has a relatively high density among the planets of the solar system - about 5.44 g / cm3. Scientists suggest that this is due to the presence of a massive metal core (presumably from molten iron with a density of up to 10 g / cm3, having a temperature of about 2000 K), containing more than 60% of the planet's mass and surrounded by a silicate mantle and probably 60-100 km thick crust ...

Venus

Venus is observed both as the "evening star" and as the "morning star" - Hesperus and Phosphorus, as they called her in the ancient world. After the sun and the moon, Venus is the brightest celestial body, and at night, objects illuminated by it can cast shadows. Venus is also the planet closest to Earth. She is even called the "sister of the Earth". Indeed, the radius of Venus is almost equal to that of the Earth (0.95), its mass is 0.82 of the mass of the Earth. Venus has been quite well studied by people - both the Soviet AMS of the Venus series and the American Mariners approached the planet. Venus revolves around the Sun in 224.7 Earth days, but with this figure, unlike Mercury, nothing interesting is connected. Very interesting fact associated with the period of rotation of the planet itself around its axis - 243 Earth days (in the opposite direction) and the period of rotation of the powerful Venusian atmosphere, which makes a full revolution around the planet in ... 4 days! This corresponds to a wind speed near the surface of Venus of 100 m / s or 360 km / h! It has an atmosphere first discovered by MV Lomonosov in 1761 during the planet's passage across the sun's disk. The planet is shrouded in a thick layer of white clouds that hide its surface. The presence of thick clouds in the atmosphere of Venus, probably consisting of ice crystals, explains the high reflectivity of the planet - 60% of the incident sunlight is reflected from it. Modern scientists have established that the Venusian atmosphere is 96% carbon dioxide CO2. Nitrogen (almost 4%), oxygen, water vapor, noble gases, etc. (all less than 0.1%) are also present here. The basis of the thick cloud layer, located at an altitude of 50 - 70 km, are small drops of sulfuric acid with a concentration of 75-80% (the rest is water, actively "absorbed" by the acid droplets). There are active volcanoes on Venus, since it is reliably known that seismic and tectonic activity on Venus was very active relatively recently. The internal structure of this pseudo-twin of the Earth is also similar to the structure of our planet.

Earth

Our earth seems to us so large and solid and so important to us that we tend to forget about the modest position it occupies in the family of planets of the solar system. True, the Earth still has a rather thick atmosphere, covering a thin inhomogeneous layer of water, and even a titled satellite with a diameter of about ј of its diameter. However, these special signs of the Earth can hardly serve as a sufficient basis for our cosmic "egocentrism". But, being a small astronomical body, the Earth is the most familiar planet to us. The radius of the globe is R = 6378 km. The rotation of the globe in the most natural way explains the change of day and night, the rising and setting of the stars. Some Greek scientists also guessed about the annual motion of the Earth around the Sun. The annual movement of the Earth moves the observer and thus causes an apparent displacement of closer stars relative to more distant ones. Strictly speaking, the center of gravity of the Earth-Moon system, the so-called barycenter, moves around the Sun; around this center the Earth and the Moon describe their orbits during the month.

Our understanding of internal structure and physical condition the bowels of the globe are based on a variety of data, among which seismological data (the science of earthquakes and the laws of propagation of elastic waves in the globe) are of significant importance. The study of the propagation in the globe of elastic waves arising from earthquakes or from powerful explosions made it possible to discover and study the layered structure of the earth's interior.

The air ocean that surrounds the Earth - its atmosphere - is the arena on which various meteorological phenomena are played out. The earth's atmosphere is mainly composed of nitrogen and oxygen.

The earth's atmosphere is conventionally divided into five layers: the troposphere, stratosphere, mesosphere, ionosphere and exosphere. A great influence on many processes occurring on our planet is exerted by the hydrosphere, or the World Ocean, the surface of which is 2.5 times more area sushi. The earth has a magnetic field. Outside the dense layers of the atmosphere, it is surrounded by invisible clouds of very fast moving high energy particles. These are the so-called radiation belts. The structure and properties of the surface of our planet, its shells and bowels, magnetic field and radiation belts are studied by a complex of geophysical sciences.

Mars

When the American close-range station Mariner 4 first took images of Mars in 1965, those photographs caused a sensation. Astronomers were ready to see anything but the lunar landscape. It was on Mars that those who wanted to find life in space pinned special hopes. But these aspirations did not come true - Mars turned out to be lifeless. According to modern data, the radius of Mars is almost half that of the Earth (3390 km), and in terms of mass, Mars is ten times smaller than the Earth. This planet orbits the Sun in 687 Earth days (1.88 years). Solar days on Mars are practically equal to Earth's --24 hours 37 minutes, and the planet's axis of rotation is tilted to the orbital plane by 25), which allows us to conclude that the change is similar to that of the Earth (for the Earth - 23 seasons.

But all the dreams of scientists about the presence of life on the Red Planet melted after the composition of the atmosphere of Mars was established. To begin with, it should be pointed out that the pressure at the planet's surface is 160 times less than the pressure of the earth's atmosphere. And it consists of 95% carbon dioxide, contains almost 3% nitrogen, more than 1.5% argon, about 1.3% oxygen, 0.1% water vapor, there is also carbon monoxide, traces of krypton and xenon were found. Of course, no life can exist in such a rarefied and inhospitable atmosphere.

The average annual temperature on Mars is about -60, temperature drops during the day cause the strongest dust storms, during which thick clouds of sand and dust rise to heights of 20 km. The composition of the Martian soil was finally revealed during studies of the American descent vehicles Viking-1 and Viking-2. The reddish sheen of Mars is caused by the abundance of iron III oxide (ocher) in its surface rocks. The relief of Mars is quite interesting. There are dark and light regions here, as on the Moon, but unlike the Moon, on Mars, the change in surface color is not associated with a change in altitude: both light and dark regions can be at the same height.

Until now, scientists do not know the nature of the cataclysm that caused global climate changes on Mars, leading to modern conditions.

By studying our solar system for centuries, astronomers have also learned a lot about the types of planets that exist in our universe. Thanks to the discovery of exoplanets, this knowledge has expanded significantly: many of these planets are similar to the one we call our home. True, "similar" does not mean an exact identity: of the many planets discovered, hundreds are considered gas giants, and hundreds - "Earthlike." They are also known as terrestrial planets, and this definition says a lot about the planet.

What is a terrestrial planet? Also known as solid planets, these are celestial bodies composed primarily of silicate rocks and metals and having a solid surface. This distinguishes them from gas giants, which are composed primarily of gases like hydrogen and helium, water and heavy elements in various states.

The terrestrial planets are similar in structure and composition to the planet Earth.

Composition and characteristics

All terrestrial planets have roughly the same structure: a central metallic core, mostly iron, surrounded by a silicate mantle. Such planets have similar surface features, including canyons, craters, mountains, volcanoes and other structures that are dependent on the presence of water and tectonic activity.

Terrestrial planets also have secondary atmospheres that are created by volcanic activity or comet impact. This also distinguishes them from gas giants, whose planetary atmosphere is primary and captured directly from the original solar nebula.

Terrestrial planets are also known for having few or no moons. Venus and Mercury have no satellites, Earth has only one. Mars has two - Phobos and Deimos - but they look more like large asteroids than real satellites. Unlike the gas giants, the terrestrial planets also do not have a system of planetary rings.

Terrestrial planets in the solar system

All the planets found in the inner solar system - Mercury, Venus, Earth and Mars - are bright representatives of the terrestrial group. All of them are composed mostly of silicate rock and metal, which are distributed between a dense metallic core and a silicate mantle. The moon is similar to these planets, but its iron core is much smaller.

Io and Europa are also satellites that are similar in structure to the terrestrial planets. Io's compositional modeling showed that the moon's mantle is composed almost entirely of silicate rocks and iron, and surrounds a core of iron and iron sulfide. Europa, on the other hand, has an iron core that is surrounded by an outer layer of water.

Dwarf planets like Ceres and Pluto, as well as other large asteroids, are similar to terrestrial planets in that they have hard surface... However, they are made more of ice materials than stone.

Exoplanets of the terrestrial group

Most of the planets found outside the solar system were gas giants because they are the easiest to spot. But since 2005, hundreds of potential terrestrial exoplanets have been discovered, thanks in large part to the Kepler space mission. Most of the planets became known as "super-earths" (that is, planets with a mass between Earth and Neptune).

Examples of exoplanets of the terrestrial group, a planet with a mass of 7-9 terrestrial. This planet orbits the red dwarf Gliese 876, located 15 light years from Earth. The existence of three (or four) terrestrial exoplanets was also confirmed between 2007 and 2010 in the Gliese 581 system, another red dwarf about 20 light years from Earth.

The smallest of these, Gliese 581 e, has a mass of only 1.9 Earths, but orbits too close to the star. The other two, Gliese 581 c and Gliese 581 d, as well as the alleged fourth planet Gliese 581 g, are more massive and orbit within the "" star. If this information is confirmed, the system will become interesting for the presence of potentially habitable terrestrial planets.

The first confirmed terrestrial exoplanet Kepler-10b, a planet with a mass of 3-4 Earths, located 460 light years from Earth, was discovered in 2011 during the Kepler mission. In the same year, the Kepler Space Observatory released a list of 1,235 exoplanetary candidates, including six "super-Earths" located within its star's potentially habitable zone.

Since then, Kepler has discovered hundreds of planets ranging in size from the Moon to the great Earth, and many more candidates beyond those sizes.

Scientists have proposed several categories for classifying terrestrial planets. Silicate planets- This is a standard type of terrestrial planets in the solar system, consisting mainly of a silicate solid mantle and a metal (iron) core.

Iron planets- This is a theoretical type of terrestrial planets, which consists almost entirely of iron, which means it is denser and with a smaller radius than other planets of comparable mass. Planets of this type are believed to form in high-temperature regions close to the star, where the protoplanetary disk is rich in iron. Mercury can be an example of such a group: it was formed close to the Sun and has a metal core, which is equivalent to 60-70% of the planetary mass.

Planets without a core- Another theoretical type of terrestrial planets: they consist of silicate rocks, but do not have a metal core. In other words, planets without a core are the opposite of an iron planet. Nuclear-free planets are thought to form farther from the star, where the volatile oxidizer is more abundant. And although we do not have such planets, there is a mass of chondrites - asteroids.

Finally there is carbon planets(the so-called "diamond planets"), a theoretical class of planets that consist of a metal core surrounded by predominantly carbonaceous minerals. Again, there are no such planets in the solar system, but there are an abundance of carbon-saturated asteroids.

Until recently, everything scientists knew about planets - including their formation and the existence of different types - came from studying our own solar system. But with the advancement of exoplanet research, which has seen a powerful surge over the past ten years, our knowledge of planets has grown significantly.

On the one hand, we have come to understand that the size and scale of the planets is much higher than we previously thought. Moreover, we first saw many Earth-like planets (which can also be inhabited) existing in other solar systems.

Who knows what we'll find when we get the opportunity to send probes and manned missions to other terrestrial planets?