Among the terrestrial planets. Terrestrial planets

What planets terrestrial group 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.

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, within 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 - scorching hot planet with a dense 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 from the Sun more light and warmer than the Earth. 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). Upper layer the clouds are 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; 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. 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 rather thick and dense layer containing most 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. Main types earth's crust- continental (mainland) 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. It's almost double in diameter smaller than 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 Earth’s surface, and at the level of Martian mountain peaks- 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. 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. 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 nature. 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 inner region of the Solar System is inhabited by a variety of bodies: major planets, their satellites, as well as small bodies - asteroids and comets. Since 2006, a new subgroup has been introduced into the group of planets - dwarf planets, which have the internal qualities of planets (spheroidal shape, geological activity), but due to their low mass are not able to dominate in the vicinity of their orbit. Now the 8 most massive planets - from Mercury to Neptune - have been decided to be called simply planets, although in conversation astronomers, for the sake of clarity, often call them “major planets” to distinguish them from dwarf planets. The term " minor planet", which has been applied to asteroids for many years, is now recommended not to be used to avoid confusion with dwarf planets

In area major planets we see a clear division into two groups of 4 planets each: the outer part of this region is occupied by giant planets, and the inner part is occupied by much less massive terrestrial planets. The group of giants is also usually divided in half: gas giants(Jupiter and Saturn) and ice giants (Uranus and Neptune). In the group of terrestrial planets, a division in half is also emerging: Venus and Earth are extremely similar to each other in many physical parameters, and Mercury and Mars are an order of magnitude inferior to them in mass and are almost devoid of an atmosphere (even Mars has an atmosphere hundreds of times smaller than Earth’s, and Mercury is practically absent).

It should be noted that among the two hundred satellites of the planets, at least 16 bodies can be distinguished that have the internal properties of full-fledged planets. They often exceed dwarf planets in size and mass, but at the same time they are controlled by the gravity of much more massive bodies. We are talking about the Moon, Titan, the Galilean satellites of Jupiter and the like. Therefore, it would be natural to introduce into the nomenclature of the Solar System new group for such “subordinate” objects of the planetary type, calling them “satellite planets”. But this idea is currently under discussion.

Let's return to terrestrial planets. Compared to giants, they are attractive because they have a solid surface on which space probes can land. Since the 1970s, automatic stations and self-propelled vehicles of the USSR and the USA have repeatedly landed and successfully operated on the surface of Venus and Mars. There have been no landings on Mercury yet, since flights to the vicinity of the Sun and landing on a massive atmosphereless body are associated with major technical problems.

While studying terrestrial planets, astronomers do not forget the Earth itself. Analysis of images from space has made it possible to understand a lot about the dynamics of the earth’s atmosphere and its structure. upper layers(where planes and even balloons do not rise), in the processes occurring in its magnetosphere. By comparing the structure of the atmospheres of Earth-like planets, much can be understood about their history and more accurately predict their future. And since everything higher plants and animals live on the surface of our (or not only our?) planet, then the characteristics of the lower layers of the atmosphere are especially important for us. This lecture is dedicated to terrestrial planets; mainly – their appearance and conditions on the surface.

The brightness of the planet. Albedo

Looking at the planet from afar, we can easily distinguish between bodies with and without an atmosphere. The presence of an atmosphere, or more precisely, the presence of clouds in it, makes the appearance of the planet changeable and significantly increases the brightness of its disk. This is clearly visible if we arrange the planets in a row from completely cloudless (without atmosphere) to completely covered by clouds: Mercury, Mars, Earth, Venus. Rocky, atmosphereless bodies are similar to each other to the point of almost complete indistinguishability: compare, for example, large-scale photographs of the Moon and Mercury. Even an experienced eye has difficulty distinguishing between the surfaces of these dark bodies, densely covered with meteorite craters. But the atmosphere gives any planet a unique appearance.

The presence or absence of an atmosphere on a planet is controlled by three factors: temperature and gravitational potential at the surface, as well as the global magnetic field. Only the Earth has such a field, and it significantly protects our atmosphere from solar plasma flows. The Moon lost its atmosphere (if it had one at all) due to the low critical speed at the surface, and Mercury - due to high temperatures and powerful solar wind. Mars, with almost the same gravity as Mercury, was able to retain the remnants of the atmosphere, since due to its distance from the Sun it is cold and not so intensely blown by the solar wind.

In terms of their physical parameters, Venus and Earth are almost twins. They have very similar size, mass, and therefore average density. Their internal structure should also be similar - crust, mantle, iron core - although there is no certainty about this yet, since seismic and other geological data on the bowels of Venus are missing. Of course, we did not penetrate deeply into the bowels of the Earth: in most places 3-4 km, in some places 7-9 km, and only in one place 12 km. This is less than 0.2% of the Earth's radius. But seismic, gravimetric and other measurements make it possible to judge the Earth’s interior in great detail, while for other planets there is almost no such data. Detailed gravitational field maps have been obtained only for the Moon; heat flows from the interior have been measured only on the Moon; Seismometers have so far only worked on the Moon and (not very sensitive) on Mars.

Geologists still judge the internal life of planets by the features of their solid surface. For example, the absence of signs of lithospheric plates on Venus significantly distinguishes it from the Earth, in the evolution of the surface of which tectonic processes (continental drift, spreading, subduction, etc.) play a decisive role. At the same time, some indirect evidence points to the possibility of plate tectonics on Mars in the past, as well as ice field tectonics on Europa, a moon of Jupiter. Thus, the external similarity of the planets (Venus - Earth) does not guarantee the similarity of their internal structure and the processes occurring in their depths. And planets that are not similar to each other can demonstrate similar geological phenomena.

Let's return to what is available to astronomers and other specialists for direct study, namely, the surface of planets or their cloud layer. In principle, the opacity of the atmosphere in the optical range is not an insurmountable obstacle to studying the solid surface of the planet. Radar from the Earth and from space probes made it possible to study the surfaces of Venus and Titan through their atmospheres opaque to light. However, these works are sporadic, and systematic studies of planets are still carried out with optical instruments. And more importantly, optical radiation from the Sun serves as the main source of energy for most planets. Therefore, the ability of the atmosphere to reflect, scatter and absorb this radiation directly affects the climate at the surface of the planet.

The brightest luminary in the night sky, not counting the Moon, is Venus. It is very bright not only because of its relative proximity to the Sun, but also because of the dense cloud layer of concentrated sulfuric acid droplets, which perfectly reflects light. Our Earth is also not too dark, since 30-40% of the Earth's atmosphere is filled with water clouds, and they also scatter and reflect light well. Here is a photograph (pic. above) where the Earth and the Moon were simultaneously included in the frame. This photo was taken by the Galileo space probe as it flew past Earth on its way to Jupiter. Look how much darker the Moon is than the Earth and generally darker than any planet with an atmosphere. This is a general pattern - atmosphereless bodies are very dark. The fact is that under the influence of cosmic radiation, any solid substance gradually darkens.

The statement that the surface of the Moon is dark usually causes confusion: at first glance, the lunar disk appears very bright; on a cloudless night it even blinds us. But this is only in contrast to the even darker night sky. To characterize the reflectivity of any body, a quantity called albedo is used. This is the degree of whiteness, that is, the coefficient of light reflection. Albedo equal to zero - absolute blackness, complete absorption of light. An albedo equal to one is total reflection. Physicists and astronomers have several different approaches to determining albedo. It is clear that the brightness of an illuminated surface depends not only on the type of material, but also on its structure and orientation relative to the light source and the observer. For example, fluffy snow that has just fallen has one reflectance value, but snow that you stepped on with your boot will have a completely different value. And the dependence on orientation can easily be demonstrated with a mirror, letting in sunbeams.

The entire range of possible albedo values ​​is covered by known space objects. Here is the Earth reflecting about 30% of the sun's rays, mostly due to clouds. And the continuous cloud cover of Venus reflects 77% of the light. Our Moon is one of the darkest bodies, reflecting on average about 11% of light; and its visible hemisphere, due to the presence of vast dark “seas,” reflects light even worse - less than 7%. But there are also even darker objects; for example, asteroid 253 Matilda with its albedo of 4%. On the other hand, there are surprisingly bright bodies: Saturn’s moon Enceladus reflects 81% of visible light, and its geometric albedo is simply fantastic - 138%, i.e. it is brighter than a perfectly white disk of the same cross-section. It's even difficult to understand how he manages to do this. Pure snow on Earth reflects light even worse; What kind of snow lies on the surface of this small and cute Enceladus?

Heat balance

The temperature of any body is determined by the balance between the influx of heat to it and its loss. There are three known mechanisms of heat exchange: radiation, conduction and convection. The last two of them require direct contact with the environment, therefore, in the vacuum of space, the first mechanism, radiation, becomes the most important and, in fact, the only one. This creates considerable problems for space technology designers. They have to take into account several heat sources: the Sun, the planet (especially in low orbits) and the internal components of the spacecraft itself. And there is only one way to release heat - radiation from the surface of the device. To maintain the balance of heat flows, space technology designers regulate the effective albedo of the device using screen-vacuum insulation and radiators. When such a system fails, conditions in a spacecraft can become quite uncomfortable, as the story of the Apollo 13 mission to the Moon reminds us.

But for the first time this problem was encountered in the first third of the 20th century by the creators of high-altitude balloons - the so-called stratospheric balloons. In those years they did not yet know how to create complex systems thermal regulation of the sealed nacelle, therefore, they were limited to simply selecting the albedo of its outer surface. How sensitive a body's temperature is to its albedo is revealed by the history of the first flights into the stratosphere.

Gondola of your stratospheric balloon FNRS-1 Swiss Auguste Picard painted it white on one side and black on the other. The idea was that the temperature in the gondola could be regulated by turning the sphere one way or the other towards the Sun. For rotation, a propeller was installed outside. But the device did not work, the sun was shining from the “black” side and the internal temperature on the first flight rose to 38 °C. On the next flight, the entire capsule was simply covered with silver to reflect the sun's rays. It became -16 °C inside.

American stratospheric balloon designers Explorer They took Picard's experience into account and adopted a compromise option: they painted the upper part of the capsule white and the lower part black. The idea was that the upper half of the sphere would reflect solar radiation, and the lower half would absorb heat from the Earth. This option turned out to be good, but also not ideal: during the flights in the capsule it was 5 °C.

Soviet stratonauts simply insulated the aluminum capsules with a layer of felt. As practice has shown, this decision was the most successful. Internal heat, mainly generated by the crew, was sufficient to maintain a stable temperature.

But if the planet does not have its own powerful heat sources, then the albedo value is very important for its climate. For example, our planet absorbs 70% of the sunlight falling on it, processing it into its own infrared radiation, supporting the water cycle in nature, storing it as a result of photosynthesis in biomass, oil, coal, and gas. The moon absorbs almost all of the sunlight, mediocrely turning it into high-entropy infrared radiation and thereby maintaining its rather high temperature. But Enceladus, with its perfectly white surface, proudly repels almost all sunlight, for which it pays with a monstrously low surface temperature: on average about –200 °C, and in some places up to –240 °C. However, this satellite - “all in white” - does not suffer much from the external cold, since it has an alternative source of energy - the tidal gravitational influence of its neighbor Saturn (), which maintains its subglacial ocean in a liquid state. But the terrestrial planets have very weak internal heat sources, so the temperature of their solid surface largely depends on the properties of the atmosphere - on its ability, on the one hand, to reflect part of the sun's rays back into space, and on the other, to retain the energy of radiation passing through atmosphere to the surface of the planet.

Greenhouse effect and planetary climate

Depending on how far the planet is from the Sun and what proportion of sunlight it absorbs, temperature conditions on the surface of the planet and its climate are formed. What does the spectrum of any self-luminous body, such as a star, look like? In most cases, the spectrum of a star is a “single-humped”, almost Planck, curve, in which the position of the maximum depends on the temperature of the star’s surface. Unlike a star, the planet’s spectrum has two “humps”: it reflects part of the starlight in the optical range, and the other part absorbs and re-radiates in the infrared range. The relative area under these two humps is precisely determined by the degree of light reflection, that is, albedo.

Let's look at the two planets closest to us - Mercury and Venus. At first glance, the situation is paradoxical. Venus reflects almost 80% of sunlight and absorbs only about 20%. But Mercury reflects almost nothing, but absorbs everything. In addition, Venus is further from the Sun than Mercury; 3.4 times less sunlight falls per unit of its cloud surface. Taking into account differences in albedo, each square meter of Mercury's solid surface receives almost 16 times more solar heat than the same surface on Venus. And yet, on the entire solid surface of Venus there are hellish conditions - enormous temperatures (tin and lead melt!), and Mercury is cooler! At the poles there is generally Antarctica, and at the equator the average temperature is 67 °C. Of course, during the day the surface of Mercury heats up to 430 °C, and at night it cools down to –170 °C. But already at a depth of 1.5-2 meters, daily fluctuations are smoothed out, and we can talk about an average surface temperature of 67 °C. It’s hot, of course, but you can live. And in the middle latitudes of Mercury there is generally room temperature.

What's the matter? Why is Mercury, which is close to the Sun and readily absorbs its rays, heated to room temperature, while Venus, which is farther from the Sun and actively reflects its rays, is heated like a furnace? How will physics explain this?

The Earth's atmosphere is almost transparent: it transmits 80% of incoming sunlight. The air cannot escape into space as a result of convection - the planet does not let it go. This means that it can only cool in the form of infrared radiation. And if IR radiation remains locked, then it heats those layers of the atmosphere that do not release it. These layers themselves become a source of heat and partially direct it back to the surface. Some of the radiation goes into space, but the bulk of it returns to the surface of the Earth and heats it until thermodynamic equilibrium is established. How is it installed?

The temperature rises, and the maximum in the spectrum shifts (Wien’s law) until it finds a “transparency window” in the atmosphere, through which IR rays will escape into space. The balance of heat flows is established, but at a higher temperature than it would be in the absence of an atmosphere. This is the greenhouse effect.

In our lives, we quite often encounter the greenhouse effect. And not only in the form of a garden greenhouse or a pan placed on the stove, which we cover with a lid to reduce heat transfer and speed up boiling. These examples do not demonstrate a pure greenhouse effect, since both radiative and convective heat removal are reduced in them. Much closer to the described effect is the example of a clear frosty night. When the air is dry and the sky is cloudless (for example, in a desert), after sunset the earth quickly cools, and moist air and clouds smooth out daily temperature fluctuations. Unfortunately, this effect is well known to astronomers: clear starry nights can be especially cold, which makes working at the telescope very uncomfortable. Returning to the figure above, we will see the reason: it is water vapor in the atmosphere that serves as the main obstacle to heat-carrying infrared radiation.

The Moon has no atmosphere, which means there is no greenhouse effect. On its surface, thermodynamic equilibrium is established explicitly; there is no exchange of radiation between the atmosphere and the solid surface. Mars has a thin atmosphere, but its greenhouse effect still adds 8 °C. And it adds almost 40 °C to the Earth. If our planet did not have such a dense atmosphere, the Earth's temperature would be 40 °C lower. Today it averages 15 °C around the globe, but it would be –25 °C. All the oceans would freeze, the surface of the Earth would turn white with snow, the albedo would increase, and the temperature would drop even lower. In general - a terrible thing! But it’s good that the greenhouse effect in our atmosphere works and warms us. And it works even more strongly on Venus - it raises the average Venusian temperature by more than 500 degrees.

Surface of planets

Until now, we have not begun a detailed study of other planets, mainly limiting ourselves to observing their surface. How important is information about the appearance of the planet for science? What valuable information can an image of its surface tell us? If it is a gas planet, like Saturn or Jupiter, or solid, but covered with a dense layer of clouds, like Venus, then we see only the upper cloud layer, therefore, we have almost no information about the planet itself. The cloudy atmosphere, as geologists say, is a super-young surface - today it is like this, but tomorrow it will be different, or not tomorrow, but in 1000 years, which is only a moment in the life of the planet.

The Great Red Spot on Jupiter or two planetary cyclones on Venus have been observed for 300 years, but tell us only some of the general properties of the modern dynamics of their atmospheres. Our descendants, looking at these planets, will see a completely different picture, and we will never know what picture our ancestors could have seen. Thus, looking from the outside at planets with dense atmospheres, we cannot judge their past, since we see only a changeable cloud layer. A completely different matter is the Moon or Mercury, the surfaces of which contain traces of meteorite bombardments and geological processes that have occurred over the past billions of years.

And such bombardments of giant planets leave virtually no traces. One of these events occurred at the end of the twentieth century right before the eyes of astronomers. We are talking about Comet Shoemaker-Levy 9. In 1993, a strange chain of two dozen small comets. The calculation showed that these are fragments of one comet that flew near Jupiter in 1992 and was torn apart by the tidal effect of its powerful gravitational field. Astronomers did not see the actual episode of the comet’s disintegration, but only caught the moment when the chain of cometary fragments moved away from Jupiter like a “locomotive.” If the disintegration had not occurred, then the comet, having approached Jupiter along a hyperbolic trajectory, would have gone into the distance along the second branch of the hyperbola and, most likely, would never have approached Jupiter again. But the comet’s body could not withstand the tidal stress and collapsed, and the energy expended on deformation and rupture of the comet’s body reduced the kinetic energy of its orbital motion, transferring the fragments from a hyperbolic orbit to an elliptical one, closed around Jupiter. The orbital distance at the pericenter turned out to be less than the radius of Jupiter, and the fragments crashed into the planet one after another in 1994.

The incident was huge. Each “shard” of the cometary nucleus is an ice block measuring 1×1.5 km. They took turns flying into the atmosphere of the giant planet at a speed of 60 km/s (the second escape velocity for Jupiter), having a specific kinetic energy of (60/11) 2 = 30 times greater than if it were a collision with the Earth. Astronomers watched with great interest the cosmic catastrophe on Jupiter from the safety of Earth. Unfortunately, fragments of the comet hit Jupiter from the side that was not visible from Earth at that moment. Fortunately, just at that time the Galileo space probe was on its way to Jupiter; it saw these episodes and showed them to us. Due to the rapid daily rotation of Jupiter, the collision regions within a few hours became accessible to both ground-based telescopes and, what is especially valuable, near-Earth telescopes, such as the Hubble Space Telescope. This was very useful, since each block, crashing into the atmosphere of Jupiter, caused a colossal explosion, destroying the upper cloud layer and creating a window of visibility deep into the Jovian atmosphere for some time. So, thanks to the comet bombardment, we were able to look there for a short time. But 2 months passed and no traces remained on the cloudy surface: the clouds covered all the windows, as if nothing had happened.

Another thing - Earth. On our planet, meteorite scars remain for a long time. Here is the most popular meteorite crater with a diameter of about 1 km and an age of about 50 thousand years. It is still clearly visible. But craters formed more than 200 million years ago can only be found using subtle geological techniques. They are not visible from above.

By the way, there is a fairly reliable relationship between the size of a large meteorite that fell to Earth and the diameter of the crater it formed - 1:20. A kilometer-diameter crater in Arizona was formed by the impact of a small asteroid with a diameter of about 50 m. And in ancient times, larger “projectiles” - both kilometer and even ten kilometers - hit the Earth. We know today about 200 large craters; they are called astroblemes (celestial wounds); and several new ones are discovered every year. The largest, with a diameter of 300 km, was found in southern Africa, its age is about 2 billion years. In Russia, the largest crater is Popigai in Yakutia with a diameter of 100 km. Surely there are larger ones, for example, on the bottom of the oceans, where they are more difficult to notice. True, the ocean floor is geologically younger than the continents, but it seems that in Antarctica there is a crater with a diameter of 500 km. It is underwater and its presence is indicated only by the profile of the bottom.

On a surface Moon, where there is no wind or rain, where there are no tectonic processes, meteorite craters persist for billions of years. Looking at the Moon through a telescope, we read the history of cosmic bombardment. On the reverse side is an even more useful picture for science. It seems that for some reason particularly large bodies never fell there, or, when falling, they could not break through the lunar crust, which on the back side is twice as thick as on the visible side. Therefore, the flowing lava did not fill large craters and did not hide historical details. On any patch of the lunar surface there is a meteorite crater, large or small, and there are so many of them that younger ones destroy those that formed earlier. Saturation has occurred: the Moon can no longer become more cratenated than it already is. There are craters everywhere. And this is a wonderful chronicle of the history of the solar system. Based on it, several episodes of active crater formation have been identified, including the era of heavy meteorite bombardment (4.1-3.8 billion years ago), which left traces on the surface of all terrestrial planets and many satellites. Why streams of meteorites fell on the planets in that era, we still have to understand. New data are needed on the structure of the lunar interior and the composition of matter at different depths, and not just on the surface from which samples have been collected so far.

Mercury outwardly similar to the Moon, because, like it, it is devoid of an atmosphere. Its rocky surface, not subject to gas and water erosion, retains traces of meteorite bombardment for a long time. Among the terrestrial planets, Mercury contains the oldest geological traces, dating back about 4 billion years. But there is no Mercury on the surface large seas, filled with dark solidified lava and similar to lunar seas, although there are no fewer large impact craters there than on the Moon.

Mercury is about one and a half times the size of the Moon, but its mass is 4.5 times greater than the Moon. The fact is that the Moon is almost entirely rocky, while Mercury has a huge metallic core, apparently consisting mainly of iron and nickel. The radius of its metallic core is about 75% of the planet's radius (and Earth's is only 55%). The volume of Mercury's metallic core is 45% of the planet's volume (and Earth's is only 17%). Therefore, the average density of Mercury (5.4 g/cm3) is almost equal to the average density of the Earth (5.5 g/cm3) and significantly exceeds the average density of the Moon (3.3 g/cm3). Having a large metallic core, Mercury could surpass the Earth in its average density if not for the low gravity on its surface. Having a mass of only 5.5% of the Earth's, it has almost three times less gravity, which is not able to compact its interior as much as the interior of the Earth, where even the silicate mantle has a density of about (5 g/cm3), has compacted.

Mercury is difficult to study because it moves close to the Sun. To launch an interplanetary apparatus from the Earth towards it, it must be strongly slowed down, that is, accelerated in the direction opposite to the orbital motion of the Earth; only then will it begin to “fall” towards the Sun. It is impossible to do this immediately using a rocket. Therefore, in the two flights to Mercury carried out so far, gravitational maneuvers in the field of the Earth, Venus and Mercury itself were used to decelerate the space probe and transfer it to Mercury's orbit.

Mariner 10 (NASA) first went to Mercury in 1973. It first approached Venus, slowed down in its gravitational field, and then passed close to Mercury three times in 1974-75. Since all three encounters took place in the same region of the planet's orbit, and its daily rotation is synchronized with the orbital one, all three times the probe photographed the same hemisphere of Mercury, illuminated by the Sun.

There were no flights to Mercury for the next few decades. And only in 2004 was it possible to launch the second device - MESSENGER ( Mercury Surface, Space Environment, Geochemistry, and Ranging; NASA). Having carried out several gravitational maneuvers near the Earth, Venus (twice) and Mercury (three times), the probe entered orbit around Mercury in 2011 and conducted research of the planet for 4 years.

Working near Mercury is complicated by the fact that the planet is on average 2.6 times closer to the Sun than the Earth, so the flow of solar rays there is almost 7 times greater. Without a special “solar umbrella,” the probe’s electronics would overheat. The third expedition to Mercury, called BepiColombo, Europeans and Japanese take part in it. The launch is scheduled for autumn 2018. Two probes will fly at once, which will enter orbit around Mercury at the end of 2025 after flying near Earth, two near Venus and six near Mercury. In addition to a detailed study of the surface of the planet and its gravitational field, a detailed study of the magnetosphere and magnetic field of Mercury, which poses a mystery to scientists, is planned. Although Mercury rotates very slowly, and its metallic core should have cooled and hardened long ago, the planet has a dipole magnetic field that is 100 times weaker than Earth's, but still maintains a magnetosphere around the planet. The modern theory of magnetic field generation in celestial bodies, the so-called theory of turbulent dynamo, requires the presence in the interior of the planet of a layer of liquid conductor of electricity (for the Earth this is the outer part of the iron core) and relatively rapid rotation. For what reason Mercury's core still remains liquid is not yet clear.

Mercury has an amazing feature that no other planet has. The movement of Mercury in its orbit around the Sun and its rotation around its axis are clearly synchronized with each other: during two orbital periods it makes three revolutions around its axis. Generally speaking, astronomers have been familiar with synchronous motion for a long time: our Moon synchronously rotates around its axis and revolves around the Earth, the periods of these two movements are the same, i.e. they are in a 1:1 ratio. And other planets have some satellites that exhibit the same feature. This is the result of the tidal effect.

To follow the movement of Mercury (fig. above), let's place an arrow on its surface. It can be seen that in one revolution around the Sun, i.e. in one Mercury year, the planet rotated around its axis exactly one and a half times. During this time, day in the area of ​​the arrow turned into night, and half of the sunny day passed. Another annual revolution - and daylight begins again in the area of ​​the arrow, one solar day has expired. Thus, on Mercury, a solar day lasts two Mercury years.

We will talk about tides in detail in Chap. 6. It was as a result of tidal influence from the Earth that the Moon synchronized its two movements - axial rotation and orbital rotation. The Earth greatly influences the Moon: it stretches its figure and stabilizes its rotation. The Moon's orbit is close to circular, so the Moon moves along it at an almost constant speed at an almost constant distance from the Earth (we discussed the extent of this "almost" in Chapter 1). Therefore, the tidal effect varies slightly and controls the rotation of the Moon along its entire orbit, leading to a 1:1 resonance.

Unlike the Moon, Mercury moves around the Sun in a substantially elliptical orbit, sometimes approaching the luminary, sometimes moving away from it. When it is far away, near the aphelion of the orbit, the tidal influence of the Sun weakens, since it depends on distance as 1/ R 3. When Mercury approaches the Sun, the tides are much stronger, so only in the perihelion region does Mercury effectively synchronize its two movements - diurnal and orbital. Kepler's second law tells us that the angular velocity of orbital motion is maximum at the perihelion point. It is there that “tidal capture” and synchronization of Mercury’s angular velocities – daily and orbital – occurs. At the perihelion point they are exactly equal to each other. Moving further, Mercury almost ceases to feel the tidal influence of the Sun and maintains its angular velocity of rotation, gradually reducing the angular velocity of orbital motion. Therefore, in one orbital period it manages to make one and a half daily revolutions and again falls into the clutches of the tidal effect. Very simple and beautiful physics.

The surface of Mercury is almost indistinguishable from the moon. Even professional astronomers, when the first detailed photographs of Mercury appeared, showed them to each other and asked: “Well, guess, is this the Moon or Mercury?” It's really hard to guess. Both there and there are surfaces battered by meteorites. But, of course, there are features. Although there are no large lava seas on Mercury, its surface is not homogeneous: there are older and younger areas (the basis for this is the count of meteorite craters). Mercury also differs from the Moon in the presence of characteristic ledges and folds on the surface, which arose as a result of the compression of the planet as its huge metal core cooled.

Temperature differences on the surface of Mercury are greater than on the Moon. During the daytime at the equator it is 430 °C, and at night –173 °C. But Mercury’s soil serves as a good heat insulator, so at a depth of about 1 m daily (or biannual?) temperature changes are no longer felt. So, if you fly to Mercury, the first thing you need to do is dig a dugout. It will be about 70 °C at the equator; It's a bit hot. But in the region of the geographic poles in the dugout it will be about –70 °C. So you can easily find the geographic latitude at which you will be comfortable in the dugout.

The lowest temperatures are observed at the bottom of polar craters, where the sun's rays never reach. It was there that deposits of water ice were discovered, which had previously been detected by radars from the Earth, and then confirmed by instruments of the MESSENGER space probe. The origin of this ice is still debated. Its sources can be both comets and water vapor emerging from the bowels of the planet.

Mercury has one of the largest impact craters in the Solar System - Heat Planum ( Caloris Basin) with a diameter of 1550 km. This is the impact of an asteroid with a diameter of at least 100 km, which almost split the small planet. This happened about 3.8 billion years ago, during the period of the so-called “late heavy bombardment” ( Late Heavy Bombardment), when, for reasons that are not fully understood, the number of asteroids and comets in orbits intersecting the orbits of terrestrial planets increased.

When Mariner 10 photographed the Heat Plane in 1974, we did not yet know what happened on the opposite side of Mercury after this terrible impact. It is clear that if the ball is hit, sound and surface waves are excited, which propagate symmetrically, pass through the “equator” and gather at the antipodeal point, diametrically opposite to the point of impact. The disturbance there contracts to a point, and the amplitude of seismic vibrations rapidly increases. This is similar to the way cattle drivers crack their whip: the energy and momentum of the wave is essentially conserved, but the thickness of the whip tends to zero, so the vibration speed increases and becomes supersonic. It was expected that in the region of Mercury opposite the basin Caloris there will be a picture of incredible destruction. In general, it almost turned out that way: there was a vast hilly area with a corrugated surface, although I expected there to be an antipodean crater. It seemed to me that when the seismic wave collapses, a “mirror” phenomenon will occur to the fall of the asteroid. We observe this when a drop falls on a calm surface of water: first it creates a small depression, and then the water rushes back and throws a small new drop upward. This did not happen on Mercury, and we now understand why. Its depths turned out to be heterogeneous and precise focusing of the waves did not occur.

In general, the relief of Mercury is smoother than that of the Moon. For example, the walls of Mercury's craters are not so high. The likely reason for this is the greater force of gravity and the warmer and softer interior of Mercury.

Venus- the second planet from the Sun and the most mysterious of the terrestrial planets. It is not clear what the origin of its very dense atmosphere, consisting almost entirely of carbon dioxide (96.5%) and nitrogen (3.5%) and causing a powerful greenhouse effect, is. It is not clear why Venus rotates so slowly around its axis - 244 times slower than the Earth, and also in the opposite direction. At the same time, the massive atmosphere of Venus, or rather its cloud layer, flies around the planet in four Earth days. This phenomenon is called atmospheric superrotation. At the same time, the atmosphere rubs against the surface of the planet and should have slowed down long ago. After all, it cannot move for a long time around a planet whose solid body practically stands still. But the atmosphere rotates, and even in the direction opposite to the rotation of the planet itself. It is clear that friction with the surface dissipates the energy of the atmosphere, and its angular momentum is transferred to the body of the planet. This means that there is an influx of energy (obviously solar), due to which the heat engine operates. Question: how is this machine implemented? How is the energy of the Sun transformed into the movement of the Venusian atmosphere?

Due to the slow rotation of Venus, the Coriolis forces on it are weaker than on Earth, so atmospheric cyclones there are less compact. In fact, there are only two of them: one in the northern hemisphere, the other in the southern hemisphere. Each of them “winds” from the equator to its own pole.

The upper layers of the Venusian atmosphere were studied in detail by flybys (carrying out a gravity maneuver) and orbital probes - American, Soviet, European and Japanese. Soviet engineers launched Venera series devices there for several decades, and this was our most successful breakthrough in the field of planetary exploration. The main task was to land the descent module on the surface to see what was there under the clouds.

The designers of the first probes, like the authors of science fiction works of those years, were guided by the results of optical and radio astronomical observations, from which it followed that Venus is a warmer analogue of our planet. That is why in the middle of the 20th century all science fiction writers - from Belyaev, Kazantsev and Strugatsky to Lem, Bradbury and Heinlein - presented Venus as inhospitable (hot, swampy, with a poisonous atmosphere), but in general earth-like world. For the same reason, the first landing vehicles of the Venus probes were not very durable, unable to withstand high pressure. And they died, descending into the atmosphere, one after another. Then their bodies began to be made stronger, designed for a pressure of 20 atmospheres. But this turned out to be not enough. Then the designers, “biting the bit,” made a titanium probe that can withstand a pressure of 180 atm. And he landed safely on the surface (“Venera-7”, 1970). Note that not every submarine can withstand such pressure, which prevails at a depth of about 2 km in the ocean. It turned out that the pressure on the surface of Venus does not drop below 92 atm (9.3 MPa, 93 bar), and the temperature is 464 °C.

The dream of a hospitable Venus, similar to the Earth of the Carboniferous period, was finally ended precisely in 1970. For the first time, a device designed for such hellish conditions (“Venera-8”) successfully descended and worked on the surface in 1972. From this moment of landing to the surface of Venus have become a routine operation, but it is not possible to work there for a long time: after 1-2 hours the inside of the device heats up and the electronics fail.

The first artificial satellites appeared near Venus in 1975 (“Venera-9 and -10”). In general, the work on the surface of Venus by the Venera-9...-14 descent vehicles (1975-1981) turned out to be extremely successful, studying both the atmosphere and the surface of the planet at the landing site, even managing to take soil samples and determine it chemical composition and mechanical properties. But the greatest effect among fans of astronomy and cosmonautics was caused by the photo panoramas they transmitted of the landing sites, first in black and white, and later in color. By the way, the Venusian sky, when viewed from the surface, is orange. Beautiful! Until now (2017), these images remain the only ones and are of great interest to planetary scientists. They continue to be processed and new parts are found on them from time to time.

American astronautics also made a significant contribution to the study of Venus in those years. The Mariner 5 and 10 flybys studied the upper atmosphere. Pioneer Venera 1 (1978) became the first American Venus satellite and carried out radar measurements. And “Pioneer-Venera-2” (1978) sent 4 descent vehicles into the planet’s atmosphere: one large (315 kg) with a parachute to the equatorial region of the daytime hemisphere and three small (90 kg each) without parachutes - to mid-latitudes and at the north of the day hemisphere, as well as the night hemisphere. None of them were designed to work on the surface, but one of the small devices landed safely (without a parachute!) and worked on the surface for more than an hour. This case allows you to feel how high the density of the atmosphere is near the surface of Venus. The atmosphere of Venus is almost 100 times more massive than the Earth's atmosphere, and its density at the surface is 67 kg/m 3, which is 55 times denser than Earth's air and only 15 times less dense than liquid water.

It was not easy to create strong scientific probes that can withstand the pressure of the Venusian atmosphere, the same as at a kilometer depth in our oceans. But it was even more difficult to get them to withstand the ambient temperature of 464 ° C in the presence of such dense air. The heat flow through the body is colossal. Therefore, even the most reliable devices worked for no more than two hours. In order to quickly descend to the surface and prolong its work there, the Venus dropped its parachute during landing and continued its descent, slowed down only by a small shield on its hull. The impact on the surface was softened by a special damping device - a landing support. The design turned out to be so successful that Venera 9 landed on a slope with an inclination of 35° without any problems and worked normally.

Given Venus's high albedo and colossal density of its atmosphere, scientists doubted there would be enough sunlight near the surface to photograph. In addition, a dense fog could well be hanging at the bottom of the gas ocean of Venus, scattering sunlight and preventing a contrast image from being obtained. Therefore, the first landing vehicles were equipped with halogen mercury lamps to illuminate the soil and create light contrast. But it turned out that there is quite enough natural light there: it is as light on Venus as on a cloudy day on Earth. And the contrast in natural light is also quite acceptable.

In October 1975, the Venera 9 and 10 landing vehicles, through their orbital blocks, transmitted to Earth the first ever photographs of the surface of another planet (if we do not take into account the Moon). At first glance, the perspective in these panoramas looks strangely distorted: the reason is the rotation of the shooting direction. These images were taken by a telephotometer (optical-mechanical scanner), the “look” of which slowly moved from the horizon under the feet of the landing vehicle and then to the other horizon: a 180° scan was obtained. Two telephotometers on opposite sides of the device were supposed to provide a complete panorama. But the lens caps did not always open. For example, on “Venera-11 and -12” none of the four opened.

One of the most beautiful experiments in the study of Venus was carried out using the VeGa-1 and -2 probes (1985). Their name stands for “Venus-Halley”, because after the separation of the descent modules aimed at the surface of Venus, the flight parts of the probes went to explore the nucleus of Comet Halley and for the first time did so successfully. The landing devices were also not entirely ordinary: the main part of the device landed on the surface, and during descent, a balloon made by French engineers was separated from it, and for about two days it flew in the atmosphere of Venus at an altitude of 53-55 km, transmitting data on temperature and pressure to Earth , illumination and visibility in clouds. Thanks to the powerful wind blowing at this altitude at a speed of 250 km/h, the balloons managed to fly around a significant part of the planet. Beautiful!

Photographs from the landing sites show only small areas of the Venusian surface. Is it possible to see all of Venus through the clouds? Can! The radar sees through the clouds. Two Soviet satellites with side-looking radars and one American flew to Venus. Based on their observations, radio maps of Venus were compiled with very high resolution. On general map it is difficult to demonstrate, but it is clearly visible on certain fragments of the map. The colors on the radio maps show the levels: light blue and dark blue are lowlands; If Venus had water, it would be oceans. But liquid water cannot exist on Venus. And there is practically no gaseous water there either. Greenish and yellowish are the continents, let's call them that. Red and white are the most high points on Venus. This is the “Venusian Tibet” - the highest plateau. The highest peak on it, Mount Maxwell, rises 11 km.

There are no reliable facts about the depths of Venus, about its internal structure, since seismic research has not yet been carried out there. In addition, the slow rotation of the planet does not allow measuring its moment of inertia, which could tell us about the distribution of density with depth. So far, theoretical ideas are based on the similarity of Venus with the Earth, and the apparent absence of plate tectonics on Venus is explained by the absence of water on it, which on Earth serves as a “lubricant”, allowing the plates to slide and dive under each other. Coupled with the high surface temperature, this leads to a slowdown or even complete absence of convection in the body of Venus, reduces the cooling rate of its interior and may explain its lack of a magnetic field. All this looks logical, but requires experimental verification.

By the way, about Earth. I will not discuss the third planet from the Sun in detail, since I am not a geologist. In addition, each of us has a general idea of ​​the Earth, even based on school knowledge. But in connection with the study of other planets, I note that we also do not fully understand the interior of our own planet. Almost every year there are major discoveries in geology, sometimes even new layers are discovered in the bowels of the Earth. We don't even know exactly the temperature at the core of our planet. Look at the latest reviews: some authors believe that the temperature at the boundary of the inner core is about 5000 K, while others believe that it is more than 6300 K. These are the results of theoretical calculations, which include not entirely reliable parameters that describe the properties of matter at a temperature of thousands of kelvins and a pressure of millions bar. Until these properties are reliably studied in the laboratory, we will not receive accurate knowledge about the interior of the Earth.

The uniqueness of the Earth among similar planets lies in the presence of a magnetic field and liquid water on the surface, and the second, apparently, is a consequence of the first: the Earth’s magnetosphere protects our atmosphere and, indirectly, the hydrosphere from solar wind flows. To generate a magnetic field, as it now appears, in the interior of the planet there must be a liquid electrically conductive layer, covered by convective motion, and rapid daily rotation, providing the Coriolis force. Only under these conditions does the dynamo mechanism turn on, enhancing the magnetic field. Venus barely rotates, so it has no magnetic field. The iron core of little Mars has long cooled and hardened, so it also lacks a magnetic field. Mercury, it would seem, rotates very slowly and should have cooled down before Mars, but it has a quite noticeable dipole magnetic field with a strength 100 times weaker than the Earth’s. Paradox! The tidal influence of the Sun is now believed to be responsible for maintaining Mercury's iron core in a molten state. Billions of years will pass, the iron core of the Earth will cool and harden, depriving our planet of magnetic protection from the solar wind. And the only rocky planet with a magnetic field will remain, oddly enough, Mercury.

Now let's turn to Mars. Its appearance immediately attracts us for two reasons: even in photographs taken from afar, the white polar caps and translucent atmosphere are visible. This is similar between Mars and the Earth: the polar caps give rise to the idea of ​​the presence of water, and the atmosphere – the possibility of breathing. And although on Mars not everything is as good with water and air as it seems at first glance, this planet has long attracted researchers.

Previously, astronomers studied Mars through a telescope and therefore eagerly awaited moments called “Mars oppositions.” What is opposing what at these moments?

From the point of view of an earthly observer, at the moment of opposition, Mars is on one side of the Earth, and the Sun is on the other. It is clear that it is at these moments that the Earth and Mars approach the minimum distance, Mars is visible in the sky all night and is well illuminated by the Sun. Earth orbits the Sun every year, and Mars every 1.88 years, so the average time between oppositions is just over two years. The last opposition of Mars was in 2016, although it was not particularly close. Mars's orbit is noticeably elliptical, so Earth's closest approaches to Mars occur when Mars is near the perihelion of its orbit. On Earth (in our era) this is the end of August. Therefore, the August and September confrontations are called “great”; At these moments, which occur once every 15-17 years, our planets come closer to each other by less than 60 million km. This will happen in 2018. And a super-close confrontation took place in 2003: then Mars was only 55.8 million km away. In this regard, a new term was born - “the greatest oppositions of Mars”: these are now considered approaches of less than 56 million km. They occur 1-2 times a century, but in the current century there will be even three of them - wait for 2050 and 2082.

But even during moments of great opposition, little is visible on Mars through a telescope from Earth. Here is a drawing of an astronomer looking at Mars through a telescope. An unprepared person will look and be disappointed - he will not see anything at all, just a small pink “drop”. But with the same telescope, the experienced eye of an astronomer sees more. Astronomers noticed the polar cap a long time ago, centuries ago. And also dark and light areas. The dark ones were traditionally called seas, and the light ones – continents.

Increased interest in Mars arose during the era of the great opposition of 1877: - by that time, good telescopes had already been built, and astronomers had made several important discoveries. American astronomer Asaph Hall discovered the moons of Mars - Phobos and Deimos. And the Italian astronomer Giovanni Schiaparelli sketched mysterious lines on the surface of the planet - Martian canals. Of course, Schiaparelli was not the first to see the channels: some of them were noticed before him (for example, Angelo Secchi). But after Schiaparelli, this topic became dominant in the study of Mars for many years.

Observations of features on the surface of Mars, such as “channels” and “seas,” marked the beginning of a new stage in the study of this planet. Schiaparelli believed that the “seas” of Mars could indeed be bodies of water. Since the lines connecting them needed to be given a name, Schiaparelli called them “canals” (canali), meaning sea straits, and not man-made structures. He believed that water actually flows through these channels in the polar regions during the melting of the polar caps. After the discovery of “channels” on Mars, some scientists suggested their artificial nature, which served as the basis for hypotheses about the existence of intelligent beings on Mars. But Schiaparelli himself did not consider this hypothesis scientifically substantiated, although he did not exclude the presence of life on Mars, perhaps even intelligent.

However, the idea of ​​an artificial irrigation canal system on Mars began to gain ground in other countries. This was partly due to the fact that the Italian canali was represented in English as canal (man-made waterway), rather than channel (natural sea strait). And in Russian the word “canal” means an artificial structure. The idea of ​​Martians captivated many people at that time, and not only writers (remember H.G. Wells with his “War of the Worlds,” 1897), but also researchers. The most famous of them was Percival Lovell. This American received an excellent education at Harvard, equally mastering mathematics, astronomy and humanities. But as the scion of a noble family, he would rather become a diplomat, writer or traveler than an astronomer. However, after reading Schiaparelli's works on canals, he became fascinated by Mars and believed in the existence of life and civilization on it. In general, he abandoned all other matters and began studying the Red Planet.

With money from his wealthy family, Lovell built an observatory and began drawing canals. Note that photography was then in its infancy, and the eye of an experienced observer is able to notice the smallest details in conditions of atmospheric turbulence, distorting images of distant objects. The maps of Martian canals created at the Lovell Observatory were the most detailed. In addition, being a good writer, Lovell wrote several interesting books - Mars and its channels (1906), Mars as the abode of life(1908), etc. Only one of them was translated into Russian even before the revolution: “Mars and life on it” (Odessa: Matezis, 1912). These books captivated an entire generation with the hope of meeting Martians.

It should be admitted that the story of the Martian canals has never received a comprehensive explanation. There are old drawings with channels and modern photographs without them. Where are the channels? What was it? Astronomers' conspiracy? Mass insanity? Self-hypnosis? It is difficult to blame scientists who have given their lives to science for this. Perhaps the answer to this story lies ahead.

And today we study Mars, as a rule, not through a telescope, but with the help of interplanetary probes. (Although telescopes are still used for this and sometimes bring important results.) The flight of probes to Mars is carried out along the most energetically favorable semi-elliptical trajectory. Using Kepler's Third Law, it is easy to calculate the duration of such a flight. Due to the high eccentricity of the Martian orbit, the flight time depends on the launch season. On average, a flight from Earth to Mars lasts 8-9 months.

Is it possible to send a manned expedition to Mars? It's big and interesting topic. It would seem that all that is needed for this is a powerful launch vehicle and a convenient spaceship. No one yet has sufficiently powerful carriers, but American, Russian and Chinese engineers are working on them. There is no doubt that such a rocket will be created in the coming years by state-owned enterprises (for example, our new Angara rocket in its most powerful version) or private companies (Elon Musk - why not).

Is there a ship in which astronauts will spend many months on their way to Mars? There is no such thing yet. All existing ones (Soyuz, Shenzhou) and even those undergoing testing (Dragon V2, CST-100, Orion) are very cramped and are only suitable for flying to the Moon, where it is only 3 days away. True, there is an idea to inflate additional rooms after takeoff. In the fall of 2016, the inflatable module was tested on the ISS and performed well. Thus, the technical possibility of flying to Mars will soon appear. So what's the problem? In a person!

We are constantly exposed to natural radioactivity of the earth's rocks, streams of cosmic particles or artificially created radioactivity. At the Earth's surface, the background is weak: we are protected by the magnetosphere and atmosphere of the planet, as well as its body, covering the lower hemisphere. In low Earth orbit, where ISS cosmonauts work, the atmosphere no longer helps, so the background radiation increases hundreds of times. In outer space it is even several times higher. This significantly limits the duration of a person’s safe stay in space. Let us note that nuclear industry workers are prohibited from receiving more than 5 rem per year - this is almost safe for health. Cosmonauts are allowed to receive up to 10 rem per year (an acceptable level of danger), which limits the duration of their work on the ISS to one year. And a flight to Mars with a return to Earth, in the best case (if there are no powerful flares on the Sun), will lead to a dose of 80 rem, which will create a high probability of cancer. This is precisely the main obstacle to human flight to Mars. Is it possible to protect astronauts from radiation? Theoretically, it’s possible.

We are protected on Earth by an atmosphere whose thickness per square centimeter is equivalent to a 10-meter layer of water. Light atoms better dissipate the energy of cosmic particles, so the protective layer of a spacecraft can be 5 meters thick. But even in a cramped ship, the mass of this protection will be measured in hundreds of tons. Sending such a ship to Mars is beyond the power of a modern or even promising rocket.

OK then. Let's say there were volunteers who were ready to risk their health and go to Mars in one direction without radiation protection. Will they be able to work there after landing? Can they be counted on to complete the task? Remember how astronauts, after spending six months on the ISS, feel immediately after landing on the ground? They are carried out in their arms, placed on a stretcher, and for two to three weeks they are rehabilitated, restoring bone strength and muscle strength. And on Mars no one will carry them in their arms. There you will need to go out on your own and work in heavy void suits, like on the Moon. After all, the atmospheric pressure on Mars is practically zero. The suit is very heavy. On the Moon it was relatively easy to move in it, since the gravity there is 1/6 of the Earth's, and during the three days of flight to the Moon the muscles do not have time to weaken. Astronauts will arrive on Mars after spending many months in conditions of weightlessness and radiation, and the gravity on Mars is two and a half times greater than the lunar one. In addition, on the surface of Mars itself, the radiation is almost the same as in outer space: Mars has no magnetic field, and its atmosphere is too rarefied to serve as protection. So the movie “The Martian” is fantasy, very beautiful, but unreal.

How did we imagine a Martian base before? We arrived, set up laboratory modules on the surface, live and work in them. And now here’s how: we flew in, dug in, built shelters at a depth of at least 2-3 meters (this is quite reliable protection from radiation) and try to go to the surface less often and not for long. Resurrections are sporadic. We basically sit under the ground and control the work of the Mars rovers. So they can be controlled from Earth, even more efficiently, cheaper and without risk to health. This is what has been done for several decades.

About what robots learned about Mars - .

Illustrations prepared by V. G. Surdin and N. L. Vasilyeva using NASA photographs and images from public sites

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 emergence and further development living matter, 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 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, within 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. Careful examination reveals another most interesting feature, which 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. His average depth about 3.8 km, 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 in the Universe natural conditions, 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.

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 about 3.3 to 9.7 g/cm³. In the crust and (partially) in the mantle there are extensive lithospheric plates. 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/s².

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 closest to us heavenly body. 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.

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 deep depressions On 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 far from volcanoes northern hemisphere sand dunes stretch out. There are especially many of them near the northern polar cap.

The abundance of volcanic landscapes indicates that in the distant past Mars experienced quite a turbulent geological epoch, 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, highest peak 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 terrestrial volcanoes 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 got their 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 spacecraft series "Viking" three complex biological experiments were performed: pyrolysis decomposition, gas exchange, 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 nature. So, we can summarize that Mars is a planet that does not have the conditions for the emergence of life.

Conclusion

We met current state our planet and the planets of the Terrestrial 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.

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 much it actually was terrestrial planets when the solar system 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.