Everything about the terrestrial planets. What are “terrestrial planets”

Introduction

Among the numerous celestial bodies studied by modern astronomy, planets occupy a special place. After all, we all know well that the Earth on which we live is a planet, so planets are bodies basically similar to our Earth.

But in the world of planets we will not find even two completely similar to each other. The variety of physical conditions on planets is very great. The distance of the planet from the Sun (and therefore the amount of solar heat and surface temperature), its size, the tension of gravity on the surface, the orientation of the axis of rotation, which determines the change of seasons, the presence and composition of the atmosphere, internal structure and many other properties are different for everyone nine planets of the solar system.

By talking about the variety of conditions on the planets, we can gain a deeper understanding of the laws of their development and find out their relationship between certain properties of the planets. So, for example, its ability to retain an atmosphere of one composition or another depends on the size, mass and temperature of a planet, and the presence of an atmosphere, in turn, affects the thermal regime of the planet.

As the study of the conditions under which the origin and further development of living matter is possible shows, only on planets can we look for signs of the existence of organic life. This is why the study of planets, in addition to being of general interest, is of great importance from the point of view of space biology.

The study of planets is of great importance, in addition to astronomy, for other areas of science, primarily the Earth sciences - geology and geophysics, as well as for cosmogony - the science of the origin and development of celestial bodies, including our Earth.

The terrestrial planets include the planets: Mercury, Venus, Earth and Mars.

Mercury.

General information.

Mercury is the planet closest to the Sun in the solar system. The average distance from Mercury to the Sun is only 58 million km. Among the large planets, it has the smallest dimensions: its diameter is 4865 km (0.38 the diameter of the Earth), mass is 3.304 * 10 23 kg (0.055 the mass of the Earth or 1:6025000 the mass of the Sun); average density 5.52 g/cm3. Mercury is a bright star, but it is not so easy to see it in the sky. The fact is that, being close to the Sun, Mercury is always visible to us not far from the solar disk, moving away from it either to the left (to the east), or to the right (to the west) only a short distance that does not exceed 28 O. Therefore, it can be seen only on those days of the year when it moves away from the Sun at its greatest distance. Let, for example, Mercury move away from the Sun to the left. The sun and all the luminaries in their daily movement float across the sky from left to right. Therefore, first the Sun sets, and a little over an hour later Mercury sets, and we must look for this planet low above the Western horizon.

Movement.

Mercury moves around the Sun at an average distance of 0.384 astronomical units (58 million km) in an elliptical orbit with a large eccentricity of e-0.206; at perihelion the distance to the Sun is 46 million km, and at aphelion 70 million km. The planet makes a complete orbit around the Sun in three Earth months or 88 days at a speed of 47.9 km/sec. Moving along its path around the Sun, Mercury at the same time rotates around its axis so that the same half of it always faces the Sun. This means that it is always day on one side of Mercury, and night on the other. In the 60s Using radar observations, it was established that Mercury rotates around its axis in the forward direction (i.e., as in orbital motion) with a period of 58.65 days (relative to the stars). The duration of a solar day on Mercury is 176 days. The equator is inclined to the plane of its orbit by 7°. The angular speed of Mercury's axial rotation is 3/2 the orbital speed and corresponds to the angular speed of its movement in the orbit when the planet is at perihelion. Based on this, it can be assumed that the rotation speed of Mercury is due to tidal forces from the Sun.

Atmosphere.

Mercury may have no atmosphere, although polarization and spectral observations indicate the presence of a weak atmosphere. With the help of Mariner 10, it was established that Mercury has a highly rarefied gas shell, consisting mainly of helium. This atmosphere is in dynamic equilibrium: each helium atom stays in it for about 200 days, after which it leaves the planet, and another particle from the solar wind plasma takes its place. In addition to helium, an insignificant amount of hydrogen has been found in the atmosphere of Mercury. It is about 50 times less than helium.

It also turned out that Mercury has a weak magnetic field, the strength of which is only 0.7% of the Earth's. The inclination of the dipole axis to the rotation axis of Mercury is 12 0 (for the Earth it is 11 0)

The pressure at the surface of the planet is approximately 500 billion times less than at the surface of the Earth.

Temperature.

Mercury is much closer to the Sun than the Earth. Therefore, the Sun shines on it and warms 7 times stronger than ours. On the day side of Mercury it is terribly hot, there is eternal heat. Measurements show that the temperature there rises to 400 O above zero. But on the night side there should always be severe frost, which probably reaches 200 O and even 250 O below zero. It turns out that one half of it is a hot stone desert, and the other half is an icy desert, perhaps covered with frozen gases.

Surface.

From the flyby path of the Mariner 10 spacecraft in 1974, over 40% of the surface of Mercury was photographed with a resolution of 4 mm to 100 m, which made it possible to see Mercury in much the same way as the Moon in the dark from Earth. The abundance of craters is the most obvious feature of its surface, which at first impression can be likened to the Moon.

Indeed, the morphology of the craters is close to the lunar one, their impact origin is beyond doubt: most of them have a defined shaft, traces of ejections of material crushed during the impact, with the formation in some cases of characteristic bright rays and a field of secondary craters. In many craters, a central hill and a terraced structure of the inner slope are distinguishable. It is interesting that not only almost all large craters with a diameter of over 40-70 km have such features, but also a significantly larger number of smaller craters, in the range of 5-70 km (of course, we are talking about well-preserved craters here). These features can be attributed both to the greater kinetic energy of the bodies falling onto the surface, and to the surface material itself.

The degree of erosion and smoothing of craters varies. In general, Mercury craters are less deep compared to lunar ones, which can also be explained by the greater kinetic energy of meteorites due to the greater acceleration of gravity on Mercury than on the Moon. Therefore, the crater that forms upon impact is more efficiently filled with the ejected material. For the same reason, secondary craters are located closer to the central one than on the Moon, and deposits of crushed material mask the primary relief forms to a lesser extent. The secondary craters themselves are deeper than the lunar ones, which is again explained by the fact that the fragments falling to the surface experience greater acceleration due to gravity.

Just as on the Moon, depending on the relief, one can distinguish predominant uneven “continental” and much smoother “sea” areas. The latter are predominantly hollows, which, however, are significantly smaller than on the Moon; their sizes usually do not exceed 400-600 km. In addition, some basins are poorly distinguishable against the background of the surrounding terrain. The exception is the mentioned vast basin Canoris (Sea of Heat), about 1300 km long, reminiscent of the famous Sea of Rains on the Moon.

In the predominant continental part of the surface of Mercury, one can distinguish both heavily cratered areas, with the greatest degree of degradation of craters, and old intercrater plateaus occupying vast territories, indicating widespread ancient volcanism. These are the most ancient preserved landforms on the planet. The leveled surfaces of the basins are obviously covered with the thickest layer of crushed rocks - regolith. Along with a small number of craters, there are folded ridges reminiscent of the moon. Some of the flat areas adjacent to the basins were probably formed by the deposition of material ejected from them. At the same time, for most of the plains, definite evidence of their volcanic origin has been found, but this is volcanism of a later date than on the intercrater plateaus. A careful study reveals another interesting feature that sheds light on the history of the formation of the planet. We are talking about characteristic traces of tectonic activity on a global scale in the form of specific steep ledges, or scarps. The scarps range in length from 20-500 km and slope heights from several hundred meters to 1-2 km. In their morphology and geometry of location on the surface, they differ from the usual tectonic ruptures and faults observed on the Moon and Mars, and were rather formed due to thrusts, layers due to stress in the surface layer that arose during the compression of Mercury. This is evidenced by the horizontal displacement of the ridges of some craters.

Some of the scarps were bombed and partially destroyed. This means that they formed earlier than the craters on their surface. Based on the narrowing of the erosion of these craters, we can come to the conclusion that compression of the crust occurred during the formation of the “seas” about 4 billion years ago. The most likely reason for the compression should apparently be considered the beginning of the cooling of Mercury. According to another interesting assumption put forward by a number of experts, an alternative mechanism for the powerful tectonic activity of the planet during this period could be a tidal slowdown of the planet’s rotation by about 175 times: from the initially assumed value of about 8 hours to 58.6 days.

Venus.

General information.

Venus is the second closest planet to the Sun, almost the same size as Earth, and its mass is more than 80% of Earth's mass. For these reasons, Venus is sometimes called Earth's twin or sister. However, the surface and atmosphere of these two planets are completely different. On Earth there are rivers, lakes, oceans and the atmosphere that we breathe. Venus is a searingly hot planet with a thick atmosphere that would be fatal to humans. The average distance from Venus to the Sun is 108.2 million km; it is almost constant, since the orbit of Venus is closer to a circle than our planet. Venus receives more than twice as much light and heat from the Sun as Earth does. Nevertheless, on the shadow side Venus is dominated by frost of more than 20 degrees below zero, since the sun's rays do not reach here for a very long time. The planet has a very dense, deep and very cloudy atmosphere, preventing us from seeing the surface of the planet. The atmosphere (gas shell) was discovered by M.V. Lomonosov in 1761, which also showed the similarity of Venus with the Earth. The planet has no satellites.

Movement.

Venus has an almost circular orbit (eccentricity 0.007), which it travels around in 224.7 Earth days at a speed of 35 km/sec. at a distance of 108.2 million km from the Sun. Venus rotates around its axis in 243 Earth days - the longest time among all the planets. Around its axis, Venus rotates in the opposite direction, that is, in the direction opposite to its orbital movement. Such a slow, and, moreover, reverse rotation means that, when viewed from Venus, the Sun rises and sets only twice a year, since a Venusian day is equal to 117 Earth days. The rotation axis of Venus is almost perpendicular to the orbital plane (inclination 3°), so there are no seasons - one day is similar to another, has the same duration and the same weather. This weather uniformity is further enhanced by the specificity of the Venusian atmosphere - its strong greenhouse effect. Also, Venus, like the Moon, has its own phases.

Temperature.

The temperature is about 750 K over the entire surface both day and night. The reason for such a high temperature near the surface of Venus is the greenhouse effect: the sun's rays pass through the clouds of its atmosphere relatively easily and heat the surface of the planet, but the thermal infrared radiation of the surface itself exits through the atmosphere back into space with great difficulty. On Earth, where the amount of carbon dioxide in the atmosphere is small, the natural greenhouse effect increases global temperatures by 30°C, and on Venus it raises temperatures by another 400°C. By studying the physical consequences of the strongest greenhouse effect on Venus, we have a good idea of the results that could result from the accumulation of excess heat on Earth, caused by the growing concentration of carbon dioxide in the atmosphere due to the burning of fossil fuels - coal and oil.

In 1970, the first spacecraft to arrive on Venus could only withstand the intense heat for about one hour, but that was just long enough to send data back to Earth about conditions on the surface.

Atmosphere.

The mysterious atmosphere of Venus has been the centerpiece of a robotic exploration program over the past two decades. The most important aspects of her research were the chemical composition, vertical structure and dynamics of the air environment. Much attention was paid to cloud cover, which plays the role of an insurmountable barrier to the penetration of electromagnetic waves of the optical range into the depths of the atmosphere. During television filming of Venus, it was possible to obtain an image of only the cloud cover. The extraordinary dryness of the air and its phenomenal greenhouse effect, due to which the actual temperature of the surface and lower layers of the troposphere turned out to be more than 500 degrees higher than the effective (equilibrium) one, were incomprehensible.

The atmosphere of Venus is extremely hot and dry, due to the greenhouse effect. It is a dense blanket of carbon dioxide that retains heat coming from the Sun. As a result, a large amount of thermal energy accumulates. The pressure at the surface is 90 bar (as in the seas on Earth at a depth of 900 m). Spaceships have to be designed to withstand the crushing, crushing force of the atmosphere.

The atmosphere of Venus consists mainly of carbon dioxide (CO 2) -97%, which can act as a kind of blanket, trapping solar heat, as well as a small amount of nitrogen (N 2) -2.0%, water vapor (H 2 O) -0.05% and oxygen (O) -0.1%. Hydrochloric acid (HCl) and hydrofluoric acid (HF) were found as minor impurities. The total amount of carbon dioxide on Venus and Earth is approximately the same. Only on Earth is it bound in sedimentary rocks and partly absorbed by the water masses of the oceans, but on Venus it is all concentrated in the atmosphere. During the day, the planet's surface is illuminated by diffuse sunlight with approximately the same intensity as on a cloudy day on Earth. A lot of lightning has been seen on Venus at night.

The clouds of Venus consist of microscopic droplets of concentrated sulfuric acid (H 2 SO 4). The top layer of clouds is 90 km away from the surface, the temperature there is about 200 K; the lower layer is at 30 km, the temperature is about 430 K. Even lower it is so hot that there are no clouds. Of course, there is no liquid water on the surface of Venus. The atmosphere of Venus at the level of the upper cloud layer rotates in the same direction as the surface of the planet, but much faster, completing a revolution in 4 days; this phenomenon is called superrotation, and no explanation has yet been found for it.

Surface.

The surface of Venus is covered with hundreds of thousands of volcanoes. There are several very large ones: 3 km high and 500 km wide. But most of the volcanoes are 2-3 km across and about 100 m in height. The outpouring of lava on Venus takes much longer than on Earth. Venus is too hot for ice, rain, or storms, so there is no significant weathering. This means that volcanoes and craters have hardly changed since they were formed millions of years ago.

Venus is covered with hard rocks. Hot lava circulates underneath them, causing tension in the thin surface layer. Lava constantly erupts from holes and fractures in solid rock. In addition, volcanoes constantly emit jets of small droplets of sulfuric acid. In some places, thick lava, gradually oozing, accumulates in the form of huge puddles up to 25 km wide. In other places, huge bubbles of lava form domes on the surface, which then collapse.

On the surface of Venus, a rock rich in potassium, uranium and thorium was discovered, which in terrestrial conditions corresponds to the composition not of primary volcanic rocks, but of secondary ones that have undergone exogenous processing. In other places, the surface contains coarse crushed stone and blocky material of dark rocks with a density of 2.7-2.9 g/cm and other elements characteristic of basalts. Thus, the surface rocks of Venus turned out to be the same as those on the Moon, Mercury and Mars, erupted igneous rocks of basic composition.

Little is known about the internal structure of Venus. It probably has a metal core occupying 50% of the radius. But the planet does not have a magnetic field due to its very slow rotation.

Venus is by no means the hospitable world it was once supposed to be. With its atmosphere of carbon dioxide, clouds of sulfuric acid and terrible heat, it is completely unsuitable for humans. Under the weight of this information, some hopes collapsed: after all, less than 20 years ago, many scientists considered Venus a more promising object for space exploration than Mars.

Earth.

General information.

Earth is the third planet from the Sun in the solar system. The shape of the Earth is close to an ellipsoid, flattened at the poles and stretched in the equatorial zone. The average radius of the Earth is 6371.032 km, polar - 6356.777 km, equatorial - 6378.160 km. Weight - 5.976*1024 kg. The average density of the Earth is 5518 kg/m³. The Earth's surface area is 510.2 million km², of which approximately 70.8% is in the World Ocean. Its average depth is about 3.8 km, the maximum (Mariana Trench in the Pacific Ocean) is 11.022 km; the volume of water is 1370 million km³, the average salinity is 35 g/l. Land makes up 29.2% respectively and forms six continents and islands. It rises above sea level by an average of 875 m; highest height (peak of Chomolungma in the Himalayas) 8848 m. Mountains occupy over 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and woodlands - about 20%, forests - about 30%, glaciers - over 10%. Over 10% of the land is occupied by agricultural land.

The Earth has only one satellite - the Moon.

Thanks to its unique, perhaps unique, natural conditions in the Universe, the Earth became the place where organic life arose and developed. According to modern cosmogonic concepts, the planet formed approximately 4.6 - 4.7 billion years ago from a protoplanetary cloud captured by the gravity of the Sun. The formation of the first, most ancient of the studied rocks took 100-200 million years. About 3.5 billion years ago, conditions favorable for the emergence of life arose. Homo sapiens (Homo sapiens) as a species appeared about half a million years ago, and the formation of the modern type of man dates back to the time of the retreat of the first glacier, that is, about 40 thousand years ago.

Movement.

Like other planets, it moves around the Sun in an elliptical orbit with an eccentricity of 0.017. The distance from the Earth to the Sun at different points in the orbit is not the same. The average distance is about 149.6 million km. As our planet moves around the Sun, the plane of the Earth's equator moves parallel to itself in such a way that in some parts of the orbit the globe is inclined towards the Sun with its northern hemisphere, and in others - with its southern hemisphere. The period of revolution around the Sun is 365.256 days, with a daily rotation of 23 hours 56 minutes. The Earth's rotation axis is located at an angle of 66.5º to the plane of its movement around the Sun.

Atmosphere .

The Earth's atmosphere consists of 78% nitrogen and 21% oxygen (there are very few other gases in the atmosphere); it is the result of long evolution under the influence of geological, chemical and biological processes. It is possible that the Earth's primordial atmosphere was rich in hydrogen, which then escaped. Degassing of the subsoil filled the atmosphere with carbon dioxide and water vapor. But the steam condensed in the oceans, and the carbon dioxide became trapped in carbonate rocks. Thus, nitrogen remained in the atmosphere, and oxygen appeared gradually as a result of the life activity of the biosphere. Even 600 million years ago, the oxygen content in the air was 100 times lower than it is today.

Our planet is surrounded by a vast atmosphere. According to temperature, the composition and physical properties of the atmosphere can be divided into different layers. The troposphere is the region lying between the Earth's surface and an altitude of 11 km. This is a fairly thick and dense layer containing most of the water vapor in the air. Almost all atmospheric phenomena that directly interest the inhabitants of the Earth take place in it. The troposphere contains clouds, precipitation, etc. The layer separating the troposphere from the next atmospheric layer, the stratosphere, is called the tropopause. This is an area of very low temperatures.

The composition of the stratosphere is the same as the troposphere, but ozone is formed and concentrated in it. The ionosphere, that is, the ionized layer of air, is formed both in the troposphere and in lower layers. It reflects high frequency radio waves.

Atmospheric pressure at the ocean surface level is approximately 0.1 MPa under normal conditions. It is believed that the earth’s atmosphere has changed greatly in the process of evolution: it has become enriched with oxygen and acquired its modern composition as a result of long-term interaction with rocks and with the participation of the biosphere, i.e. plant and animal organisms. Evidence that such changes have actually occurred is, for example, coal deposits and thick layers of carbonate deposits in sedimentary rocks; they contain enormous amounts of carbon, which was previously part of the earth's atmosphere in the form of carbon dioxide and carbon monoxide. Scientists believe that the ancient atmosphere came from gaseous products of volcanic eruptions; its composition is judged by chemical analysis of gas samples “immured” in the cavities of ancient rocks. The studied samples, which are approximately 3.5 billion years old, contain approximately 60% carbon dioxide, and the remaining 40% are sulfur compounds, ammonia, hydrogen chloride and hydrogen fluoride. Nitrogen and inert gases were found in small quantities. All oxygen was chemically bound.

For biological processes on Earth, the ozonosphere is of great importance - the ozone layer located at an altitude of 12 to 50 km. The area above 50-80 km is called the ionosphere. Atoms and molecules in this layer are intensively ionized under the influence of solar radiation, in particular ultraviolet radiation. If it were not for the ozone layer, radiation flows would reach the surface of the Earth, causing destruction in the living organisms existing there. Finally, at distances of more than 1000 km, the gas is so rarefied that collisions between molecules cease to play a significant role, and the atoms are more than half ionized. At an altitude of about 1.6 and 3.7 Earth radii there are the first and second radiation belts.

The structure of the planet.

The main role in the study of the internal structure of the Earth is played by seismic methods based on the study of the propagation in its thickness of elastic waves (both longitudinal and transverse) arising during seismic events - during natural earthquakes and as a result of explosions. Based on these studies, the Earth is conventionally divided into three regions: the crust, the mantle and the core (in the center). The outer layer - the crust - has an average thickness of about 35 km. The main types of the earth's crust are continental (continental) and oceanic; In the transition zone from the continent to the ocean, an intermediate type of crust is developed. The thickness of the crust varies over a fairly wide range: the oceanic crust (taking into account the layer of water) is about 10 km thick, while the thickness of the continental crust is tens of times greater. Surface sediments occupy a layer about 2 km thick. Beneath them is a granite layer (on continents its thickness is 20 km), and below is approximately 14 km (on both continents and oceans) basalt layer (lower crust). The density at the center of the Earth is about 12.5 g/cm³. Average densities are: 2.6 g/cm3 at the Earth's surface, 2.67 g/cm3 for granite, 2.85 g/cm3 for basalt.

The Earth's mantle, also called the silicate shell, extends to a depth of approximately 35 to 2885 km. It is separated from the crust by a sharp boundary (the so-called Mohorovich boundary), deeper than which the velocities of both longitudinal and transverse elastic seismic waves, as well as the mechanical density, increase abruptly. Densities in the mantle increase with depth from approximately 3.3 to 9.7 g/cm3. Extensive lithospheric plates are located in the crust and (partially) in the mantle. Their secular movements not only determine continental drift, which significantly affects the appearance of the Earth, but also have a bearing on the location of seismic zones on the planet. Another boundary discovered by seismic methods (the Gutenberg boundary) - between the mantle and the outer core - is located at a depth of 2775 km. On it, the speed of longitudinal waves drops from 13.6 km/s (in the mantle) to 8.1 km/s (in the core), and the speed of transverse waves decreases from 7.3 km/s to zero. The latter means that the outer core is liquid. According to modern concepts, the outer core consists of sulfur (12%) and iron (88%). Finally, at depths greater than 5,120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth's mass. Presumably it is an iron-nickel alloy (80% Fe, 20% Ni).

The Earth's gravitational field is described with high accuracy by Newton's law of universal gravitation. The acceleration of gravity over the Earth's surface is determined by both gravitational and centrifugal forces due to the Earth's rotation. The acceleration of gravity at the surface of the planet is 9.8 m/sI.

The earth also has magnetic and electric fields. The magnetic field above the Earth's surface consists of a constant (or changing quite slowly) and a variable part; the latter is usually attributed to variations in the magnetic field. The main magnetic field has a structure close to dipole. The Earth's magnetic dipole moment, equal to 7.98T10^25 SGSM units, is directed approximately opposite to the mechanical one, although at present the magnetic poles are slightly shifted relative to the geographic ones. Their position, however, changes over time, and although these changes are quite slow, over geological periods of time, according to paleomagnetic data, even magnetic inversions, that is, polarity reversals, are detected. The magnetic field strengths at the north and south magnetic poles are 0.58 and 0.68 Oe, respectively, and at the geomagnetic equator - about 0.4 Oe.

The electric field above the Earth's surface has an average strength of about 100 V/m and is directed vertically downwards - this is the so-called clear weather field, but this field experiences significant (both periodic and irregular) variations.

Moon.

The Moon is the natural satellite of the Earth and the closest celestial body to us. The average distance to the Moon is 384,000 kilometers, the diameter of the Moon is about 3,476 km. The average density of the Moon is 3.347 g/cm3 or about 0.607 the average density of the Earth. The mass of the satellite is 73 trillion tons. The acceleration of gravity on the surface of the Moon is 1.623 m/sІ.

The Moon moves around the Earth at an average speed of 1.02 km/sec in a roughly elliptical orbit in the same direction in which the vast majority of other bodies in the Solar System move, that is, counterclockwise when looking at the Moon's orbit from the North Pole. The period of revolution of the Moon around the Earth, the so-called sidereal month, is equal to 27.321661 average days, but is subject to slight fluctuations and a very small secular reduction.

Not being protected by the atmosphere, the surface of the Moon heats up to +110°C during the day and cools down to -120°C at night, however, as radio observations have shown, these huge temperature fluctuations penetrate only a few decimeters deep due to the extremely weak thermal conductivity of the surface layers.

The relief of the lunar surface was mainly clarified as a result of many years of telescopic observations. The “lunar seas,” occupying about 40% of the visible surface of the Moon, are flat lowlands intersected by cracks and low winding ridges; There are relatively few large craters in the seas. Many seas are surrounded by concentric ring ridges. The remaining, lighter surface is covered with numerous craters, ring-shaped ridges, grooves, and so on.

Mars.

General information.

Mars is the fourth planet of the solar system. Mars - from the Greek "Mas" - male power - the god of war. According to its basic physical characteristics, Mars belongs to the terrestrial planets. In diameter it is almost half the size of Earth and Venus. The average distance from the Sun is 1.52 AU. The equatorial radius is 3380 km. The average density of the planet is 3950 kg/m³. Mars has two satellites - Phobos and Deimos.

Atmosphere.

The planet is shrouded in a gaseous shell - an atmosphere that has a lower density than the earth's. Even in the deep depressions of Mars, where the atmospheric pressure is greatest, it is approximately 100 times less than at the surface of the Earth, and at the level of Martian mountain peaks it is 500-1000 times less. Its composition resembles the atmosphere of Venus and contains 95.3% carbon dioxide with an admixture of 2.7% nitrogen, 1.6% argon, 0.07% carbon monoxide, 0.13% oxygen and approximately 0.03% water vapor, the content which changes, as well as admixtures of neon, krypton, xenon.

The average temperature on Mars is significantly lower than on Earth, about -40° C. Under the most favorable conditions in summer, on the daytime half of the planet, the air warms up to 20° C - a completely acceptable temperature for the inhabitants of the Earth. But on a winter night, frost can reach -125° C. Such sudden temperature changes are caused by the fact that the thin atmosphere of Mars is not able to retain heat for a long time.

Strong winds often blow over the surface of the planet, the speed of which reaches 100 m/s. Low gravity allows even thin air currents to raise huge clouds of dust. Sometimes quite large areas on Mars are covered in enormous dust storms. A global dust storm raged from September 1971 to January 1972, raising about a billion tons of dust into the atmosphere to a height of more than 10 km.

There is very little water vapor in the atmosphere of Mars, but at low pressure and temperature it is in a state close to saturation and often collects in clouds. Martian clouds are rather inexpressive compared to terrestrial ones, although they have a variety of shapes and types: cirrus, wavy, leeward (near large mountains and under the slopes of large craters, in places protected from the wind). There is often fog over lowlands, canyons, valleys, and at the bottom of craters during cold times of the day.

As shown by photographs from the American landing stations Viking 1 and Viking 2, the Martian sky in clear weather has a pinkish color, which is explained by the scattering of sunlight on dust particles and the illumination of the haze by the orange surface of the planet. In the absence of clouds, the gas shell of Mars is much more transparent than the earth’s, including for ultraviolet rays, which are dangerous for living organisms.

Seasons.

A solar day on Mars lasts 24 hours and 39 minutes. 35 s. The significant inclination of the equator to the orbital plane leads to the fact that in some parts of the orbit, predominantly the northern latitudes of Mars are illuminated and heated by the Sun, while in others - the southern ones, i.e., a change of seasons occurs. The Martian year lasts about 686.9 days. The change of seasons on Mars occurs in the same way as on Earth. Seasonal changes are most pronounced in the polar regions. In winter, the polar caps occupy a significant area. The boundary of the northern polar cap can move away from the pole by a third of the distance from the equator, and the boundary of the southern cap covers half of this distance. This difference is caused by the fact that in the northern hemisphere, winter occurs when Mars passes through the perihelion of its orbit, and in the southern hemisphere, when it passes through aphelion. Because of this, winter in the southern hemisphere is colder than in the northern hemisphere. The ellipticity of the Martian orbit leads to significant differences in the climate of the northern and southern hemispheres: in the middle latitudes, winters are colder and summers are warmer than in the southern, but shorter than in the northern. When summer begins in the northern hemisphere of Mars, the northern polar cap quickly decreases, but at this time another grows - near the south pole, where winter comes. At the end of the 19th and beginning of the 20th centuries, it was believed that the polar caps of Mars were glaciers and snow. According to modern data, both polar caps of the planet - northern and southern - consist of solid carbon dioxide, i.e. dry ice, which is formed when carbon dioxide, which is part of the Martian atmosphere, freezes, and water ice mixed with mineral dust.

The structure of the planet.

Due to its low mass, the gravity on Mars is almost three times lower than on Earth. Currently, the structure of the gravitational field of Mars has been studied in detail. It indicates a slight deviation from the uniform distribution of density on the planet. The core can have a radius of up to half the radius of the planet. Apparently, it consists of pure iron or an alloy of Fe-FeS (iron-iron sulfide) and possibly hydrogen dissolved in them. Apparently, the core of Mars is partially or completely liquid.

Mars should have a thick crust 70-100 km thick. Between the core and the crust there is a silicate mantle enriched in iron. Red iron oxides present in surface rocks determine the color of the planet. Now Mars continues to cool.

The planet's seismic activity is weak.

Surface.

The surface of Mars, at first glance, resembles the moon. However, in reality its relief is very diverse. Over the course of Mars' long geological history, its surface has been altered by volcanic eruptions and marsquakes. Deep scars on the face of the god of war were left by meteorites, wind, water and ice.

The planet's surface consists of two contrasting parts: ancient highlands covering the southern hemisphere, and younger plains concentrated in northern latitudes. In addition, two large volcanic regions stand out - Elysium and Tharsis. The difference in altitude between the mountainous and lowland areas reaches 6 km. Why different areas differ so much from each other is still unclear. Perhaps this division is associated with a very long-standing catastrophe - the fall of a large asteroid on Mars.

The high mountain part has preserved traces of active meteorite bombardment that took place about 4 billion years ago. Meteor craters cover 2/3 of the planet's surface. There are almost as many of them on the old highlands as on the Moon. But many Martian craters managed to “lose their shape” due to weathering. Some of them, apparently, were once washed away by streams of water. The northern plains look completely different. 4 billion years ago there were many meteorite craters on them, but then the catastrophic event, which has already been mentioned, erased them from 1/3 of the planet’s surface and its relief in this area began to form anew. Individual meteorites fell there later, but in general there are few impact craters in the north.

The appearance of this hemisphere was determined by volcanic activity. Some of the plains are completely covered with ancient igneous rocks. Streams of liquid lava spread over the surface, solidified, and new streams flowed along them. These petrified "rivers" are concentrated around large volcanoes. At the ends of lava tongues, structures similar to terrestrial sedimentary rocks are observed. Probably, when hot igneous masses melted layers of underground ice, fairly large bodies of water formed on the surface of Mars, which gradually dried up. The interaction of lava and underground ice also led to the appearance of numerous grooves and cracks. In low-lying areas of the northern hemisphere far from volcanoes, sand dunes extend. There are especially many of them near the northern polar cap.

The abundance of volcanic landscapes indicates that in the distant past Mars experienced a rather turbulent geological era, most likely it ended about a billion years ago. The most active processes occurred in the regions of Elysium and Tharsis. At one time, they were literally squeezed out of the bowels of Mars and now rise above its surface in the form of enormous swellings: Elysium is 5 km high, Tharsis is 10 km high. Numerous faults, cracks, and ridges are concentrated around these swellings - traces of ancient processes in the Martian crust. The most ambitious system of canyons, several kilometers deep, the Valles Marineris, begins at the top of the Tharsis Mountains and stretches 4 thousand kilometers to the east. In the central part of the valley its width reaches several hundred kilometers. In the past, when Mars' atmosphere was denser, water could flow into the canyons, creating deep lakes in them.

The volcanoes of Mars are exceptional phenomena by earthly standards. But even among them, the Olympus volcano, located in the northwest of the Tharsis Mountains, stands out. The diameter of the base of this mountain reaches 550 km, and the height is 27 km, i.e. it is three times larger than Everest, the highest peak on Earth. Olympus is crowned with a huge 60-kilometer crater. Another volcano, Alba, has been discovered east of the highest part of the Tharsis Mountains. Although it cannot rival Olympus in height, its base diameter is almost three times larger.

These volcanic cones were the result of quiet outpourings of very liquid lava, similar in composition to the lava of the terrestrial volcanoes of the Hawaiian Islands. Traces of volcanic ash on the slopes of other mountains suggest that catastrophic eruptions have sometimes occurred on Mars.

In the past, running water played a huge role in the formation of the Martian topography. At the first stages of the study, Mars seemed to astronomers to be a desert and waterless planet, but when the surface of Mars was photographed at close range, it turned out that in the old highlands there were often gullies that seemed to have been left by flowing water. Some of them look as if they were broken through by stormy, rushing streams many years ago. They sometimes stretch for many hundreds of kilometers. Some of these “streams” are quite old. Other valleys are very similar to the beds of calm earthly rivers. They probably owe their appearance to the melting of underground ice.

Some additional information about Mars can be obtained by indirect methods based on studies of its natural satellites - Phobos and Deimos.

Satellites of Mars.

The moons of Mars were discovered on August 11 and 17, 1877 during the great opposition by American astronomer Asaph Hall. The satellites received such names from Greek mythology: Phobos and Deimos - the sons of Ares (Mars) and Aphrodite (Venus), always accompanied their father. Translated from Greek, “phobos” means “fear”, and “deimos” means “horror”.

Phobos. Deimos.

Both satellites of Mars move almost exactly in the plane of the planet's equator. With the help of spacecraft, it has been established that Phobos and Deimos have an irregular shape and in their orbital position they always remain facing the planet with the same side. The dimensions of Phobos are about 27 km, and Deimos is about 15 km. The surface of Mars' moons consists of very dark minerals and is covered with numerous craters. One of them, on Phobos, has a diameter of about 5.3 km. The craters were probably created by meteorite bombardment; the origin of the system of parallel grooves is unknown. The angular velocity of Phobos's orbital motion is so high that, overtaking the axial rotation of the planet, it rises, unlike other luminaries, in the west, and sets in the east.

The search for life on Mars.

For a long time, there has been a search for forms of extraterrestrial life on Mars. When exploring the planet with Viking spacecraft, three complex biological experiments were performed: pyrolysis decomposition, gas exchange, and label decomposition. They are based on the experience of studying earthly life. The pyrolysis decomposition experiment was based on determining the processes of photosynthesis involving carbon, the tag decomposition experiment was based on the assumption that water was necessary for existence, and the gas exchange experiment took into account that Martian life must use water as a solvent. Although all three biological experiments yielded positive results, they are likely non-biological in nature and can be explained by inorganic reactions of the nutrient solution with a substance of Martian origin. So, we can summarize that Mars is a planet that does not have the conditions for the emergence of life.

Conclusion

We got acquainted with the current state of our planet and the planets of the Earth group. The future of our planet, and indeed the entire planetary system, if nothing unexpected happens, seems clear. The likelihood that the established order of planetary motion will be disrupted by some wandering star is small, even within a few billion years. In the near future, we cannot expect major changes in the flow of solar energy. It is likely that ice ages may recur. A person can change the climate, but in doing so he can make a mistake. Continents will rise and fall in subsequent eras, but we hope that the processes will occur slowly. Massive meteorite impacts are possible from time to time.

But basically the solar system will retain its modern appearance.

Plan.

1. Introduction.

2. Mercury.

3. Venus.

6. Conclusion.

7. Literature.

Planet Mercury.

Surface of Mercury.

Planet Venus.

Surface of Venus.

Planet Earth.

Ground surface.

The planet Mars.

Surface of Mars.

Volcano Olympus

The terrestrial group of planets is closest to the Sun. It consists of metal or silicate rock, which is why such a planet is called rocky or telluric. The terrestrial planet is located inside the solar system. Such a planet is called terrestrial because it contains elements reminiscent of planet Earth. And it even got its name from Latin “ Terra "- translated means "earth".

While gas giant planets are composed of various types of water, helium and hydrogen, which can be transformed into a variety of physical states, the terrestrial group of planets have an exclusively solid surface. These planets are included in the same group because of the similarity of their structure: inside they have a metallic core, which is iron, and this core is surrounded by a special silicate mantle. And also these planets are combined into one group, since each of them has terrestrial components, which include volcanoes, mountains, canyons and others.

The terrestrial group of planets has an uncompressed density equal to zero pressure of the average density of matter on any planet. But since compression in planetary cores can increase its density, the real average density and uncompressed density may differ. Scientists determine the average density for each terrestrial planet separately, because the calculation of density depends on the size and what is included in its composition.

There is no way to know how many terrestrial planets there actually were when the solar system first began to form. Perhaps they were expelled from the four planets, or merged (combined) with each other. The planetary nebula itself reorganized itself, and there were four such planets - Mars, Mercury, Venus, and of course, the Earth itself.

Features of terrestrial planets

Mars

This planet is half the Earth and the fourth from the sun. It has almost no atmosphere, only carbon dioxide, and is the coldest (from 00 degrees to minus 113C). A day on Mars is identical to that on Earth, but the year is longer - 687 days. There are no liquids on Mars; there are ice caps of gas and frozen water. Mars is famous for its volcanoes, craters and two satellites - Deimos and Phobos.

Mercury

It is closest to the Sun and the smallest in size of all four. It is slightly larger than the Moon. The surface of Mercury is littered with impact craters that have left traces on it. This happened due to the absence (or insignificant presence) of the atmosphere. The temperature on Mercury is off the charts, with a huge range from 4270 to minus 173C. This distinguishes it from other planets. The temperature range increases/decreases depending on the location towards the sun (high on the facing side, low on the non-facing side). You can turn around the sun in 88 days. This is possible due to its very close location (46 million kilometers). It is curious that the planet is very slow and one day there is equal to 59 Earth days.

Venus

This planet is almost an analogue of the Earth (density, size, structure). There is sulfuric acid present in the clouds and carbon dioxide. Although Venus is not close to the Sun, unlike Mercury, it is the hottest (4500C). Venus is famous for its retrograde rotation: west - the sun rises, east - it sets. A day on Venus is very long and consists of 243 Earth days. And a year lasts 225 days. Venus is beautiful and presents herself brightly, appearing as the Morning Star.

Earth

It is only the fifth largest in the planetary nebula of the solar system and the third from the Sun itself. Among all the planets, it is the only inhabited one. Possessing the liquid state of water, it gave birth to life. We breathe air that is only 28 percent oxygen, the rest is nitrogen and one percent argon and carbon dioxide. The habitable planet's seasons vary due to its 23-degree vertical tilt. A year is 365 days and a day is 24 hours.

What terrestrial planets do you know? List it in your head and check if you thought correctly :). Now we will tell you about them.

Planets Mercury, Venus, Earth and Mars The four sisters are so similar, but there is no complete similarity between them. Each of them developed in its own way.

The closest ones to the Sun formed in a very hot region. Under the influence of high temperatures, light gases moved to the periphery of the solar system, so the terrestrial planets consist of heavy elements such as carbon, iron, and silicon. That is, they are solid and rocky, unlike planets that formed far away and are made mostly of gas. The terrestrial planets have undergone dramatic changes since their formation. Their primary atmosphere disappeared; its replacements were light gases rising from the internal hot zones of the planets. Heavy elements moved inward and formed the core of such planets; volcanic eruptions changed their topography. The 4.5 billion years that have passed since then have changed the appearance of the planets, almost similar at the birth of such different ones today.

Mercury, a small planet close to the Sun with a very thin atmosphere, is a cratered desert scorched by the Sun. Unlike other terrestrial planets, Mercury is a planet on which nothing noteworthy happens, with the possible exception of a constant light meteor shower.

It's probably been a long time since we Venus there were oceans, well, since this planet is quite close to the Sun, the water evaporated and disappeared into space. Currently, the very dense atmosphere consists mainly of carbon dioxide. Several layers of sulfuric acid prevent the sun's rays from reaching the surface. Due to the greenhouse effect, the temperature rises to 500 degrees. The surface of the planet, hidden under the clouds, was studied using the Magellan interplanetary station in 1990. Vast plains, mountains, deep fissures, volcanoes and several meteorite craters were discovered.

Most of the surface Earth occupied by water, which remains in a liquid state due to the fact that the planet is not too close and not too far from the Sun. The atmosphere, a state of mostly nitrogen, oxygen, a small amount of carbon dioxide and water vapor, gives rise to the climate we know. Today's volcanic processes are much less significant than in the past.

U Mars Previously, there was a different, denser atmosphere that favored a mild climate, and there were laths and oceans. Well, since the planet is small, and the mass is not enough for the gravitational force to hold the gas, most of it disappeared into space. The atmosphere now consists of carbon dioxide. The temperature has dropped, the water is now frozen under a layer of soil. From the inside, Mars also cooled faster than Venus and Earth, and huge volcanoes went extinct a billion years ago. Sometimes hurricane-force winds raise clouds of dust that take weeks to settle on the surface.

Kreneva Evgeniya

The work describes the planets belonging to the Terrestrial group. The conditions on these planets, their common features, as well as the characteristics of each planet are considered.

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TERRESTRIAL PLANETS Presentation on astronomy Prepared by 11th grade student Kreneva Evgenia GBOU Secondary School No. 8, Moscow

SOLAR SYSTEM

Terrestrial Planets These are the four planets of the solar system: Mercury, Venus, Earth and Mars. They are also called inner planets, in contrast to the outer planets - the giant planets.

Terrestrial planets have a high density and consist mainly of silicates and metal, as well as oxygen, silicon, iron, magnesium, aluminum and other heavy elements. The largest terrestrial planet is Earth, but it is more than 14 times less massive than the least massive gas planet, Uranus. All terrestrial planets have the following structure: - in the center, a core made of iron with an admixture of nickel, - a mantle, consisting of silicates, - a crust, formed as a result of partial melting of the mantle and also consisting of silicate rocks, but enriched in incompatible elements. Of the terrestrial planets, Mercury does not have a crust, which is explained by its destruction as a result of meteorite bombardment.

MERCURY Is closest to the sun. The existence of this planet was mentioned in ancient Sumerian writings, which date back to the third millennium BC. This planet got its name from the Roman pantheon, Mercury, the patron saint of merchants, who also had his Greek counterpart, Hermes. Mercury completely circles the sun in eighty-eight Earth days. It travels around its axis in less than sixty days, which by Mercury standards is two-thirds of a year. The temperature on the surface of Mercury can vary greatly - from + 430 degrees on the sun side to + 180 degrees on the shadow side. In our solar system, these differences are the strongest.

MERCURY An unusual phenomenon can be observed on Mercury, which is called the Joshua effect. When the sun on Mercury reaches a certain point, it stops and begins to go in the opposite direction, and not like on Earth - it must go around a full circle around the planet. Mercury is the smallest planet of the Earth group. It is smaller in size than even the largest satellites of the planets Jupiter and Saturn. The surface of Mercury is similar to the surface of the Moon - all strewn with craters. The only difference with the lunar surface is that Mercury has numerous oblique, jagged slopes that can extend for many hundreds of kilometers. These slopes were formed as a result of compression as the planet cooled.

MERCURY One of the most popular and visible parts of the planet is the so-called Heat Plain. This is a crater that gets its name due to its close location to the "hot longitudes". The crater has a diameter of one thousand three hundred kilometers. Most likely, the celestial body that made this crater in ancient times had a diameter of at least one hundred kilometers. Thanks to gravity, Mercury also captures particles of the solar wind, which in turn create a rather thin atmosphere around Mercury. Moreover, they are replaced every two hundred days. In addition, this planet is the fastest planet in our system. The average speed of its rotation around the sun is about forty-seven and a half kilometers per second, which is twice as fast as the Earth.

VENUS The atmosphere of Venus is quite aggressive, because relative to the Earth it has a very high temperature and there are poisonous clouds in the sky. The atmosphere of Venus consists mainly of carbon dioxide. If you find yourself in the atmosphere of this planet, you will experience a pressure of about eighty-five kg per 1 square centimeter. In the Earth's atmosphere the pressure will be eighty-five times less. If you throw a coin in the atmosphere of Venus, it will fall as if in a layer of water. Thus, walking on the surface of this planet is just as difficult as walking on the bottom of the ocean. And if, God forbid, the wind rises on Venus, it will carry you like a sea wave carries a sliver.

VENUS The atmosphere of this planet is 96% carbon dioxide. This is what creates the greenhouse effect. The planet's surface is heated by the sun, and the resulting heat cannot be dissipated into space because it is reflected by a layer of carbon dioxide. That's why the temperature of this planet is about four hundred and eighty degrees, like an oven.

VENUS The surface of Venus is dotted with thousands of volcanoes. Science fiction writers described Venus as similar to Earth. It was believed that Venus was shrouded in clouds. This means that the surface of this planet should be dotted with swamps. This means that it probably has a very rainy climate, which leads to a lot of cloudiness and a lot of humidity. In reality, everything is completely different - in the early seventies, the union sent spaceships to the surface of Venus, which clarified the situation. It turned out that the surface of this planet is made up of continuous rocky deserts, where there is absolutely no water. Of course, at such a high temperature there could never be any water.

EARTH Earth ranks fifth in size and mass among the large planets, but among the terrestrial planets, it is the largest. Its most important difference from other planets in the solar system is the existence of life on it, which reached its highest, intelligent form with the advent of man. According to modern cosmogonic concepts, the Earth was formed ~4.5 billion years ago by gravitational condensation from gas and dust matter scattered in the circumsolar space, containing all the chemical elements known in nature.

EARTH The formation of the Earth was accompanied by differentiation of matter, which was facilitated by the gradual heating of the earth's interior, mainly due to the heat released during the decay of radioactive elements (uranium, thorium, potassium, etc.). The result of this differentiation was the division of the Earth into concentrically located layers - the geosphere, differing in chemical composition, state of aggregation and physical properties. The Earth's core formed in the center, surrounded by a mantle. From the lightest and most fusible components of the substance released from the mantle during melting processes, the earth's crust located above the mantle arose. The collection of these internal geospheres, bounded by the solid earth's surface, is sometimes called the "solid" Earth.

EARTH “Solid” Earth contains almost the entire mass of the planet. Beyond its boundaries are the external geospheres - water (hydrosphere) and air (atmosphere), which were formed from vapors and gases released from the bowels of the Earth during degassing of the mantle. The differentiation of the substance of the Earth's mantle and the replenishment of the products of differentiation of the earth's crust, water and air shells occurred throughout geological history and continues to this day.

MARS This planet is named after the famous god of War in Rome, because the color of this planet is very reminiscent of the color of blood. This planet is also called the “red planet”. It is believed that this color of the planet is associated with iron oxide, which is present in the atmosphere of Mars. Mars is the seventh largest planet in the solar system. It is considered to be the home of the Valles Marineris - a canyon that is much longer and deeper than the famous Grand Canyon in the USA. By the way, there are quite a few mountains on Mars, and the height of these mountains is sometimes much higher than our Everest. Here, by the way, there is also Olympus - the highest and most famous mountain in the entire solar system.

MARS Mars has the largest volcanoes in the solar system. But the atmosphere of this planet is one hundred times less dense than Earth’s. But this is enough to maintain the weather system on the planet - that means wind and clouds. Mars boasts an average temperature of minus sixty degrees. A year on Mars = 687 Earth days. But a day on Mars is as close as possible to a day on Earth - it is 24 hours, 39 minutes. and 35 sec. Mars has a very thick crust - about fifty kilometers in cross section. Mars also has two moons - Deimos and Phobos.

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Introduction

The terrestrial planets include the planets: Mercury, Venus, Earth and Mars.

Mercury.

General information.

Movement.

Atmosphere.

The pressure at the surface of the planet is approximately 500 billion times less than at the surface of the Earth.

Temperature.

Surface.

Venus.

General information.

Movement.

Temperature.

In 1970, the first spacecraft to arrive on Venus could only withstand the intense heat for about one hour, but that was just long enough to send data back to Earth about conditions on the surface.

Atmosphere.

Surface.

Little is known about the internal structure of Venus. It probably has a metal core occupying 50% of the radius. But the planet does not have a magnetic field due to its very slow rotation.

Earth.

General information.

Earth is the third planet from the Sun in the solar system. The shape of the Earth is close to an ellipsoid, flattened at the poles and stretched in the equatorial zone. The average radius of the Earth is 6371.032 km, polar - 6356.777 km, equatorial - 6378.160 km. Weight - 5.976*1024 kg. The average density of the Earth is 5518 kg/m³. The Earth's surface area is 510.2 million km², of which approximately 70.8% is in the World Ocean. Its average depth is about 3.8 km, the maximum (Mariana Trench in the Pacific Ocean) is 11.022 km; water volume is 1370 million km³, average salinity is 35 g/l. Land makes up 29.2% respectively and forms six continents and islands. It rises above sea level by an average of 875 m; highest height (peak of Chomolungma in the Himalayas) 8848 m. Mountains occupy over 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and woodlands - about 20%, forests - about 30%, glaciers - over 10%. Over 10% of the land is occupied by agricultural land.

The Earth has only one satellite - the Moon.

Thanks to its unique, perhaps unique, natural conditions in the Universe, the Earth became the place where organic life arose and developed. By According to modern cosmogonic ideas, the planet formed approximately 4.6 - 4.7 billion years ago from a protoplanetary cloud captured by the gravity of the Sun. The formation of the first, most ancient of the studied rocks took 100-200 million years. About 3.5 billion years ago, conditions favorable for the emergence of life arose. Homo sapiens (Homo sapiens) as a species appeared about half a million years ago, and the formation of the modern type of man dates back to the time of the retreat of the first glacier, that is, about 40 thousand years ago.

Movement.

Atmosphere .

The structure of the planet.

The main role in the study of the internal structure of the Earth is played by seismic methods based on the study of the propagation in its thickness of elastic waves (both longitudinal and transverse) arising during seismic events - during natural earthquakes and as a result of explosions. Based on these studies, the Earth is conventionally divided into three regions: the crust, the mantle and the core (in the center). The outer layer - the crust - has an average thickness of about 35 km. The main types of the earth's crust are continental (continental) and oceanic; In the transition zone from the continent to the ocean, an intermediate type of crust is developed. The thickness of the crust varies over a fairly wide range: the oceanic crust (taking into account the layer of water) is about 10 km thick, while the thickness of the continental crust is tens of times greater. Surface sediments occupy a layer about 2 km thick. Beneath them is a granite layer (on continents its thickness is 20 km), and below is approximately 14 km (on both continents and oceans) basalt layer (lower crust). The density at the center of the Earth is about 12.5 g/cm³. Average densities are: 2.6 g/cm³ - at the Earth's surface, 2.67 g/cm³ - for granite, 2.85 g/cm³ - for basalt.

The Earth's mantle, also called the silicate shell, extends to a depth of approximately 35 to 2885 km. It is separated from the crust by a sharp boundary (the so-called Mohorovich boundary), deeper than which the velocities of both longitudinal and transverse elastic seismic waves, as well as the mechanical density, increase abruptly. Densities in the mantle increase with depth from approximately 3.3 to 9.7 g/cm³. Extensive lithospheric plates are located in the crust and (partially) in the mantle. Their secular movements not only determine continental drift, which significantly affects the appearance of the Earth, but also have a bearing on the location of seismic zones on the planet. Another boundary discovered by seismic methods (the Gutenberg boundary) - between the mantle and the outer core - is located at a depth of 2775 km. On it, the speed of longitudinal waves drops from 13.6 km/s (in the mantle) to 8.1 km/s (in the core), and the speed of transverse waves decreases from 7.3 km/s to zero. The latter means that the outer core is liquid. According to modern concepts, the outer core consists of sulfur (12%) and iron (88%). Finally, at depths greater than 5,120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth's mass. Presumably it is an iron-nickel alloy (80% Fe, 20% Ni).

Moon.

The Moon is the natural satellite of the Earth and the closest celestial body to us. The average distance to the Moon is 384,000 kilometers, the diameter of the Moon is about 3,476 km. The average density of the Moon is 3.347 g/cm³, or about 0.607 the average density of the Earth. The mass of the satellite is 73 trillion tons. The acceleration of gravity on the surface of the Moon is 1.623 m/s².