Krenev Evgenia
The work describes the planets belonging to the Earth group. The conditions on these planets, their common features, as well as the features of each planet are considered.
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PLANETS OF THE EARTH GROUP Presentation on astronomy Prepared by a student of grade 11 Krenyova Evgenia Secondary School No 8 of Moscow
SOLAR SYSTEM
Terrestrial Planets These are the four planets of the Solar System: Mercury, Venus, Earth and Mars. They are also called the inner planets, in contrast to the outer planets - the giant planets.
The terrestrial planets have a high density and consist mainly of silicates and metallic, as well as oxygen, silicon, iron, magnesium, aluminum and other heavy elements. The largest planet of the terrestrial group is Earth, but it is more than 14 times inferior in mass to the least massive gas planet, Uranus. All the terrestrial planets have the following structure: - in the center a core of iron with an admixture of nickel, - a mantle, consists of silicates, - a crust formed as a result of partial melting of the mantle and also consisting of silicate rocks, but enriched with incompatible elements. Of the terrestrial planets, there is no crust in Mercury, which is explained by its destruction as a result of meteorite bombardment.
MERCURY Is located closest to the sun. The existence of this planet was mentioned in the ancient Sumerian writings, which date back to the third millennium BC. The name of this planet is grateful to the Roman pantheon Mercury, the patron saint of merchants, who also had his Greek counterpart - Hermes. Mercury completely passes around the sun for eighty-eight days of the earth. It bypasses around its axis in less than sixty days, which is two-thirds of a year by mercurian standards. The temperature on the surface of mercury can vary very much - from + 430 degrees on the side of the sun and up to + 180 degrees from the shadow side. In our solar system, these drops are the strongest.
MERCURY Mercury can observe such an unusual phenomenon, which was called the effect of Joshua. When the sun on Mercury reaches a certain point, it stops and starts to go in the opposite direction, and not like on Earth - it should go around a full circle around the planet. Mercury is the smallest planet in the Earth group. It is inferior in size even to the largest satellites of the planets Jupiter and Saturn. The surface of Mercury is similar to the surface of the Moon - the whole is covered with craters. The only difference with the lunar surface - on Mercury there are numerous oblique jagged slopes, which can stretch for many hundreds of kilometers. These slopes were formed as a result of compression when the planet cooled.
MERCURY One of the most popular and visible parts of the planet is the so-called Plain of Heat. This is a crater, which got its name because of its proximity to the “hot longitudes”. The crater has a diameter of one thousand three hundred kilometers. Most likely, the celestial body, which in ancient times made this crater, had a diameter of at least one hundred kilometers. Thanks to gravity, Mercury also captures particles of the solar wind, which in turn make the atmosphere around Mercury quite relaxed. And they are replaced every two hundred days. In addition, this planet is the fastest planet of our system. The average speed of its rotation around the sun is about forty-seven and a half kilometers per second, which is twice as fast as the Earth.
VENUS The atmosphere of Venus is rather aggressive, because it has a very high temperature relative to the Earth and there are poisonous clouds in the sky. The atmosphere of Venus consists mainly of carbon dioxide alone. If you find yourself in the atmosphere of this planet, then the pressure will be about eighty-five kg to 1 square centimeter. In the Earth’s atmosphere, the pressure will be eighty-five times less. If you throw a coin in the atmosphere of Venus, it will fall as if in a layer of water. Thus, walking on the surface of this planet is just as difficult as at the bottom of the ocean. And if God forbid, the wind will rise on Venus, then it will carry you like a wave of the sea wave.
VENUS The atmosphere of this planet is 96% carbon dioxide. It is because of this that the greenhouse effect is created. The surface of the planet is heated by the sun, and the heat generated cannot be dissipated in space because it is reflected by a layer of carbon dioxide. That is why the temperature of this planet is about four hundred and eighty degrees, like in the oven.
VENUS Thousands of volcanoes are dotted on the surface of Venus. Fantasists described Venus as Earth-like. Believed that Venus envelop the clouds. And this means that the surface of this planet must be littered with swamps. This means that there is probably a very rainy climate, which leads to high clouds and high humidity. In reality, everything is completely different - in the early seventies, the union sent spacecraft to the surface of Venus, which clarified the situation. It turned out that the surface of this planet is made up of solid rocky deserts, where water is completely absent. Of course, with such a high temperature, no water could ever be.
EARTH Earth is fifth in size and mass among the major planets, but from the terrestrial planets, it is the largest. The most important difference from the other planets of the Solar System is the existence of life on it, which with the advent of man has reached its highest, rational form. According to modern cosmogonical ideas, the Earth was formed ~ 4.5 billion years ago by gravitational condensation from a gas-dust substance scattered in the near-solar space, containing all the chemical elements known in nature.
EARTH The formation of the Earth was accompanied by the differentiation of matter, which was promoted by the gradual warming up of the earth's interior, mainly due to the heat released during the decay of radioactive elements (uranium, thorium, potassium, etc.). The result of this differentiation was the division of the Earth into concentrically located layers - geospheres, differing in chemical composition, state of aggregation and physical properties. In the center formed the core of the Earth, surrounded by the mantle. Of the lightest and fusible components of the substance released from the mantle in the smelting process, an earth crust located above the mantle arose. The combination of these internal geospheres bounded by a solid earth's surface is sometimes called the “solid” Earth.
EARTH "Solid" Earth encloses almost the entire mass of the planet. Outside it are external geospheres - water (hydrosphere) and air (atmosphere), which were formed from the vapors and gases released from the bowels of the Earth during the degassing of the mantle. The differentiation of the substance of the Earth’s mantles and the replenishment by products of differentiation of the Earth’s crust, water and air shells occurred throughout the geological history and continue to this day.
MARS Named this planet in honor of the famous god of War in Rome, because the color of this planet is very much like the color of blood. This planet is also called the “red planet”. It is assumed that this color of the planet is associated with iron oxide, which is present in the atmosphere of Mars. Mars is the seventh largest planet in the solar system. It is considered to be the home of the Mariner Valley - it is a canyon that is much longer and deeper than the famous Grand Canyon in the United States. By the way, there are mountains on Mars, which are not small, and the height of these mountains is sometimes much higher than our Everest. Here, by the way, there is also Olympus - the highest and most famous mountain in the entire solar system.
MARS Mars has the largest volcanoes in the solar system. But the atmosphere of this planet with a density of a hundred times less than the Earth. But this is enough to maintain the weather system on the planet - this means wind and clouds. The average temperature of Mars boasts at minus sixty degrees. Year on Mars = 687 days of terrestrial calculation. But the day on Mars is as close to Earth day as possible - it is 24 hours, 39 minutes. and 35 sec. Mars has a very thick crust - about fifty kilometers in cross section. And Mars has two moons - Deimos and Phobos.
Thanks for attention!
Introduction
Among the numerous celestial bodies studied by modern astronomy, the planets occupy a special place. After all, we all know well that the Earth on which we live is a planet, so the planets are bodies, basically similar to our Earth.
But in the world of planets, we will not meet even two completely alike. The variety of physical conditions on the planets is very large. The distance of the planet from the Sun (and hence the amount of solar heat, and the surface temperature), its dimensions, gravity stress on the surface, the orientation of the axis of rotation, determining the change of seasons, the presence and composition of the atmosphere, the internal structure and many other properties are different for all of nine planets of the solar system.
Speaking about the diversity of conditions on the planets, we can learn more deeply the laws of their development and find out their interrelation between these or other properties of the planets. For example, its ability to hold the atmosphere of a composition depends on the size, mass and temperature of the planet, and the presence of the atmosphere in turn affects the thermal regime of the planet.
As the study shows the conditions under which the birth and further development of living matter is possible, only on the planets can we look for signs of the existence of organic life. That is why the study of the planets, in addition to the 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, and for other areas of science, primarily 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 closest planet to the Sun of the solar system. The average distance from Mercury to the Sun is only 58 million km. Among the major planets, it has the smallest dimensions: its diameter is 4865 km (0.38 of the diameter of the Earth), mass is 3.304 * 10 23 kg (0.055 is the mass of the Earth, or 1: 6025000 is the mass of the Sun); average density of 5.52 g / cm 3. Mercury is a bright star, but to see it in the sky is not so simple. 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 to the left (to the east), then to the right (to the west) only a short distance that does not exceed 28 O. Therefore, it can see only in those days of the year when it departs from the Sun at the greatest distance. Suppose, for example, Mercury moved away from the Sun to the left. The sun and all the stars in their daily movement float through the sky from left to right. Therefore, the sun first sets, and after an hour with a little Mercury sets, it is necessary to search for this planet low above the Western horizon.
Motion.
Mercury moves around the Sun on average at a 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 in aphelion 70 million km. The planet flies around the Sun in three Earth months or in 88 days at a speed of 47.9 km / s. Moving along its path around the Sun, Mercury at the same time turns around its axis so that always one and the same half of it is facing the Sun. This means that on one side of Mercury is always day, and on the other - night. In the 60s. using radar observations, it was found that Mercury rotates around an axis in the forward direction (that is, as in orbital motion) with a period of 58.65 days (relative to the stars). The duration of the solar day on Mercury is 176 days. The equator is inclined to the plane of its orbit by 7 °. The angular velocity of the axial rotation of Mercury is 3/2 of the orbital and corresponds to the angular velocity 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 be deprived of the atmosphere, although polarization and spectral observations indicate the presence of a weak atmosphere. With the help of “Mariner-10”, the presence of a highly discharged gas envelope, consisting mainly of helium, was found in Mercury. This atmosphere is in dynamic equilibrium: each helium atom is in it for about 200 days, after which it leaves the planet, while another particle from the plasma of the solar wind takes its place. In addition to helium, an insignificant amount of hydrogen was found in the atmosphere of Mercury. It is about 50 times smaller than helium.
It also turned out that Mercury has a weak magnetic field, the intensity of which is only 0.7% of the earth. The slope of the dipole axis to the axis of rotation of Mercury is 12 0 (the Earth has 11 0)
The pressure at the surface of the planet is about 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 and warms it 7 times stronger than ours. On the day side of Mercury is terribly hot, there is an eternal hell there. Measurements show that the temperature there rises to 400 o above zero. But on the night side there should always be a strong 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 ice desert, perhaps covered with frozen gases.
Surface.
From the flight path of the Mariner 10 spacecraft in 1974, more than 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 was in darkness from Earth. The abundance of craters is the most obvious feature of its surface, which in its first impression can be likened to the Moon.
Indeed, the morphology of craters is close to lunar, their impact origin is unquestionable: the majority of the shaft has delineated traces of emissions of the material crushed upon impact with the formation of characteristic bright rays and the field of secondary craters in some cases. Many craters have a central hill and a terraced structure on the inner slope. It is interesting that not only practically all large craters with a diameter of more than 40-70 km have such features, but also a much larger number of craters of smaller size, within 5-70 km (of course, we are talking about well-preserved craters). These features can be attributed both to the expense of the greater kinetic energy of bodies that fell to the surface, and to the expense of the surface material itself.
The degree of erosion and smoothing of craters varies. In general, the Mercury craters are less deep compared to the lunar craters, 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 than on the Moon, and deposits of crushed material to a lesser extent mask the primary forms of relief. The secondary craters themselves are deeper than lunar craters, which again is explained by the fact that the fragments falling to the surface experience a greater acceleration of gravity.
Just like on the Moon, depending on the relief, it is possible to distinguish the prevailing uneven “mainland” and much smoother “sea” areas. The latter are mainly hollows, which, however, are significantly smaller than on the moon, their dimensions usually do not exceed 400-600 km. In addition, some basins are poorly distinguishable against the background of the surrounding relief. The exception is the mentioned extensive Canoris Basin (Sea of Heat) about 1300 km long, resembling the famous Sea of Rains on the Moon.
In the predominant continental part of the surface of Mercury, it is possible to distinguish both highly craterized areas, with the greatest degree of crater degradation, and the old inter-crater plateaus, which occupy vast territories, indicating a widely developed ancient volcanism. These are the most ancient preserved relief forms of the planet. The flattened 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 strokes resembling the moon. Some of the flat areas adjacent to the basins were probably formed during the deposition of material thrown out of them. At the same time, for most of the plains, quite definite evidence of their volcanic origin has been found, however, this volcanism is later than on the inter-crater plateaus. Careful examination reveals another interesting feature that sheds light on the history of the formation of the planet. We are talking about the characteristic traces of tectonic activity on a global scale in the form of specific steep ledges, or escarpment slopes. Escarpes have a length of 20-500 km and a height of slopes from a few hundred meters to 1-2 km. In their morphology and geometry of location on the surface, they differ from the usual tectonic discontinuities and discharges observed on the Moon and Mars, and were rather formed due to thrusts, stratifications due to the stress in the surface layer that occurred during the compression of Mercury. This is evidenced by the horizontal displacement of the shafts of some craters.
Some of the escapes were bombarded and partially destroyed. This means that they formed earlier than craters on their surface. By narrowing the erosion of these craters, it can be concluded that crust compression occurred during the formation of “seas” about 4 billion years ago. The most likely cause of compression is probably to be considered the onset of the cooling of Mercury. According to another interesting suggestion put forward by a number of specialists, an alternative mechanism for the powerful tectonic activity of the planet during this period could be tidal slowing down of the planet's rotation by about 175 times: from the originally estimated value of about 8 hours to 58.6 days.
Venus.
General information.
Venus is the second closest to the Sun planet, almost the same size as the Earth, and its mass is more than 80% of the Earth’s mass. For these reasons, Venus is sometimes called the twin or sister of Earth. However, the surface and atmosphere of these two planets are completely different. On Earth, there are rivers, lakes, oceans and the atmosphere we breathe. Venus is a scorchingly 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 the circle than our planet. Venus receives more than two times more light and heat from the Sun than the Earth. Nevertheless, frost prevails from the shadow side on Venus more than 20 degrees below zero, since the sun's rays do not fall here for a very long time. The planet has a very dense, deep and very cloudy atmosphere, which does not allow us to see the surface of the planet. The atmosphere (gas envelope) was discovered by MV Lomonosov in 1761, which also showed the similarity of Venus with the Earth. The planet has no satellites.
Motion.
Venus has an almost circular orbit (eccentricity of 0.007), which it bypasses in 224.7 Earth days at a speed of 35 km / s. at a distance of 108.2 million km from the Sun. Venus makes a turn around the axis in 243 Earth days - the maximum time among all the planets. Around its axis, Venus rotates in the opposite direction, that is, in the direction opposite to the movement in orbit. Such a slow, and, moreover, reverse rotation means that, when viewed from Venus, the Sun rises and sets only twice a year, since Venusian days are 117 Earthly. The axis of rotation of Venus is almost perpendicular to the orbital plane (tilt 3 °), so there are no seasons of the year - 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 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 relatively easily pass through the clouds of its atmosphere and heat the surface of the planet, but the thermal infrared radiation of the surface itself goes 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 the global temperature by 30 ° C, and on Venus, it raises the temperature by another 400 ° C. Studying the physical consequences of the strongest greenhouse effect on Venus, we are well aware of the results that accumulation of excess heat on the Earth can cause, due to the growing concentration of carbon dioxide in the atmosphere due to the burning of fossil fuels - coal and oil.
In 1970, the first spacecraft arriving on Venus was able to withstand the terrible heat for only about one hour, but this was just enough to send data on the surface conditions to Earth.
Atmosphere.
The mysterious atmosphere of Venus has been the centerpiece of the research program with the help of automatic vehicles over the past two decades. The most important aspects of her research were chemical composition, vertical structure and dynamics of the air environment. Much attention was paid to the cloud cover, which plays the role of an insurmountable barrier for the electromagnetic waves of the optical range to penetrate deep into the atmosphere. During the television filming of Venus, it was possible to obtain an image of only the cloud cover. The extraordinary dryness of the air environment and its phenomenal greenhouse effect were incomprehensible, due to which the actual temperature of the surface and lower layers of the troposphere was more than 500 higher than the effective (equilibrium).
The atmosphere of Venus is extremely hot and dry, due to the greenhouse effect. It is a dense blanket of carbon dioxide, keeps the heat from the sun. As a result, a large amount of thermal energy accumulates. The pressure at the surface is 90 bar (as in the Earth seas at a depth of 900 m). Space ships 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 is able to act as a kind of veil, retaining 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 detected 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, while on Venus it is all concentrated in the atmosphere. In the afternoon, the surface of the planet is illuminated by diffused sunlight at about the same intensity as on an overcast day on Earth. At night, Venus has seen a lot of lightning.
The clouds of Venus are composed 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 30 km, the temperature is about 430 K. It is even lower so hot that there are no clouds. Of course, on the surface of Venus there is no liquid water. 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, making a turn 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 in diameter 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 to occur, so there is no significant weathering (weathering) there. So, volcanoes and craters have not changed much since they were formed millions of years ago.
Venus is covered in hard rocks. Red-hot lava circulates beneath them, causing tension in a thin surface layer. Lava is constantly erupting from holes and gaps in hard rock. In addition, volcanoes all the time throw out streams 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 lava bubbles form on the surface of the dome, which then fall.
On the surface of Venus, a rock rich in potassium, uranium and thorium was found, which in terrestrial conditions corresponds to the composition of not primary volcanic rocks, but secondary ones that have undergone exogenous processing. In other places on the surface lies the large-cube and block material of dark rocks with a density of 2.7-2.9 g / cm and other elements characteristic of basalt. Thus, the surface rocks of Venus turned out to be the same as on the Moon, Mercury, and Mars, which were poured out by igneous rocks of basic composition.
Little is known about the internal structure of Venus. It probably has a metal core that occupies 50% of the radius. But the planet does not have a magnetic field due to its very slow rotation.
Venus is by no means a hospitable world, as it was once supposed. 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 to be a more promising object for space exploration than Mars.
Land.
General information.
Earth is the third planet from the Sun of 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 surface area of the Earth 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 kmі, average salinity is 35 g / l. Land is respectively 29.2% and forms six continents and islands. It rises above sea level by an average of 875 m; the highest altitude (the summit of Chomolungma in the Himalayas) is 8848 m. Mountains occupy over 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and light forests - about 20%, forests - about 30%, glaciers - over 10%. Over 10% of the land is occupied by agricultural land.
The Earth has a single satellite - the Moon.
Due to its unique, perhaps the only natural conditions in the Universe, the Earth became the place where organic life arose and developed. According to modern cosmogonic ideas, the planet was formed about 4.6 - 4.7 billion years ago from a protoplanetary cloud captured by the attraction of the Sun. Formation of the first, most ancient of the studied rocks took 100-200 million years. Approximately 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 a modern type of person dates back to the time of the retreat of the first glacier, that is, about 40 thousand years ago.
Motion.
Like other planets, it moves around the Sun in an elliptical orbit, the eccentricity of which is 0.017. The distance from the Earth to the Sun at different points in the orbit varies. The average distance is about 149.6 million km. In the course of the movement of our planet 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 tilted towards the Sun with its northern hemisphere, and in others - the southern. The period of revolution around the Sun is 365.256 days, with a daily rotation of 23 hours and 56 minutes. The axis of rotation of the Earth is located at an angle of 66.5є 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 a long evolution under the influence of geological, chemical and biological processes. Perhaps the primary atmosphere of the earth was rich in hydrogen, which then evaporated. Degassing of the subsoil filled the atmosphere with carbon dioxide and water vapor. But steam condensed in the oceans, and carbon dioxide was bound in carbonate rocks. Thus, nitrogen remained in the atmosphere, and oxygen appeared gradually as a result of the life activity of the biosphere. 600 million years ago, the oxygen content in the air was 100 times lower than the current one.
Our planet is surrounded by a vast atmosphere. In accordance with the temperature, the composition and physical properties of the atmosphere can be divided into different layers. The troposphere is an area lying between the surface of the Earth and a height of 11 km. It is a rather thick and thick 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. In the troposphere there are clouds, precipitation, etc. The layer separating the troposphere from the next atmospheric layer, the stratosphere, is called the tropopause. This is an area of extremely low temperatures.
The composition of the stratosphere is the same as that of the troposphere, but ozone appears and concentrates in it. The ionosphere, that is, the ionized air layer, is formed both in the troposphere and in the lower layers. It reflects high frequency radio waves.
The atmospheric pressure at ocean level is under normal conditions about 0.1 MPa. It is believed that the earth's atmosphere has changed dramatically in the process of evolution: it was enriched with oxygen and acquired a modern composition as a result of long-term interaction with rocks and with the participation of the biosphere, that is, plant and animal organisms. Evidence that such changes really occurred, are, for example, deposits of coal and thick layers of carbonate deposits in sedimentary rocks, they contain a huge amount 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 originated from the gaseous products of volcanic eruptions; Its composition is judged by the chemical analysis of gas samples "immured" in the cavities of ancient rocks. In the studied samples, whose age is approximately 3.5 billion years, approximately 60% of carbon dioxide is contained, and the remaining 40% are sulfur compounds, ammonia, hydrogen chloride and hydrogen fluoride. Nitrogen and inert gases are found in small quantities. All oxygen was chemically bound.
For biological processes on Earth, the ozonosphere is of great importance - an ozone layer located at an altitude of 12 to 50 km. The region above 50-80 km is called the ionosphere. Atoms and molecules in this layer are intensely ionized under the influence of solar radiation, in particular, ultraviolet radiation. If it were not for the ozone layer, the radiation fluxes would reach the Earth's surface, causing destruction in the living organisms existing there. Finally, at distances of more than 1000 km, gas is so rarefied that collisions between molecules cease to play a significant role, and atoms are more than half ionized. At a height of about 1.6 and 3.7 of the Earth's radii, the first and second radiation belts are located.
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 from seismic events during natural earthquakes and as a result of explosions. Based on these studies, the Earth is conditionally divided into three areas: the crust, the mantle and the core (in the center). The outer layer - the core - has an average thickness of about 35 km. The main types of the crust are continental (continental) and oceanic; in the transition zone from the continent to the ocean, the crust of the intermediate type is developed. The thickness of the crust varies within fairly wide limits: the oceanic crust (taking into account the water layer) has a thickness of about 10 km, while the thickness of the continental crust is ten times more. Surface deposits occupy a layer about 2 km thick. Below them is a granite layer (on the continents its thickness is 20 km), and below it is approximately 14 km (both on the continents and in the oceans) basalt layer (lower crust). The density in the center of the Earth is about 12.5 g / cm. The average densities are: 2.6 g / cm_- at the surface of the Earth, 2.67 g / cm_- at granite, 2.85 g / cmі- at basalt.
The Earth’s mantle, which is also called the silicate shell, extends to a depth of approximately from 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. The densities in the mantle increase as the depth increases from approximately 3.3 to 9.7 g / cm. Extensive lithospheric plates are located in the crust and (partially) in the mantle. Their secular movements not only determine the continental drift, which significantly affects the appearance of the Earth, but also relate to the location of seismic zones on the planet. Another boundary detected by seismic methods (Gutenberg boundary) - between the mantle and the outer core - lies at a depth of 2,775 km. On it, the speed of longitudinal waves falls from 13.6 km / s (in the mantle) to 8.1 km / s (in the core), and the speed of the 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 above 5,120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth’s mass. Presumably, this is an iron-nickel alloy (80% Fe, 20% Ni).
The gravitational field of the Earth with a high accuracy is described by the law of world wide Newton. The acceleration of free fall over the surface of the Earth is determined by both the gravitational and centrifugal force due to the rotation of the Earth. The acceleration of gravity at the surface of the planet is 9.8 m / sІ.
The earth also has magnetic and electric fields. The magnetic field above the Earth’s surface is made up of constant (or varying rather slowly) and variable parts; the latter is usually referred to as magnetic field variations. The main magnetic field has a structure close to the dipole. The magnetic dipole moment of the Earth, equal to 7.98T10 ^ 25 units of the SGSM, is directed approximately opposite to the mechanical, although at present the magnetic poles are somewhat shifted relative to the geographic poles. Their position, however, changes with time, and although these changes are rather slow, for geological periods, according to paleomagnetic data, even magnetic inversions, that is, polarity inversions, are detected. The magnetic field strengths at the north and south magnetic poles are 0.58 and 0.68 Oe, respectively, and around 0.4 Oe at the geomagnetic equator.
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 a natural satellite of the Earth and the closest celestial body to us. The average distance to the moon - 384,000 kilometers, the diameter of the moon about 3476 km. The average density of the moon is 3.347 g / cm² or about 0.607 of the average density of the Earth The mass of the satellite is 73 trillion tons. Acceleration of gravity on the surface of the moon 1,623 m / sІ.
The moon moves around the Earth at an average speed of 1.02 km / s in an approximately elliptical orbit in the same direction as the vast majority of other bodies in the solar system, that is, counterclockwise, when looking at the moon's orbit from the North Pole of the world. The period of the Moon’s orbit around the Earth, the so-called sidereal month, is equal to 27.321661 days, but it is subject to slight fluctuations and a very small secular reduction.
Without being protected by the atmosphere, the surface of the moon heats up to + 110 ° C in the daytime and cools down to -120 ° C at night, however, as radio observations have shown, these huge temperature fluctuations penetrate only a few decimeters due to the extremely low thermal conductivity of the surface layers.
The relief of the lunar surface was mainly clarified as a result of many years of telescopic observations. "Moonsea", occupying about 40% of the visible surface of the moon, are flat lowlands, crossed by cracks and low winding trees; There are relatively few large craters on the seas. Many seas are surrounded by concentric ring ridges. The rest of the 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 the 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. Equatorial radius is equal to 3380 km. The average density of the planet is 3950 kg / m³. Mars has two moons - Phobos and Deimos.
Atmosphere.
The planet is shrouded in a gas envelope - an atmosphere that is less dense than the earth. Even in the deep depressions of Mars, where the pressure of the atmosphere is greatest, it is about 100 times less than at the surface of the Earth, and at the level of the Martian mountain peaks - 500-1000 times less. In composition, it resembles the atmosphere of Venus and contains 95.3% carbon dioxide mixed with 2.7% nitrogen, 1.6% argon, 0.07% carbon monoxide, 0.13% oxygen and about 0.03% water vapor, the content which changes, as well as impurities of neon, krypton, xenon.
The average temperature on Mars is much lower than on Earth at around -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 the frost can reach -125 ° C. Such sudden temperature drops are caused by the fact that the rarefied atmosphere of Mars is not capable of holding heat for a long time.
Above the surface of the planet often strong winds blow, the speed of which reaches 100 m / s. Low gravity allows even rarefied streams of air to lift huge clouds of dust. Sometimes quite large areas on Mars are covered by a grand dust storm. The global dust storm raged from September 1971 to January 1972, raising about a billion tons of dust to the atmosphere to a height of more than 10 km.
Water vapor in the atmosphere of Mars is quite a bit, but at low pressure and temperature, it is in a state close to saturation, and often gathers into clouds. Martian clouds are rather inexpressive in comparison with terrestrial ones, although they have various shapes and types: cirrus, undulating, leeward (near large mountains and under the slopes of large craters, in places protected from the wind). Over lowlands, canyons, valleys - and at the bottom of craters in the cold hours of the day there are often fogs.
As the pictures from the American landing stations Viking-1 and Viking-2 showed, the Martian sky has a pinkish color in clear weather, which is explained by the scattering of sunlight on specks and the backlighting of the smoke on the orange surface of the planet. In the absence of clouds, the gas envelope of Mars is much more transparent than the earth's, including for ultraviolet rays that are dangerous to living organisms.
Seasons.
Sunny day on Mars lasts 24 hours 39 minutes. 35 s A significant inclination of the equator to the orbital plane leads to the fact that in some parts of the orbit, the northern latitudes of Mars are illuminated and heated by the Sun, in others - the southern ones, that is, the seasons change. The Martian year lasts about 686.9 days. The change of seasons on Mars is the same as on Earth. Seasonal changes are most pronounced in the polar regions. In winter, the polar caps occupy a large area. The boundary of the north polar cap can move away from the pole at a third of the distance from the equator, and the boundary of the south cap overcomes half of this distance. Such a difference is caused by the fact that in the northern hemisphere, winter begins when Mars passes through the perihelion of its orbit, and in the southern hemisphere when it passes through aphelion. Because of this, winter is colder in the southern hemisphere than in the northern. The ellipticity of the Martian orbit leads to significant differences in the climate of the northern and southern hemispheres: in mid-latitudes, winter is colder and summer is warmer than in southern, but shorter than in northern .. When summer begins in the northern hemisphere of Mars, the polar polar cap decreases rapidly, but at this time another grows - near the south pole where winter comes. At the end of the 19th – beginning of the 20th century, the polar caps of Mars were believed to be glaciers and snow. According to modern data, both polar caps of the planet - northern and southern - are composed of solid carbon dioxide, i.e., dry ice, which forms when carbon dioxide freezes, which is part of the Martian atmosphere, and water ice mixed with mineral dust.
The structure of the planet.
Due to the low mass, 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 density distribution in the planet. The core may have a radius of up to half the radius of the planet. Apparently, it consists of pure iron or from an alloy of Fe-FeS (iron-iron sulfide) and, possibly, hydrogen dissolved in them. Apparently, the core of Mars is partially or completely in the liquid state.
Mars should have a powerful crust 70-100 km thick. Between the core and the crust is a silicate mantle enriched in iron. The red iron oxides present in the surface rocks determine the color of the planet. Now Mars continues to cool.
The seismic activity of the planet is weak.
Surface.
The surface of Mars, at first glance, resembles the moon. However, in fact, its relief is very diverse. Throughout the long geological history of Mars, volcanic eruptions and marshokes have changed its surface. Deep scars on the face of the god of war left meteorites, wind, water and ice.
The surface of the planet consists of two contrasting parts: the ancient highlands, covering the southern hemisphere, and the younger plains, concentrated in northern latitudes. In addition, there are two large volcanic areas - Elysium and Farsida. The difference in altitude between mountain and plain areas reaches 6 km. Why different areas are so different from each other is still unclear. Perhaps this division is associated with a very long-term catastrophe - the fall of a large asteroid on Mars.
The high-altitude part retained traces of active meteorite bombardment, which took place about 4 billion years ago. Meteorite craters cover 2/3 of the planet’s surface. In the old highlands there are almost as many of them as on the moon. But many Martian craters, due to weathering, managed to “lose their shape”. Some of them, apparently, were once washed away by streams of water. The northern plains look completely different. 4 billion years ago there were a lot of meteor craters on them, but then the catastrophic event, which was already mentioned, erased them from 1/3 of the surface of the planet and its relief in this area began to form anew. Some meteorites fell there and later, but in general there are few impact craters in the north.
The appearance of this hemisphere is determined by volcanic activity. Some of the plains are completely covered with ancient igneous rocks. Flows of liquid lava spread over the surface, froze, new streams flowed along them. These petrified "rivers" are concentrated around large volcanoes. At the end of lava languages, structures similar to terrestrial sedimentary rocks are observed. Probably, when the red-hot igneous masses melted layers of underground ice, rather extensive reservoirs formed on the surface of Mars, which gradually dried out. The interaction of lava and underground ice also led to the appearance of numerous furrows and cracks. Far from the volcanoes in the lowlands of the northern hemisphere, sand dunes stretch. Especially a lot of them at the north polar cap.
The abundance of volcanic landscapes suggests that in the distant past, Mars experienced a rather turbulent geological epoch, most likely it ended about a billion years ago. The most active processes occurred in the areas of Elysium and Farsida. At one time, they were literally squeezed out of the depths of Mars and now rise above its surface in the form of tremendous swellings: Elysium 5 km high, Farsid - 10 km. Numerous faults, cracks, ridges are concentrated around these blisters - traces of long-standing processes in the Martian crust. The most grandiose system of canyons several kilometers deep - the valley of Mariner - begins at the top of the Farsis 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 the atmosphere of Mars was denser, water could flow into the canyons, creating deep lakes in them.
The volcanoes of Mars are exceptional by earthly standards. But even among them, the Olympus Volcano stands out, located in the north-west of the Farsida Mountains. The diameter of the base of this mountain reaches 550 km, and its height is 27 km, i.e. it is three times the summit of Everest, the highest peak of the Earth. Olympus is crowned with a huge 60-km crater. To the east of the highest part of the mountains Farsida discovered another volcano - Alba. Although he can not compete with Olympus in height, the diameter of its base is almost three times larger.
These volcanic cones resulted from the calm outpourings of very liquid lava, similar in composition to the lava of terrestrial volcanoes of the Hawaiian Islands. Traces of volcanic ash on the slopes of other mountains suggest that sometimes catastrophic eruptions occurred on Mars.
In the past, running water played a huge role in the formation of the Martian relief. In the early stages of the study, Mars was presented to astronomers as a desert and anhydrous planet, but when Mars was able to photograph the surface from close range, it turned out that in the old highlands often there are seemingly abandoned scour water. Some of them look as if many years ago they were pierced by stormy, impetuous streams. Sometimes they stretch for many hundreds of kilometers. Some of these "streams" have a rather respectful age. Other valleys are very similar to the channels of calm earthly rivers. Their appearance is likely to be due 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 of the American astronomer Asaf Hall. Such satellites received names from Greek mythology: Phobos and Deimos - the sons of Ares (Mars) and Aphrodite (Venus), always accompanied their father. Translated from the Greek, “phobos” means “fear”, and “deimos” means “horror”.
Phobos. Deimos.
Both satellites of Mars are moving almost exactly in the equatorial plane of the planet. Using spacecraft, it was established that Phobos and Deimos are irregularly shaped and, in their orbital position, remain always turned to the planet by the same side. The size of Phobos is about 27 km, and Deimos - about 15 km. The surface of the moons of Mars consists of very dark minerals and is covered with numerous craters. One of them - Phobos has a diameter of about 5.3 km. Craters are probably born of meteorite bombardment, the origin of the system of parallel furrows is unknown. The angular velocity of the orbital motion of Phobos is so great that it, overtaking the axial rotation of the planet, rises, unlike other luminaries, in the west, and sets in the east.
The search for life on Mars.
For a long time Mars has been searching for forms of extraterrestrial life. In the study of the planet by the spacecraft of the Viking series, 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 the determination of photosynthesis with carbon, the label decomposition experiment was based on the assumption of the need for water to exist, and the gas exchange experiment took into account that Martian life should use water as a solvent. Although all three biological experiments gave a positive result, they are likely to have a non-biological 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 of the entire planetary system, if nothing unexpected happens, seems clear. The probability that the established order of motion of the planets will be disturbed by some wandering star is small, even for several billion years. In the near future, one does not have to expect strong changes in the energy flow of the Sun. Probably, glacial periods may repeat. A person is able to change the climate, but it may make a mistake. Continents in subsequent periods will rise and fall, but we hope that the processes will be slow. Massive meteorites may fall from time to time.
But basically the solar system will retain its modern look.
Plan.
1. Introduction.
2. Mercury.
3. Venus.
6. Conclusion.
7. Literature.
Planet Mercury.
The surface of Mercury.
Planet Venus.
The surface of Venus.
Planet Earth.
Land surface.
The planet Mars.
Surface of mars.
Volcano olympus
The inner region of the solar system is inhabited by various bodies: large planets, their satellites, as well as small bodies - asteroids and comets. Since 2006, a new subgroup has been introduced in the group of planets - dwarf planet (dwarf planet), possessing the inner qualities of the planets (spheroidal form, geological activity), but due to low mass they are not able to dominate in the vicinity of their orbit. Now, the 8 most massive planets - from Mercury to Neptune - are decided to simply be called planets (planet), although, in a conversation, astronomers for unambiguity often call them "big 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 the region of the major planets, we see a clear division into two groups of 4 planets in each: the outer part of this region is occupied by the giant planets, and the inner part is by the much less massive terrestrial planets. A group of giants is also usually divided in half: the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune). In the group of terrestrial planets, the division into halves is also planned: Venus and Earth are extremely similar to each other in many physical parameters, while Mercury and Mars are an order of magnitude smaller by mass and almost devoid of atmosphere (even Mars has hundreds of times smaller than Earth). Mercury is almost absent).
It should be noted that among the two hundred satellites of the planets it is possible to distinguish at least 16 bodies with the internal properties of full-fledged planets. Often they exceed their size and mass of the planet-dwarfs, but they are controlled by gravity of much more massive bodies. We are talking about the Moon, Titan, Galilean satellites of Jupiter and the like. Therefore, it would be natural to introduce into the nomenclature of the Solar system a new group for such “subordinate” objects of planetary type, calling them “satellite planets”. But while this idea is under discussion.
Let's return to the terrestrial planets. Compared to giants, they are attractive because they have a solid surface on which space probes can land. Beginning in the 1970s, automatic stations and self-propelled apparatuses of the USSR and the USA repeatedly sat down and successfully worked on the surface of Venus and Mars. Landing on Mercury has not yet been, because flying in the vicinity of the Sun and landing on a massive non-atmospheric body are associated with major technical problems.
Studying terrestrial planets, astronomers do not forget about the Earth itself. The analysis of images from space made it possible to understand much in the dynamics of the earth's atmosphere, in the structure of its upper layers (where airplanes and even balloons do not rise), in the processes occurring in its magnetosphere. Comparing the structure of the atmospheres of earth-like planets among themselves, much can be understood in their history and more accurately predict their future. And since all higher plants and animals inhabit the surface of our (or not only our?) Planet, the characteristics of the lower layers of the atmosphere are especially important for us. This lecture is devoted to the planets of the Earth type; mainly their appearance and surface conditions.
The brightness of the planet. Albedo
Looking at the planet from afar, we easily distinguish bodies with and without atmosphere. The presence of the atmosphere, or rather 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 the planets are arranged in a row from completely cloudless (non-atmospheric) to fully closed clouds: Mercury, Mars, Earth, Venus. Stony non-atmospheric bodies resemble each other to almost complete indistinguishability: compare, for example, large-scale images of the Moon and Mercury. Even an experienced eye can hardly distinguish between the surfaces of these dark bodies, densely covered with meteorite craters. But the atmosphere gives any planet a unique look.
The presence or absence of the atmosphere of the planet is controlled by three factors: the temperature and the gravitational potential at the surface, as well as the global magnetic field. Only the Earth has such a field, and it essentially 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 the high temperature and the powerful solar wind. Mars, with almost the same gravity as that of Mercury, was able to preserve the remnants of the atmosphere, because due to its remoteness from the Sun it is cold and not so intensely blown by the solar wind.
In their physical parameters, Venus and Earth are almost twins. They have very similar size, mass, and hence the average density. Their internal structure should also be similar, - the crust, the mantle, the iron core - although there is no certainty about this yet, since there are no seismic and other geological data on the depths of Venus. Of course, we did not penetrate deeply into the bowels of the Earth: in most places at 3-4 km, at certain points at 7-9 km and only at one at 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 depth in great detail, but for other planets there is almost no such data. Detailed maps of the gravitational field obtained only for the moon; heat fluxes from the depths are measured only on the moon; seismometers so far also worked only on the moon and (not very sensitive) on mars.
Geologists still judge the internal life of the planets by the characteristics of their solid surface. For example, the absence of signs of lithospheric plates in Venus significantly distinguishes it from the Earth, in the evolution of whose surface tectonic processes (continental drift, spreading, subduction, etc.) play a decisive role. At the same time, some indirect data indicate the possibility of plate tectonics on Mars in the past, as well as tectonics of ice fields on Europe, the satellite 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 different from each other can exhibit similar geological phenomena.
Let us return to what is available to astronomers and other specialists for direct study, namely, to the surface of the planets or their cloud layer. In principle, the opacity of the atmosphere in the optical range is not an insurmountable obstacle to the study of the solid surface of the planet. Radiolocation from Earth and from space probes made it possible to study the surfaces of Venus and Titan through their non-transparent atmosphere light. However, these works are sporadic, and systematic studies of the planets are still carried out with optical instruments. And more importantly: the optical radiation of the sun is 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 light 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 droplets of concentrated sulfuric acid, which perfectly reflects light. Our Earth is not too dark either, since 30-40% of the Earth’s atmosphere is filled with water clouds, and they also diffuse and reflect light well. Here is a photo (fig. Above), where the Earth and the Moon simultaneously hit the frame. This image was taken by the Galileo space probe, flying past the Earth on its way to Jupiter. Look how much the moon is darker than the Earth and generally darker than any planet with an atmosphere. This is a general pattern - non-atmospheric bodies are very dark. The fact is that under the influence of cosmic radiation, any solid substance gradually darkens.
The assertion that the surface of the moon is dark usually puzzles: at first glance, the lunar disk looks very bright; On a cloudless night, he even blinds us. But this is only in contrast with an even darker night sky. To characterize the reflectivity of any body using a value called albedo. This is the degree of whiteness, that is, the coefficient of reflection of light. Albedo equal to zero - absolute blackness, full absorption of light. Albedo equal to one - full reflection. Physicists and astronomers have several different approaches to the definition of albedo. It is clear that the brightness of the 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 out has one value, the reflection coefficient, and the snow that you hit with a shoe will have a completely different value. And dependence on orientation is easy to demonstrate with a mirror, blowing solar bunnies.
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, mainly due to the clouds. A continuous cloud cover of Venus reflects 77% of the light. Our Moon is one of the darkest bodies, reflecting on average about 11% of the light; and its visible hemisphere due to the presence of vast dark “seas” reflects the light even worse - less than 7%. But there are even darker objects; for example, asteroid 253 Matilda with its albedo of 4%. On the other hand, there are surprisingly light bodies: Enceladus' satellite of Saturn reflects 81% of visible light, and its geometrical albedo is simply fantastic - 138%, that is, it is brighter than a perfectly white disk of the same section. It is even difficult to understand how he does it. Pure snow on the Earth reflects the light worse; What kind of snow lies on the surface of this small and pretty Enceladus?
Heat balance
The temperature of any body is determined by the balance between the influx of heat to it and its losses. There are three known heat exchange mechanisms — radiation, heat conduction, and convection. The last two of them require direct contact with the environment, so in the vacuum of space the most important and, in fact, the only mechanism that becomes the first is radiation. For designers of space technology, this creates considerable problems. They have to take into account several sources of heat: the Sun, the planet (especially in low orbits) and the internal units of the spacecraft itself. And for the discharge of heat there is only one way - radiation from the surface of the apparatus. To maintain the balance of heat fluxes, the designers of space technology regulate the effective apparatus albedo using screen-vacuum insulation and radiators. When such a system fails, conditions in a spacecraft can become quite uncomfortable, as the history of the Apollo 13 expedition to the Moon reminds us.
But for the first time, the creators of high-altitude balloons, the so-called stratostats, encountered this problem in the first third of the 20th century. In those years, they still did not know how to create complex thermal control systems of a hermetic nacelle, therefore they limited themselves to simple selection of the albedo of its external surface. How sensitive the temperature of the body to its albedo, says the story of the first flights to the stratosphere.
The gondola of his stratostat FNRS-1 Swiss Auguste Picard painted on one side in white, and on the other - in black. The idea was to regulate the temperature in the gondola by turning the sphere with one side or the other to the Sun. For rotation outside set the propeller. But the device did not work, the sun was shining from the "black" side and the internal temperature in the first flight rose to 38 ° C. In the next flight, the entire capsule was simply covered with silver to reflect the sun's rays. Inside it was –16 ° C.
American stratostat designers Explorer they took into account the experience of Picard and accepted a compromise: 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 quite good, but also not ideal: during flights in the capsule it was 5 ° C.
Soviet strataauts simply insulated aluminum capsules with a layer of felt. As practice has shown, this solution was the most successful. The internal heat, mainly emitted by the crew, was sufficient to maintain a stable temperature.
But if the planet does not have its own powerful sources of heat, 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, maintaining the water cycle in nature due to it, storing it as a result of photosynthesis in biomass, oil, coal, and gas. The moon absorbs almost all sunlight, foolishly turning it into high-entropy infrared radiation and thereby maintaining its rather high temperature. But Enceladus, with its perfectly white surface, proudly pushes away almost all sunlight from itself, for which it pays with a monstrously low surface temperature: on average around –200 ° C, and in some places to –240 ° C. However, this satellite - “all in white” - does not suffer much from external cold, since it has an alternative source of energy - the tidal gravitational influence of its neighbor-Saturn (), supporting its under-ice ocean in a liquid state. But for terrestrial planets, internal heat sources are very weak, 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 radiation energy that has passed through atmosphere to the surface of the planet.
Greenhouse effect and the climate of the planet
Depending on how far the planet is from the Sun and how much of the sun it absorbs, temperature conditions on the surface of the planet and its climate are formed. What is the spectrum of any self-luminous body, for example, a star? In most cases, the spectrum of a star is “one-humped”, almost Planck, a curve in which the position of the maximum depends on the temperature of the surface of the star. Unlike a star, the spectrum of the planet has two “humps”: it reflects part of the starlight in the optical range, and absorbs and re-emits the other part in the infrared range. The relative area under these two humps is determined by the degree of reflection of light, that is, albedo.
Let's look at the two closest planets 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 farther from the Sun than Mercury; per unit of its cloudy surface falls 3.4 times less than sunlight. Given the difference in albedo, every square meter of solid surface of Mercury receives almost 16 times more solar heat than the same surface on Venus. And, nevertheless, on the whole solid surface of Venus, hellish conditions are a huge temperature (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 daytime the surface of Mercury heats up to 430 ° C, and at night it cools to –170 ° C. But already at a depth of 1.5-2 meters daily fluctuations smooth 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, it is generally room temperature.
What is the matter? Why is Mercury close to the Sun and readily absorbing its rays, is heated to room temperature, and Venus, farther from the Sun and actively reflecting its rays, is heated like a furnace? How to explain this physics?
The atmosphere of the Earth is almost transparent: it transmits 80% of the incoming sunlight. Air cannot escape into space as a result of convection - the planet does not release it. It means that it can be cooled only in the form of infrared radiation. And if the IR radiation remains locked, then it heats the 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 most of it returns to the surface of the Earth and heats it until thermodynamic equilibrium is established. And how is it installed?
The temperature rises, and the maximum in the spectrum shifts (the law of Wine) until it finds in the atmosphere a “transparency window” through which the IR rays go into space. The balance of heat fluxes is established, but at a higher temperature than it could be without an atmosphere. This is the greenhouse effect.
In our lives, we often face the greenhouse effect. And not only in the form of a garden greenhouse or a pan set on the stove, which we cover with a lid to reduce heat transfer and speed up boiling. Just these examples do not demonstrate a pure greenhouse effect, since they reduce both radiant and convective heat removal. Much closer to the described effect is an example of a clear frosty night. With dry air and a cloudless sky (for example, in the desert), after sunset, the earth cools rapidly, and moist air and clouds smooth out daily variations in temperature. Unfortunately, this effect is well known to astronomers: clear starry nights are especially cold, which makes the telescope work very uncomfortable. Returning to the figure above, we will see the reason: it is the water vapor in the atmosphere that serves as the main obstacle to the heat-carrying infrared radiation.
The moon has no atmosphere, and therefore there is no greenhouse effect. On its surface, thermodynamic equilibrium is established in an explicit form, there is no exchange of radiation between the atmosphere and a solid surface. Mars has a rarefied atmosphere, but still its greenhouse effect adds its 8 ° C. And he adds almost 40 ° C to Earth. If our planet did not have such a dense atmosphere, the temperature of the Earth would be 40 ° C lower. Today, it averages 15 ° C around the globe, and it would be –25 ° C. All the oceans would freeze, the surface of the Earth would become white from the snow, the albedo would rise, and the temperature would fall even lower. In general - a terrible thing! But it is good that the greenhouse effect in our atmosphere works and warms us. And much more he works on Venus - more than 500 degrees raises the average temperature of Venus.
Surface of the planets
So far, we have not embarked on a detailed study of other planets, mainly limited to the observation of their surface. And how important is the information on the appearance of the planet for science? What valuable can tell us the image of its surface? 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, and tomorrow will be different, or not tomorrow, but after 1000 years, that 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 they only tell us about some of the general properties of the modern dynamics of their atmospheres. Looking at these planets, our descendants will see a completely different picture, and we will never know what picture our ancestors could see. Thus, looking from the side to planets with a dense atmosphere, we cannot judge their past, since we only see a changeable cloud layer. It is quite another thing - the Moon or Mercury, whose surfaces store traces of meteorite bombardments and geological processes that have occurred over the past billions of years.
And such bombardments of giant planets leave practically no traces. One of these events occurred at the end of the twentieth century right in front of astronomers. We are talking about the comet Shoemaker-Levi-9. In 1993, a strange chain of two dozen small comets was noticed near Jupiter. The calculation showed that these are fragments of a single comet that flew near Jupiter in 1992 and was torn apart by the tidal effect of its powerful gravitational field. The astronomers did not see the episode of the comet's collapse, and only the moment when the train's line of cometary fragments was removed from Jupiter was caught. If there were no decay, the comet, having flown to Jupiter along a hyperbolic trajectory, would have gone off into the distance along the second branch of the hyperbola and most likely would never have come closer to Jupiter. But the body of the comet did not withstand the tidal stress and collapsed, and the expenditure of energy on the deformation and rupture of the body of the comet reduced the kinetic energy of its orbital motion, transferring fragments from a hyperbolic orbit to an elliptical one, closed around Jupiter. The distance of the orbit in the pericenter was less than the radius of Jupiter, and the fragments in 1994 crashed into the planet one by one.
The incident was grand. Each "fragment" of the cometary nucleus is an ice block of 1 × 1.5 km in size. They in turn flew into the atmosphere of a giant planet at a speed of 60 km / s (the second cosmic 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 with great interest, being safe on Earth, observed a cosmic catastrophe on Jupiter. Unfortunately, the fragments of a comet beat into Jupiter from the side that was not at that moment visible from Earth. Fortunately, it was at this time that the Galileo space probe was on its way to Jupiter, he saw these episodes and showed them to us. Due to the fast daily rotation of Jupiter, the collision areas became accessible within a few hours to ground-based telescopes and, which is especially valuable, near-earth, such as the Hubble Space Telescope. This was very useful, since every lump, crashing into the atmosphere of Jupiter, caused a huge explosion, destroying the upper cloud layer and creating for some time a window of visibility deep into the Jovian atmosphere. So, thanks to the comet bombardment, we were able to look there for a while. But 2 months passed and no traces remained on the cloudy surface: the clouds tightened all the windows, as if nothing had happened.
Another thing Land. On our planet, meteor scars remain for a long time. Before you is the most popular meteor 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 methods. They are not visible from above.
By the way, there is a fairly reliable ratio between the size of a large meteorite falling to Earth and the diameter of a crater formed by it - 1:20. A kilometer 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” struck the Earth — even kilometer and even ten kilometers. We know today about 200 large craters; they are called astroblemes (celestial wounds); and every year discover a few new ones. The largest diameter of 300 km is found in southern Africa, its age is about 2 billion years. In Russia, the largest crater Popigay in Yakutia with a diameter of 100 km. Surely there are larger ones, for example, at the bottom of the oceans, where they are harder to notice. True, the ocean floor in the geological sense is younger than the continents, but it seems that in the Antarctic there is a crater 500 km in diameter. It is under water and only the bottom profile indicates its presence.
On a surface The moonwhere there is neither wind nor 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 space bombardment. On the reverse side is an even more useful picture for science. It seems that for some reason there never fell especially large bodies, or, falling, they could not break through the lunar crust, which is twice as thick on the back side than on the visible one. Therefore, the escaping lava did not fill the large craters and did not hide the historical details. On any piece of the lunar surface there is a meteor crater, large or small, and there are so many of them that the younger ones destroy those that were formed earlier. Saturation has happened: the Moon can no longer become more klenitsirovanny than it is. Craters everywhere. And this is a wonderful chronicle of the history of the solar system. According to it, several episodes of active crater formation were identified, including the era of heavy meteorite bombardment (4.1–3.8 billion years ago), which left traces on the surface of all Earth-like planets and many satellites. Why streams of meteorites hit the planets in that era, we still have to understand. We need new data on the structure of the lunar interior and on the composition of the substance at different depths, and not only on the surface from which samples have been collected so far.
Mercury outwardly similar to the moon, because, like her, devoid of atmosphere. Its stony surface, not subject to gas and water erosion, for a long time retains traces of meteorite bombardment. Among the terrestrial planets, Mercury has the oldest geological traces around 4 billion years old. But on the surface of Mercury there are no large seas filled with dark, frozen lava and similar to the lunar seas, although there are no less 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 larger than the Moon. The fact is that the Moon is almost entirely a stony body, whereas Mercury has a huge metallic core, apparently consisting mainly of iron and nickel. The radius of its metal core is about 75% of the radius of the planet (and the Earth has only 55%). The volume of the metallic core of Mercury is 45% of the volume of the planet (and the Earth has only 17%). Therefore, the average density of Mercury (5.4 g / cm 3) is almost equal to the average density of the Earth (5.5 g / cm 3) and significantly exceeds the average density of the Moon (3.3 g / cm 3). Having a large metal core, Mercury could surpass the Earth by its average density, if it were not for the small force of gravity on its surface. Having a mass of only 5.5% of the earth, it has almost three times less gravity, which is not able to compact its bowels so much as the bowels of the Earth have condensed, in which even the silicate mantle has a density of about (5 g / cm 3).
Mercury is difficult to explore as it moves close to the Sun. In order to launch an interplanetary spacecraft from Earth, it must be strongly braked, that is, accelerated in the direction opposite to the Earth’s orbital motion; only then will it begin to "fall" towards the sun. It’s impossible to do it right away with a rocket Therefore, in the two flights so far carried out to Mercury, gravitational maneuvers were used in the field of the Earth, Venus and Mercury itself, to decelerate the space probe and transfer it into the orbit of Mercury.
For the first time, Meriner 10 (NASA) went to Mercury in 1973. He first became close to Venus, slowed down in its gravitational field and then passed three times near Mercury in 1974-75. Since all three meetings occurred in the same region of the orbit of the planet, and its daily rotation is synchronized with the orbital, all three times the probe photographed the same hemisphere of Mercury, illuminated by the Sun.
Over the next few decades, flights to Mercury was not. And only in 2004 was it possible to launch the second unit - 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 went into orbit around Mercury in 2011 and conducted research of the planet for 4 years.
Work 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 sunlight there is almost 7 times more. Without a special “sun umbrella”, the electronic filling of the probe would overheat. The third expedition to Mercury is being prepared. BepiColomboEuropeans and Japanese participate in it. The launch is scheduled for autumn 2018. Two probes will fly at once, which will go into orbit around Mercury at the end of 2025 after a flight near the 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 is planned of the magnetosphere and the magnetic field of Mercury, which is a mystery to scientists. Although Mercury rotates very slowly, and its metal core had to cool down and solidify for a long time, the planet has a dipole magnetic field that is 100 times less intense than Earth's, but still supports the magnetosphere around the planet. The modern theory of the generation of magnetic fields in celestial bodies, the so-called theory of turbulent dynamo, requires a layer of liquid conductor of electricity in the interior of the planet (on Earth, this is the outer part of the iron core) and relatively fast rotation. For whatever reason, the core of Mercury is still liquid until it is clear.
Mercury has an amazing feature that no other planet has anymore. The motion of Mercury in orbit around the Sun and its rotation around its axis are clearly synchronized with each other: during two orbital periods, it makes three turns around the axis. Generally speaking, astronomers have known each other for a long time: our Moon rotates synchronously around an axis and revolves around the Earth, the periods of these two movements are the same, that is, they are in a 1: 1 ratio. And on other planets, some satellites demonstrate the same feature. This is the result of the tidal effect.
To follow the movement of Mercury (fig. Above), put an arrow on its surface. It can be seen that in one revolution around the Sun, i.e. in one Mercurian year, the planet turned around exactly one and a half times around the axis. During this time, the day in the area of the arrow was replaced at night, half of the sunny days passed. Another one-year turnaround - and in the area of the arrow the day comes again, one sunny day has elapsed. Thus, on a Mercury sunny day lasts two Mercurian years.
We will talk in detail about the tides in ch. 6. It was precisely as a result of the tidal influence from the side of the Earth that the Moon synchronized two of its movements - axial rotation and orbital circulation. The Earth has a strong influence on the moon: it stretched out its shape, stabilized the 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 (the degree of this “almost” we discussed in Chapter 1). Therefore, the tidal effect varies only slightly and controls the rotation of the moon along the entire orbit, leading to a 1: 1 resonance.
Unlike the Moon, Mercury moves around the Sun in a substantially elliptical orbit, now approaching the star, now moving away from it. When it is far away, in the aphelion region of the orbit, the tidal influence of the Sun weakens as it depends on the distance like 1 / R 3 When Mercury approaches the Sun, the tides are much stronger, so only in the perihelion region does Mercury synchronize two of its movements effectively — diurnal and orbital. The second Kepler law tells us that the angular velocity of the orbital motion is maximal at the point of perihelion. It is there that the "tidal capture" and the synchronization of the angular velocities of Mercury - diurnal and orbital occurs. At the point of perihelion, they are exactly equal to each other. Moving further, Mercury almost ceases to feel the tidal influence of the Sun and retains its angular velocity of rotation, gradually reducing the angular velocity of the orbital motion. Therefore, in one orbital period, he manages to make one and a half daily turnover 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 pictures of Mercury appeared, showed them to each other and asked: "Well, guess what, is it the Moon or the Mercury?" Guess is really difficult. And there, and there surface beaten by meteorites. But the features, of course, are. Although there are no large lava seas on Mercury, its surface is not uniform: there are areas older and younger (the basis for this is the counting of meteorite craters). Mercury differs from the Moon by the presence of characteristic ledges and folds on the surface, which arose as a result of the compression of the planet during the cooling of its huge metal core.
Temperature drops on the surface of Mercury are greater than on the moon. In the daytime at the equator 430 ° C, and at night –173 ° C. But the ground of Mercury serves as a good heat insulator, so at a depth of about 1 m the daily (or biennial?) Temperature drops are no longer felt. So, if you arrive at Mercury, then the first thing to do is dig a dugout. It will be around 70 ° C at the equator; it's hot. But in the area of geographic poles in the dugout will be around –70 ° C. So you can easily find the geographical latitude in which in the dugout you will be comfortable.
The lowest temperatures are observed at the bottom of polar craters, where I never get the sun's rays. It was there that discovered deposits of water ice, which were previously groped by radars from the Earth, and then confirmed by the instruments of the MESSENGER space probe. The origin of this ice is still under discussion. 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 - the Heat Plain ( Caloris basin) with a diameter of 1,550 km. This is a trail from the impact of an asteroid with a diameter of at least 100 km, which nearly split a small planet. It happened about 3.8 billion years ago, during the so-called "late heavy bombardment" ( Late Heavy Bombardment), when the number of asteroids and comets in orbits crossing the orbits of the terrestrial planets has increased for reasons that are not fully understood.
When in 1974 Mariner 10 photographed the Heat Plain, we did not know what happened on the opposite side of Mercury after this terrible blow. It is clear that if they hit the ball, sound and surface waves are excited, which propagate symmetrically, pass through the "equator" and gather at an antipodal point diametrically opposite to the point of impact. The disturbance there is tightened to a point, and the amplitude of seismic oscillations is rapidly increasing. This is similar to how cattle drovers click their whips: the energy and momentum of the wave are almost preserved, and the thickness of the whip tends to zero, so the speed of oscillation increases and becomes supersonic. It was expected that in the area of Mercury opposite the basin Caloris there will be a picture of incredible destruction. In general, it almost turned out to be there: there was a vast hilly area with a grooved surface, although I expected that there would be a crater-antipode. It seemed to me that when a seismic wave collapsed, the phenomenon of a “mirror” fall of an asteroid would occur. We observe this when a drop falls on a calm water surface: first, it creates a small depression, and then the water rushes back and throws a small new drop upwards. This did not happen on Mercury, and we now understand why. Its subsoil turned out to be non-uniform and the exact 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 the Mercury craters are not so high. The likely reason for this is greater gravity and warmer and softer bowels of Mercury.
Venus - the second planet from the Sun and the most mysterious of the terrestrial planets. It is not clear what is the origin of its very dense atmosphere, almost entirely composed of carbon dioxide (96.5%) and nitrogen (3.5%) and causing a powerful greenhouse effect. It is not clear why Venus rotates so slowly around the 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 terrestrial days. This phenomenon is called the superrotation of the atmosphere. At the same time, the atmosphere rubs against the surface of the planet and would have to slow down for a long time. After all, she can not move for a long time around the planet, whose solid body practically stands still. But the atmosphere rotates, and even in the opposite direction of the rotation of the planet itself. It is clear that the energy of the atmosphere is dissipated from friction against the surface, and its angular momentum is transmitted to the body of the planet. So, there is an influx of energy (obviously - solar), due to which the heat engine is working. 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, Coriolis forces on it are weaker than on Earth, therefore atmospheric cyclones are less compact there. In fact, there are only two: one in the northern hemisphere, the other in the southern. Each of them "wound" from the equator to its pole.
The upper layers of the Venusian atmosphere investigated in detail the passage (carrying out a gravity maneuver) and orbital probes — American, Soviet, European, and Japanese. Over the course of several decades, Soviet engineers launched the “Venus” series of vehicles there, and this was our most successful breakthrough in the field of exploration of the planets. The main task was to land a descent vehicle on the surface in order to see what was 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, represented Venus as inhospitable (hot, swampy, with a poisonous atmosphere), but on the whole a Earth-like world. For the same reason, the first landing gears of the Venusian probes did not very strong, not able to resist a lot of pressure. And they died, descending in the atmosphere, one after another. Then their bodies began to make stronger, designed for a pressure of 20 atmospheres. But this was not enough. Then the designers, "biting the bit," made a titanium probe that can withstand a pressure of 180 atm. And he safely sat on the surface ("Venus-7", 1970). Note that not every submarine can withstand such pressure prevailing at a depth of about 2 km in the ocean. It turned out that at the surface of Venus the pressure does not fall below 92 atm (9.3 MPa, 93 bar), and the temperature is 464 ° C.
With the dream of a hospitable Venus, similar to the Earth of the Carboniferous period, it was finally ended in 1970. For the first time, the apparatus designed for such hellish conditions (“Venera-8”) successfully descended and worked on the surface in 1972. From this point of landing it was a routine operation on the surface of Venus, but it didn’t 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 at Venus in 1975 (“Venus-9 and -10”). In general, the work on the Venus-9 ... -14 descent vehicles (1975–1981), which studied both the atmosphere and the surface of the planet at the landing site, which even managed to take soil samples and determine its chemical composition and mechanical properties. But the greatest effect among fans of astronomy and astronautics caused the photo-panoramas of the landing sites they transmitted, first black and white, and later color. By the way, the Venusian sky, when viewed from the surface, is orange. Handsomely! Until now (2017), these pictures remain the only ones and arouse great interest among planetary scientists. They continue to process them and from time to time find new parts on them.
A significant contribution to the study of Venus in those years was made by the American space program. Mariner-5 and -10 flying devices studied the upper atmosphere. Pioneer Venus 1 (1978) became the first American satellite of Venus and conducted radar measurements. A "Pioneer Venus-2" (1978) sent 4 descent vehicles into the atmosphere of the planet: one large (315 kg) with a parachute to the equatorial region of the daytime hemisphere and three small ones (90 kg each) without parachutes - to medium latitudes and north of the daytime hemisphere, as well as the night hemisphere. None of them was designed to work on the surface, but one of the small vehicles landed safely (without a parachute!) And worked on the surface for more than an hour. This case allows you to feel how great the density of the atmosphere is at 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 terrestrial air and only 15 times less than the density of liquid water.
It was very difficult to create strong scientific probes that withstand the pressure of the Venusian atmosphere, the same as at a kilometer depth in our oceans. But it was even more difficult to make them resist the surrounding temperature of 464 ° C with such dense air. Heat flow through the body is colossal. Therefore, even the most reliable devices worked no more than two hours. In order to quickly sink to the surface and extend their work there, the Venus dropped a parachute during landing and continued descending, being slowed down only by a small shield on its hull. The impact on the surface was softened by a special damping device - the landing support. The design was so successful that the Venera-9 sat down on a slope with a slope of 35 ° without any problems and worked normally.
Given the high albedo of Venus and the colossal density of its atmosphere, scientists doubted that the surface would have enough sunlight to photograph. In addition, at the bottom of the gas ocean of Venus, a dense fog could easily hang, scattering sunlight and not allowing a contrast image to be obtained. Therefore, halogen mercury lamps were installed on the first planting machines to illuminate the soil and create light contrast. But it turned out that natural light is quite enough there: on Venus it is as bright as an overcast day on Earth. And the contrast in natural light is also quite acceptable.
In October 1975, the landing gears Venera-9 and -10, through their orbital blocks, transmitted to Earth the first ever photographs of the surface of another planet (if we ignore the Moon). At first glance, the perspective on these panoramas looks strangely distorted: the reason is the turn of the shooting direction. These images were obtained by a photophotometer (an optical-mechanical scanner), whose “look” slowly moved from the horizon under the legs of the landing gear and then to another horizon: a 180 ° scan was obtained. Two telephotometers on opposite sides of the apparatus were to give a full panorama. But the lens caps did not always open. For example, on the Venus-11 and -12, none of the four has opened.
One of the most beautiful experiments on the study of Venus was carried out using probes "VeGa-1 and -2" (1985). Their name stands for “Venus-Halley”, because after the separation of the descent vehicles aimed at the surface of Venus, the flight parts of the probes went to investigate the nucleus of Halley’s comet and did it for the first time. The landing gears were also not quite ordinary: the main part of the apparatus was landing on the surface, and during descent the balloon made by French engineers was separated from it and flew in Venus atmosphere at an altitude of 53-55 km for two days, transmitting to Earth data on temperature, pressure , light and visibility in the clouds. Due to the powerful wind blowing at this altitude at a speed of 250 km / h, the balloons managed to fly around a large part of the planet. Handsomely!
The photographs from the landing sites show only small areas of the Venusian surface. Is it possible to see the whole Venus through the clouds? Can! Radar sees through the clouds. Two Soviet satellites with side-looking radars and one American flew to Venus. According to their observations, the radio maps of Venus were drawn up with a very high resolution. It is difficult to demonstrate on the general map, but it is clearly visible on separate map fragments. The levels on the radio maps are shown: blue and blue are lowlands; if Venus had water, it would be oceans. But liquid water on Venus cannot exist. And there is practically no gaseous water either. Greenish and yellowish are continents, let's call them that. Red and white are the highest points on Venus. This “Venus Tibet” is the highest plateau. The highest peak on it - Mount Maxwell - rises 11 km.
There are no reliable facts about the depths of Venus, its internal structure, since seismic studies have not yet been conducted there. In addition, the slow rotation of the planet does not allow to measure its moment of inertia, which could tell about the density distribution 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 lack of water on it, which on Earth serves as a “lubricant”, allowing the plates to slide and dive under each other. Together with the high temperature of the surface, this leads to a slowing down or even complete absence of convection in the body of Venus, reduces the cooling rate of its depths and can explain its lack of a magnetic field. All this looks logical, but requires experimental verification.
By the way, oh 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 on the basis of school knowledge. But in connection with the study of other planets, I note that the depths of our planet are also not completely understood. Almost every year major discoveries in geology take place, sometimes even new layers are found in the bowels of the Earth. We do not even know the exact temperature in the core of our planet. See recent reviews: some authors believe that the temperature at the boundary of the inner core is about 5000 K, and others say that more than 6,300 K. These are the results of theoretical calculations that include not quite reliable parameters describing the properties of a substance at a temperature of thousands of kelvins and pressure millions of bars. Until these properties are reliably studied in the laboratory, we will not get accurate knowledge of the Earth’s interior.
The uniqueness of the Earth among planets similar to it consists 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 from the solar wind and, indirectly, the hydrosphere. To generate a magnetic field, as it now seems, there must be a liquid electrically conductive layer in the bowels of the planet, covered by convective motion, and a fast daily rotation, providing Coriolis force. Only under these conditions, the dynamo-mechanism that amplifies the magnetic field is activated. Venus practically does not rotate, so it does not have a magnetic field. The iron core of small Mars has long been cooled and hardened, so it is also devoid of a magnetic field. It would seem that Mercury rotates very slowly and should have cooled down earlier than Mars, but it has a quite tangible dipole magnetic field with a intensity that is 100 times weaker than the earth's one. Paradox! The tidal influence of the Sun is now considered responsible for maintaining the iron core of Mercury in the 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 solid planet with a magnetic field will remain, oddly enough, Mercury.
And now we turn to Mars. Its appearance immediately attracts us for two reasons: even in photographs taken from afar, white polar caps and a translucent atmosphere are visible. This is a relative of Mars with the Earth: the polar caps give rise to the thought of the presence of water, and the atmosphere gives rise to the possibility of breathing. And although on Mars with water and air, not everything is as good as it seems at first glance, this planet has long attracted researchers.
Earlier, astronomers studied Mars through a telescope, and therefore were looking forward to moments called “Mars confrontations”. What is opposed to in these moments?
From the point of view of the earth observer, at the moment of the opposition Mars is on one side of the Earth, and the Sun is on the other. It is clear that at these moments the Earth and Mars approach the minimum distance, Mars is visible in the sky all night and is well lit by the Sun. Earth makes its revolution around the Sun for the year, and Mars - for 1.88 years, so the average time interval between the oppositions takes a little more than two years. The last confrontation of Mars was in 2016, however, it was not particularly close. Mars’s orbit is noticeably elliptical, so the Earth’s closest approach to it happens when Mars is in 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 every 15–17 years, our planets approach less than 60 million km. This will be in 2018. And the super-friendly standoff took place in 2003: then, there was only 55.8 million km from Mars. In connection with this, a new term was born - “the greatest oppositions of Mars”: these are now considered to be rapprochements of less than 56 million km. They occur 1-2 times per century, but in this century there will even be three of them - wait for 2050 and 2082.
But even at the moments of great confrontations with a telescope from Earth, little is visible on Mars. Here is a drawing of an astronomer who looks at Mars through a telescope. An unprepared person will look and be disappointed - he will not see anything at all, only a small pink “drop”. But in the same telescope the astronomer's experienced eye sees more. Astronomers noticed the polar cap long ago, centuries ago. And also - dark and light areas. Dark traditionally called the seas, and light - the continents.
Increased interest in Mars arose in the era of the great opposition of 1877: - by that time, good telescopes had already been built, and astronomers made several important discoveries. The American astronomer Asaf Hall discovered the moons of Mars, Phobos and Deimos. And the Italian astronomer Giovanni Schiaparelli sketched mysterious lines on the surface of the planet - the Martian canals. Of course, Schiaparelli was not the first to see the channels: some of them noticed before him (for example, Angelo Secchi). But after Schiaparelli, this topic has become dominant in the study of Mars for many years.
Observations of the details of the surface of Mars, such as the "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 had to be given a name, Schiaparelli called them "canals" (canali), meaning by this the sea straits, and not man-made structures. He believed that water actually flows through these channels in the polar regions during the period of melting of the polar caps. After the discovery of "channels" on Mars, some scientists suggested their artificial nature, which was the basis for the hypotheses about the existence of intelligent beings on Mars. But Schiaparelli himself did not consider this hypothesis to be scientifically based, although he did not rule out the existence of life on Mars, perhaps even reasonable.
However, the idea of an artificial system of irrigation canals on Mars began to strengthen in other countries. This was partly due to the fact that the Italian canali was presented in English as canal (man-made waterway), and not as a channel (natural sea channel). Yes, and in Russian the word "channel" implies an artificial structure. The idea of the Martians then attracted many, and not only writers (remember HG 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 a scion of a well-born family, he would rather become a diplomat, a writer or a traveler than an astronomer. However, after reading Schiaparelli's works on the canals, he became interested in Mars and believed in the existence of life and civilization on it. In general, he abandoned all other business and began studying the Red Planet.
With the money of his wealthy family, Lovell built an observatory and began drawing canals. Note that the photo was then in its infancy, and the eye of an experienced observer is able to notice the smallest details in the conditions of atmospheric turbulence, distorting the images of distant objects. Maps of the Martian canals created at the Lovell Observatory were the most detailed. Besides, being a good writer, Lovell wrote several entertaining books - Mars and its canals (1906), Mars as the abode of life (1908) and others. Only one of them was translated into Russian before the revolution: “Mars and life on it” (Odessa: Matezis, 1912). These books captivated an entire generation of hope to meet the Martians.
It should be recognized that the story of the Martian channels has not received an exhaustive explanation. There are old drawings with channels and modern photos - without them. Where are the channels? What was it? Astronomers conspiracy? Mass insanity? Self suggestion? It is difficult to blame the scientists who gave their lives to science. Perhaps the clue to this story awaits us ahead.
And today we study Mars, as a rule, not with 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 advantageous semi-elliptical trajectory. With the help of the Third Law of Kepler, it is easy to calculate the duration of such a flight. Due to the large 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.
Can a manned expedition be sent to Mars? This is a big and interesting topic. It would seem that this requires only a powerful booster and a convenient spacecraft. No one has a sufficiently powerful carrier, but American, Russian and Chinese engineers are working on them. There is no doubt that such a rocket in the coming years will be created by state-owned enterprises (for example, our new Angara rocket in its most powerful form) or by private companies (Ilon Musk - why not).
Is there a ship in which astronauts spend many months on their way to Mars? There is no such thing yet. All existing (Union, Shenzhou) and even passing tests (Dragon V2, CST-100, Orion) are very close and suitable only for a flight to the moon, which is only 3 days away. True, there is an idea after takeoff to inflate additional rooms. In the fall of 2016, the inflatable module was tested on the ISS and showed itself well. Thus, the technical possibility of a flight to Mars will soon appear. So what's the problem? In a man!
We are constantly exposed to the natural radioactivity of terrestrial 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 the atmosphere of the planet, as well as its body, covering the lower hemisphere. The atmosphere no longer helps in low Earth orbit where the cosmonauts of the ISS are working, therefore the background radiation increases hundreds of times. In open space, it is still several times higher. This significantly limits the duration of the safe human stay in space. It should be noted 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 (acceptable danger level), which limits the duration of their work on the ISS to one year. A flight to Mars with a return to Earth at best (if there are no powerful flares on the Sun) will result in a dose of 80 rem, which will create a greater likelihood of cancer. This is the main obstacle for manned flight to Mars. Is it possible to protect astronauts from radiation? Theoretically, you can.
We are protected on Earth by the atmosphere, the thickness of which by the amount of a substance per square centimeter is equivalent to a 10-meter layer of water. Light atoms better disperse the energy of cosmic particles, therefore 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. Send such a ship to Mars can not afford a modern and even promising rocket.
Oh well. Suppose there are volunteers who are 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 we expect them to do the job? Remember how astronauts, after spending half a year on the ISS, feel immediately after landing on the ground? They are carried on their hands, put on stretchers and for two or three weeks they are rehabilitated, restoring bone strength and muscle strength. And on Mars, no one will stand on their hands. There it will be necessary to independently go out and work in heavy hollow space suits, as on the Moon. After all, the pressure of the atmosphere on Mars is almost zero. The spacesuit is very heavy. On the moon it was relatively easy to move in it, because gravity is there 1/6 of the earth, and for three days of flight to the moon, the muscles do not have time to weaken. The cosmonauts will arrive on Mars after spending many months in conditions of weightlessness and radiation, and the force of gravity on Mars is two and a half times the lunar one. In addition, radiation on the surface of Mars itself is almost the same as in outer space: Mars does not have a magnetic field, and its atmosphere is too rarefied to serve as protection. So the Martian film is fantastic, very beautiful, but unreal.
How did we imagine the Martian base before? We flew, put laboratory modules on the surface, live in them and work. And now, here's how: they flew in, dug in, built shelters at a depth of at least 2-3 meters (this is a fairly reliable protection against radiation) and try less often and not to go to the surface for a long time. Outputs to the surface are episodic. Basically we sit under the ground and manage the work of the rovers. So they and the Earth can be controlled, even more efficiently, cheaper and without risk to health. What has been done for several decades.
That learned about Mars robots -.
Illustrations prepared by V. G. Surdin and N. L. Vasilyeva using NASA photographs and images from public sites
What terrestrial planets do you know? List in your head and see if you think it is right :). Now we will tell you about them.
Planets Mercury, Venus, Earth and Mars so are the four sisters, but there is no complete resemblance between them. Each of them developed in its own way.
The closest to the Sun formed in a very hot area. Under the influence of high temperatures, light gases moved to the periphery of the solar system, so the terrestrial planets consist of such heavy elements as carbon, iron, silicon. That is, they are solid and stony, in contrast to the planets formed far from and consisting mainly of gas. The terrestrial planets have undergone dramatic changes since their inception. Their primary atmosphere disappeared, her deputies light gases, rising from the inner hot zones of the planets. Heavy elements moved inward and formed the core of such a planet, volcanic eruptions changed their relief. The past since 4.5 billion years have changed the face of the planets, almost similar at birth so different today.
MercuryA small planet located close to the sun, with a very rarefied atmosphere, is a desert with craters, burned out by the sun. Unlike other terrestrial planets, Mercury is a planet on which nothing remarkable happens, except perhaps for the constant light meteor shower.
It is likely that we have long Venus there were oceans, well, since this planet is quite close to the Sun, the water evaporated and disappeared into space. Currently, a 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. Hidden under the clouds, the surface of the planet was studied with the help of the interplanetary station Magellan in 1990. Huge plains, mountains, deep rifts, volcanoes and several meteorite craters were discovered.
Most of the surface Of the earth occupied by water, remaining in a liquid state due to this, that the planet is not too close and not too far from the Sun. The atmospheric envelope, a state mainly of nitrogen, oxygen, a small amount of carbon dioxide and water vapor, creates a known climate. Today's volcanic processes are much less significant than in the past.
Have Mars there used to be a different, denser atmosphere conducive to a mild climate; there were reiki and oceans. Well, since the planet is small, and the mass is not sufficient for the force of gravity to hold the gas, most of them disappeared into space. Now the atmosphere is made of carbon dioxide. The temperature has dropped, the water is now in a frozen state under a layer of soil. From within, Mars also cooled off faster than Venus and Earth, and huge volcanoes went out a billion years ago. Sometimes hurricane winds raise clouds of dust, and it takes weeks for them to settle on the surface.
Introduction
Among the numerous celestial bodies studied by modern astronomy, the planets occupy a special place. After all, we all know well that the Earth on which we live is a planet, so the planets are bodies, basically similar to our Earth.
But in the world of planets, we will not meet even two completely alike. The variety of physical conditions on the planets is very large. The distance of the planet from the Sun (and hence the amount of solar heat, and the surface temperature), its dimensions, gravity stress on the surface, the orientation of the axis of rotation, determining the change of seasons, the presence and composition of the atmosphere, the internal structure and many other properties are different for all of nine planets of the solar system.
Speaking about the diversity of conditions on the planets, we can learn more deeply the laws of their development and find out their interrelation between these or other properties of the planets. For example, its ability to hold the atmosphere of a composition depends on the size, mass and temperature of the planet, and the presence of the atmosphere in turn affects the thermal regime of the planet.
As the study shows the conditions under which the birth and further development of living matter is possible, only on the planets can we look for signs of the existence of organic life. That is why the study of the planets, in addition to the 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, and for other areas of science, primarily 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 closest planet to the Sun of the solar system. The average distance from Mercury to the Sun is only 58 million km. Among the major planets, it has the smallest dimensions: its diameter is 4865 km (0.38 of the diameter of the Earth), mass is 3.304 * 10 23 kg (0.055 is the mass of the Earth, or 1: 6025000 is the mass of the Sun); average density of 5.52 g / cm 3. Mercury is a bright star, but to see it in the sky is not so simple. 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 to the left (to the east), then to the right (to the west) only a short distance that does not exceed 28 O. Therefore, it can see only in those days of the year when it departs from the Sun at the greatest distance. Suppose, for example, Mercury moved away from the Sun to the left. The sun and all the stars in their daily movement float through the sky from left to right. Therefore, the sun first sets, and after an hour with a little Mercury sets, it is necessary to search for this planet low above the Western horizon.
Motion.
Mercury moves around the Sun on average at a 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 in aphelion 70 million km. The planet flies around the Sun in three Earth months or in 88 days at a speed of 47.9 km / s. Moving along its path around the Sun, Mercury at the same time turns around its axis so that always one and the same half of it is facing the Sun. This means that on one side of Mercury is always day, and on the other - night. In the 60s. using radar observations, it was found that Mercury rotates around an axis in the forward direction (that is, as in orbital motion) with a period of 58.65 days (relative to the stars). The duration of the solar day on Mercury is 176 days. The equator is inclined to the plane of its orbit by 7 °. The angular velocity of the axial rotation of Mercury is 3/2 of the orbital and corresponds to the angular velocity 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 be deprived of the atmosphere, although polarization and spectral observations indicate the presence of a weak atmosphere. With the help of “Mariner-10”, the presence of a highly discharged gas envelope, consisting mainly of helium, was found in Mercury. This atmosphere is in dynamic equilibrium: each helium atom is in it for about 200 days, after which it leaves the planet, while another particle from the plasma of the solar wind takes its place. In addition to helium, an insignificant amount of hydrogen was found in the atmosphere of Mercury. It is about 50 times smaller than helium.
It also turned out that Mercury has a weak magnetic field, the intensity of which is only 0.7% of the earth. The slope of the dipole axis to the axis of rotation of Mercury is 12 0 (the Earth has 11 0)
The pressure at the surface of the planet is about 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 and warms it 7 times stronger than ours. On the day side of Mercury is terribly hot, there is an eternal hell there. Measurements show that the temperature there rises to 400 o above zero. But on the night side there should always be a strong 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 ice desert, perhaps covered with frozen gases.
Surface.
From the flight path of the Mariner 10 spacecraft in 1974, more than 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 was in darkness from Earth. The abundance of craters is the most obvious feature of its surface, which in its first impression can be likened to the Moon.
Indeed, the morphology of craters is close to lunar, their impact origin is unquestionable: the majority of the shaft has delineated traces of emissions of the material crushed upon impact with the formation of characteristic bright rays and the field of secondary craters in some cases. Many craters have a central hill and a terraced structure on the inner slope. It is interesting that not only practically all large craters with a diameter of more than 40-70 km have such features, but also a much larger number of craters of smaller size, within 5-70 km (of course, we are talking about well-preserved craters). These features can be attributed both to the expense of the greater kinetic energy of bodies that fell to the surface, and to the expense of the surface material itself.
The degree of erosion and smoothing of craters varies. In general, the Mercury craters are less deep compared to the lunar craters, 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 than on the Moon, and deposits of crushed material to a lesser extent mask the primary forms of relief. The secondary craters themselves are deeper than lunar craters, which again is explained by the fact that the fragments falling to the surface experience a greater acceleration of gravity.
Just like on the Moon, depending on the relief, it is possible to distinguish the prevailing uneven “mainland” and much smoother “sea” areas. The latter are mainly hollows, which, however, are significantly smaller than on the moon, their dimensions usually do not exceed 400-600 km. In addition, some basins are poorly distinguishable against the background of the surrounding relief. The exception is the mentioned extensive Canoris Basin (Sea of Heat) about 1300 km long, resembling the famous Sea of Rains on the Moon.
In the predominant continental part of the surface of Mercury, it is possible to distinguish both highly craterized areas, with the greatest degree of crater degradation, and old inter-crater plateaus, which occupy vast territories, indicating a widely developed ancient volcanism. These are the most ancient preserved relief forms of the planet. The flattened 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 strokes resembling the moon. Some of the flat areas adjacent to the basins were probably formed during the deposition of material thrown out of them. At the same time, for most of the plains, quite definite evidence of their volcanic origin has been found, however, this volcanism is later than on the inter-crater plateaus. Careful examination reveals another interesting feature that sheds light on the history of the formation of the planet. We are talking about the characteristic traces of tectonic activity on a global scale in the form of specific steep ledges, or escarpment slopes. Escarpes have a length of 20-500 km and a height of slopes from a few hundred meters to 1-2 km. In their morphology and geometry of location on the surface, they differ from the usual tectonic discontinuities and discharges observed on the Moon and Mars, and were rather formed due to thrusts, stratifications due to the stress in the surface layer that occurred during Mercury compression. This is evidenced by the horizontal displacement of the shafts of some craters.
Some of the escapes were bombarded and partially destroyed. This means that they formed earlier than craters on their surface. By narrowing the erosion of these craters, it can be concluded that crust compression occurred during the formation of “seas” about 4 billion years ago. The most likely cause of compression is probably to be considered the onset of the cooling of Mercury. According to another interesting suggestion put forward by a number of specialists, an alternative mechanism for the powerful tectonic activity of the planet during this period could be tidal slowing down of the planet's rotation by about 175 times: from the originally estimated value of about 8 hours to 58.6 days.
Venus.
General information.
Venus is the second closest to the Sun planet, almost the same size as the Earth, and its mass is more than 80% of the Earth’s mass. For these reasons, Venus is sometimes called the twin or sister of Earth. However, the surface and atmosphere of these two planets are completely different. On Earth, there are rivers, lakes, oceans and the atmosphere we breathe. Venus is a scorchingly 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 the circle than our planet. Venus receives more than two times more light and heat from the Sun than the Earth. Nevertheless, frost prevails from the shadow side on Venus more than 20 degrees below zero, since the sun's rays do not fall here for a very long time. The planet has a very dense, deep and very cloudy atmosphere, which does not allow us to see the surface of the planet. The atmosphere (gas envelope) was discovered by MV Lomonosov in 1761, which also showed the similarity of Venus with the Earth. The planet has no satellites.
Motion.
Venus has an almost circular orbit (eccentricity of 0.007), which it bypasses in 224.7 Earth days at a speed of 35 km / s. at a distance of 108.2 million km from the Sun. Venus makes a turn around the axis in 243 Earth days - the maximum time among all the planets. Around its axis, Venus rotates in the opposite direction, that is, in the direction opposite to the movement in orbit. Such a slow, and, moreover, reverse rotation means that, when viewed from Venus, the Sun rises and sets only twice a year, since Venusian days are 117 Earthly. The axis of rotation of Venus is almost perpendicular to the orbital plane (tilt 3 °), so there are no seasons of the year - 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 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 relatively easily pass through the clouds of its atmosphere and heat the surface of the planet, but the thermal infrared radiation of the surface itself goes 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 the global temperature by 30 ° C, and on Venus, it raises the temperature by another 400 ° C. Studying the physical consequences of the strongest greenhouse effect on Venus, we are well aware of the results that accumulation of excess heat on the Earth can cause, due to the growing concentration of carbon dioxide in the atmosphere due to the burning of fossil fuels - coal and oil.
In 1970, the first spacecraft arriving on Venus was able to withstand the terrible heat for only about one hour, but this was just enough to send data on the surface conditions to Earth.
Atmosphere.
The mysterious atmosphere of Venus has been the centerpiece of the research program with the help of automatic vehicles over the past two decades. The most important aspects of her research were chemical composition, vertical structure and dynamics of the air environment. Much attention was paid to the cloud cover, which plays the role of an insurmountable barrier for the electromagnetic waves of the optical range to penetrate deep into the atmosphere. During the television filming of Venus, it was possible to obtain an image of only the cloud cover. The extraordinary dryness of the air environment and its phenomenal greenhouse effect were incomprehensible, due to which the actual temperature of the surface and lower layers of the troposphere was more than 500 higher than the effective (equilibrium).
The atmosphere of Venus is extremely hot and dry, due to the greenhouse effect. It is a dense blanket of carbon dioxide, keeps the heat from the sun. As a result, a large amount of thermal energy accumulates. The pressure at the surface is 90 bar (as in the Earth seas at a depth of 900 m). Space ships 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 is able to act as a kind of veil, retaining 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 detected 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, while on Venus it is all concentrated in the atmosphere. In the afternoon, the surface of the planet is illuminated by diffused sunlight at about the same intensity as on an overcast day on Earth. At night, Venus has seen a lot of lightning.
The clouds of Venus are composed 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 30 km, the temperature is about 430 K. It is even lower so hot that there are no clouds. Of course, on the surface of Venus there is no liquid water. 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, making a turn 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 in diameter 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 to occur, so there is no significant weathering (weathering) there. So, volcanoes and craters have not changed much since they were formed millions of years ago.
Venus is covered in hard rocks. Red-hot lava circulates beneath them, causing tension in a thin surface layer. Lava is constantly erupting from holes and gaps in hard rock. In addition, volcanoes all the time throw out streams 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 lava bubbles form on the surface of the dome, which then fall.
On the surface of Venus, a rock rich in potassium, uranium and thorium was found, which in terrestrial conditions corresponds to the composition of not primary volcanic rocks, but secondary ones that have undergone exogenous processing. In other places on the surface lies the large-cube and block material of dark rocks with a density of 2.7-2.9 g / cm and other elements characteristic of basalt. Thus, the surface rocks of Venus turned out to be the same as on the Moon, Mercury, and Mars, which were poured out by igneous rocks of basic composition.
Little is known about the internal structure of Venus. It probably has a metal core that occupies 50% of the radius. But the planet does not have a magnetic field due to its very slow rotation.
Venus is by no means a hospitable world, as it was once supposed. 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 to be a more promising object for space exploration than Mars.
Land.
General information.
Earth is the third planet from the Sun of 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 surface area of the Earth is 510.2 million km², of which approximately 70.8% is in the World Ocean. Its average depth is about 3.8 km, the maximum (Mariana Trench in the Pacific Ocean) is 11.022 km; the volume of water is 1,370 million km³, the average salinity is 35 g / l. Land is respectively 29.2% and forms six continents and islands. It rises above sea level by an average of 875 m; the highest altitude (the summit of Chomolungma in the Himalayas) is 8848 m. Mountains occupy over 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and light forests - about 20%, forests - about 30%, glaciers - over 10%. Over 10% of the land is occupied by agricultural land.
The Earth has a single satellite - the Moon.
Due to its unique, perhaps the only natural conditions in the Universe, the Earth became the place where organic life arose and developed. By modern cosmogonical ideas, the planet was formed about 4.6 - 4.7 billion years ago from a protoplanetary cloud captured by the attraction of the Sun. Formation of the first, most ancient of the studied rocks took 100-200 million years. Approximately 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 a modern type of person dates back to the time of the retreat of the first glacier, that is, about 40 thousand years ago.
Motion.
Like other planets, it moves around the Sun in an elliptical orbit, the eccentricity of which is 0.017. The distance from the Earth to the Sun at different points in the orbit varies. The average distance is about 149.6 million km. In the course of the movement of our planet 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 tilted towards the Sun with its northern hemisphere, and in others - the southern. The period of revolution around the Sun is 365.256 days, with a daily rotation of 23 hours and 56 minutes. The axis of rotation of the Earth 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 a long evolution under the influence of geological, chemical and biological processes. Perhaps the primary atmosphere of the earth was rich in hydrogen, which then evaporated. Degassing of the subsoil filled the atmosphere with carbon dioxide and water vapor. But steam condensed in the oceans, and carbon dioxide was bound in carbonate rocks. Thus, nitrogen remained in the atmosphere, and oxygen appeared gradually as a result of the life activity of the biosphere. 600 million years ago, the oxygen content in the air was 100 times lower than the current one.
Our planet is surrounded by a vast atmosphere. In accordance with the temperature, the composition and physical properties of the atmosphere can be divided into different layers. The troposphere is an area lying between the surface of the Earth and a height of 11 km. It is a rather thick and thick 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. In the troposphere there are clouds, precipitation, etc. The layer separating the troposphere from the next atmospheric layer, the stratosphere, is called the tropopause. This is an area of extremely low temperatures.
The composition of the stratosphere is the same as that of the troposphere, but ozone appears and concentrates in it. The ionosphere, that is, the ionized air layer, is formed both in the troposphere and in the lower layers. It reflects high frequency radio waves.
The atmospheric pressure at ocean level is under normal conditions about 0.1 MPa. It is believed that the earth's atmosphere has changed dramatically in the process of evolution: it was enriched with oxygen and acquired a modern composition as a result of long-term interaction with rocks and with the participation of the biosphere, that is, plant and animal organisms. Evidence that such changes really occurred, are, for example, deposits of coal and thick layers of carbonate deposits in sedimentary rocks, they contain a huge amount 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 originated from the gaseous products of volcanic eruptions; Its composition is judged by the chemical analysis of gas samples "immured" in the cavities of ancient rocks. In the studied samples, whose age is approximately 3.5 billion years, approximately 60% of carbon dioxide is contained, and the remaining 40% are sulfur compounds, ammonia, hydrogen chloride and hydrogen fluoride. Nitrogen and inert gases are found in small quantities. All oxygen was chemically bound.
For biological processes on Earth, the ozonosphere is of great importance - an ozone layer located at an altitude of 12 to 50 km. The region above 50-80 km is called the ionosphere. Atoms and molecules in this layer are intensely ionized under the influence of solar radiation, in particular, ultraviolet radiation. If it were not for the ozone layer, the radiation fluxes would reach the Earth's surface, causing destruction in the living organisms existing there. Finally, at distances of more than 1000 km, gas is so rarefied that collisions between molecules cease to play a significant role, and atoms are more than half ionized. At a height of about 1.6 and 3.7 of the Earth's radii, the first and second radiation belts are located.
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 from seismic events during natural earthquakes and as a result of explosions. Based on these studies, the Earth is conditionally divided into three areas: the crust, the mantle and the core (in the center). The outer layer - the core - has an average thickness of about 35 km. The main types of the crust are continental (continental) and oceanic; in the transition zone from the continent to the ocean, the crust of the intermediate type is developed. The thickness of the crust varies within fairly wide limits: the oceanic crust (taking into account the water layer) has a thickness of about 10 km, while the thickness of the continental crust is ten times more. Surface deposits occupy a layer about 2 km thick. Below them is a granite layer (on the continents its thickness is 20 km), and below it is approximately 14 km (both on the continents and in the oceans) basalt layer (lower crust). The density in the center of the Earth is about 12.5 g / cm³. Average densities are: 2.6 g / cm ³ - at the surface of the Earth, 2.67 g / cm ³ - at granite, 2.85 g / cm ³ - at basalt.
The Earth’s mantle, which is also called the silicate shell, extends to a depth of approximately from 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. The densities in the mantle increase as the depth increases from about 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 the continental drift, which significantly affects the appearance of the Earth, but also relate to the location of seismic zones on the planet. Another boundary detected by seismic methods (Gutenberg boundary) - between the mantle and the outer core - lies at a depth of 2,775 km. On it, the speed of longitudinal waves falls from 13.6 km / s (in the mantle) to 8.1 km / s (in the core), and the speed of the 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 above 5,120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth’s mass. Presumably, this is an iron-nickel alloy (80% Fe, 20% Ni).
The gravitational field of the Earth with a high accuracy is described by the law of world wide Newton. The acceleration of free fall over the surface of the Earth is determined by both the gravitational and centrifugal force due to the rotation of the Earth. The acceleration of free fall 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 is made up of constant (or varying rather slowly) and variable parts; the latter is usually referred to as magnetic field variations. The main magnetic field has a structure close to the dipole. The magnetic dipole moment of the Earth, equal to 7.98T10 ^ 25 units of the SGSM, is directed approximately opposite to the mechanical, although at present the magnetic poles are somewhat shifted relative to the geographic poles. Their position, however, changes with time, and although these changes are rather slow, for geological periods, according to paleomagnetic data, even magnetic inversions, that is, polarity inversions, are detected. The magnetic field strengths at the north and south magnetic poles are 0.58 and 0.68 Oe, respectively, and around 0.4 Oe at the geomagnetic equator.
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 a natural satellite of the Earth and the closest celestial body to us. The average distance to the moon - 384,000 kilometers, the diameter of the moon about 3476 km. The average density of the moon is 3,347 g / cm³ or about 0.607 of the average density of the earth. The mass of the satellite is 73 trillion tons. Acceleration of gravity on the surface of the moon 1,623 m / s².
The moon moves around the Earth at an average speed of 1.02 km / s in an approximately elliptical orbit in the same direction as the vast majority of other bodies in the solar system, that is, counterclockwise, when looking at the moon's orbit from the North Pole of the world. The period of the Moon’s orbit around the Earth, the so-called sidereal month, is equal to 27.321661 days, but it is subject to slight fluctuations and a very small secular reduction.
Without being protected by the atmosphere, the surface of the moon heats up to + 110 ° C in the daytime and cools down to -120 ° C at night, however, as radio observations have shown, these huge temperature fluctuations penetrate only a few decimeters due to the extremely low thermal conductivity of the surface layers.
The relief of the lunar surface was mainly clarified as a result of many years of telescopic observations. "Moonsea", occupying about 40% of the visible surface of the moon, are flat lowlands, crossed by cracks and low winding trees; There are relatively few large craters on the seas. Many seas are surrounded by concentric ring ridges. The rest of the 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 the 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. Equatorial radius is equal to 3380 km. The average density of the planet is 3950 kg / m³. Mars has two moons - Phobos and Deimos.
Atmosphere.
The planet is shrouded in a gas envelope - an atmosphere that is less dense than the earth. Even in the deep depressions of Mars, where the pressure of the atmosphere is greatest, it is about 100 times less than at the surface of the Earth, and at the level of the Martian mountain peaks - 500-1000 times less. In composition, it resembles the atmosphere of Venus and contains 95.3% carbon dioxide mixed with 2.7% nitrogen, 1.6% argon, 0.07% carbon monoxide, 0.13% oxygen and about 0.03% water vapor, the content which changes, as well as impurities of neon, krypton, xenon.
The average temperature on Mars is much lower than on Earth at around -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 the frost can reach -125 ° C. Such sudden temperature drops are caused by the fact that the rarefied atmosphere of Mars is not capable of holding heat for a long time.
Above the surface of the planet often strong winds blow, the speed of which reaches 100 m / s. Low gravity allows even rarefied streams of air to lift huge clouds of dust. Sometimes quite large areas on Mars are covered by a grand dust storm. The global dust storm raged from September 1971 to January 1972, raising about a billion tons of dust to the atmosphere to a height of more than 10 km.
Water vapor in the atmosphere of Mars is quite a bit, but at low pressure and temperature, it is in a state close to saturation, and often gathers into clouds. Martian clouds are rather inexpressive in comparison with terrestrial ones, although they have various shapes and types: cirrus, undulating, leeward (near large mountains and under the slopes of large craters, in places protected from the wind). Over lowlands, canyons, valleys - and at the bottom of craters in the cold hours of the day there are often fogs.
As the pictures from the American landing stations Viking-1 and Viking-2 showed, the Martian sky has a pinkish color in clear weather, which is explained by the scattering of sunlight on specks and the backlighting of the smoke on the orange surface of the planet. In the absence of clouds, the gas envelope of Mars is much more transparent than the earth's, including for ultraviolet rays that are dangerous to living organisms.
Seasons.
Sunny day on Mars lasts 24 hours 39 minutes. 35 s A significant inclination of the equator to the orbital plane leads to the fact that in some parts of the orbit, the northern latitudes of Mars are illuminated and heated by the Sun, in others - the southern ones, that is, the seasons change. The Martian year lasts about 686.9 days. The change of seasons on Mars is the same as on Earth. Seasonal changes are most pronounced in the polar regions. In winter, the polar caps occupy a large area. The boundary of the north polar cap can move away from the pole at a third of the distance from the equator, and the boundary of the south cap overcomes half of this distance. Such a difference is caused by the fact that in the northern hemisphere, winter begins when Mars passes through the perihelion of its orbit, and in the southern hemisphere when it passes through aphelion. Because of this, winter is colder in the southern hemisphere than in the northern. The ellipticity of the Martian orbit leads to significant differences in the climate of the northern and southern hemispheres: in mid-latitudes, winter is colder and summer is warmer than in southern, but shorter than in northern .. When summer begins in the northern hemisphere of Mars, the polar polar cap decreases rapidly, but at this time another grows - near the south pole where winter comes. At the end of the 19th – beginning of the 20th century, the polar caps of Mars were believed to be glaciers and snow. According to modern data, both polar caps of the planet - northern and southern - are composed of solid carbon dioxide, i.e., dry ice, which forms when carbon dioxide freezes, which is part of the Martian atmosphere, and water ice mixed with mineral dust.
The structure of the planet.
Due to the low mass, 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 density distribution in the planet. The core may have a radius of up to half the radius of the planet. Apparently, it consists of pure iron or from an alloy of Fe-FeS (iron-iron sulfide) and, possibly, hydrogen dissolved in them. Apparently, the core of Mars is partially or completely in the liquid state.
Mars should have a powerful crust 70-100 km thick. Between the core and the crust is a silicate mantle enriched in iron. The red iron oxides present in the surface rocks determine the color of the planet. Now Mars continues to cool.
The seismic activity of the planet is weak.
Surface.
The surface of Mars, at first glance, resembles the moon. However, in fact, its relief is very diverse. Throughout the long geological history of Mars, volcanic eruptions and marshokes have changed its surface. Deep scars on the face of the god of war left meteorites, wind, water and ice.
The surface of the planet consists of two contrasting parts: the ancient highlands, covering the southern hemisphere, and the younger plains, concentrated in northern latitudes. In addition, there are two large volcanic areas - Elysium and Farsida. The difference in altitude between mountain and plain areas reaches 6 km. Why different areas are so different from each other is still unclear. Perhaps this division is associated with a very long-term catastrophe - the fall of a large asteroid on Mars.
The high-altitude part retained traces of active meteorite bombardment, which took place about 4 billion years ago. Meteorite craters cover 2/3 of the planet’s surface. In the old highlands there are almost as many of them as on the moon. But many Martian craters, due to weathering, managed to “lose their shape”. Some of them, apparently, were once washed away by streams of water. The northern plains look completely different. 4 billion years ago there were a lot of meteor craters on them, but then the catastrophic event, which was already mentioned, erased them from 1/3 of the surface of the planet and its relief in this area began to form anew. Some meteorites fell there and later, but in general there are few impact craters in the north.
The appearance of this hemisphere is determined by volcanic activity. Some of the plains are completely covered with ancient igneous rocks. Flows of liquid lava spread over the surface, froze, new streams flowed along them. These petrified "rivers" are concentrated around large volcanoes. At the end of lava languages, structures similar to terrestrial sedimentary rocks are observed. Probably, when the red-hot igneous masses melted layers of underground ice, rather extensive reservoirs formed on the surface of Mars, which gradually dried out. The interaction of lava and underground ice also led to the appearance of numerous furrows and cracks. Far from the volcanoes in the lowlands of the northern hemisphere, sand dunes stretch. Especially a lot of them at the north polar cap.
The abundance of volcanic landscapes suggests that in the distant past, Mars experienced a rather turbulent geological epoch, most likely it ended about a billion years ago. The most active processes occurred in the areas of Elysium and Farsida. At one time, they were literally squeezed out of the depths of Mars and now rise above its surface in the form of tremendous swellings: Elysium 5 km high, Farsid - 10 km. Numerous faults, cracks, ridges are concentrated around these blisters - traces of long-standing processes in the Martian crust. The most grandiose system of canyons several kilometers deep - the valley of Mariner - begins at the top of the Farsis 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 the atmosphere of Mars was denser, water could flow into the canyons, creating deep lakes in them.
The volcanoes of Mars are exceptional by earthly standards. But even among them, the Olympus Volcano stands out, located in the north-west of the Farsida Mountains. The diameter of the base of this mountain reaches 550 km, and its height is 27 km, i.e. it is three times the summit of Everest, the highest peak of the Earth. Olympus is crowned with a huge 60-km crater. To the east of the highest part of the mountains Farsida discovered another volcano - Alba. Although he can not compete with Olympus in height, the diameter of its base is almost three times larger.
These volcanic cones resulted from the calm outpourings of very liquid lava, similar in composition to the lava of terrestrial volcanoes of the Hawaiian Islands. Traces of volcanic ash on the slopes of other mountains suggest that sometimes catastrophic eruptions occurred on Mars.
In the past, running water played a huge role in the formation of the Martian relief. In the early stages of the study, Mars was presented to astronomers as a desert and anhydrous planet, but when Mars was able to photograph the surface from close range, it turned out that in the old highlands often there are seemingly abandoned scour water. Some of them look as if many years ago they were pierced by stormy, impetuous streams. Sometimes they stretch for many hundreds of kilometers. Some of these "streams" have a rather respectful age. Other valleys are very similar to the channels of calm earthly rivers. Their appearance is likely to be due 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 of the American astronomer Asaf Hall. Such satellites received names from Greek mythology: Phobos and Deimos - the sons of Ares (Mars) and Aphrodite (Venus), always accompanied their father. Translated from the Greek, “phobos” means “fear”, and “deimos” means “horror”.
Phobos. Deimos.
Both satellites of Mars are moving almost exactly in the equatorial plane of the planet. Using spacecraft, it was established that Phobos and Deimos are irregularly shaped and, in their orbital position, remain always turned to the planet by the same side. The size of Phobos is about 27 km, and Deimos - about 15 km. The surface of the moons of Mars consists of very dark minerals and is covered with numerous craters. One of them - Phobos has a diameter of about 5.3 km. Craters are probably born of meteorite bombardment, the origin of the system of parallel furrows is unknown. The angular velocity of the orbital motion of Phobos is so great that it, overtaking the axial rotation of the planet, rises, unlike other luminaries, in the west, and sets in the east.
The search for life on Mars.
For a long time Mars has been searching for forms of extraterrestrial life. In the study of the planet by the spacecraft of the Viking series, 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 the determination of photosynthesis with carbon, the label decomposition experiment was based on the assumption of the need for water to exist, and the gas exchange experiment took into account that Martian life should use water as a solvent. Although all three biological experiments gave a positive result, they are likely to have a non-biological 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 of the entire planetary system, if nothing unexpected happens, seems clear. The probability that the established order of motion of the planets will be disturbed by some wandering star is small, even for several billion years. In the near future, one does not have to expect strong changes in the energy flow of the Sun. Probably, glacial periods may repeat. A person is able to change the climate, but it may make a mistake. Continents in subsequent periods will rise and fall, but we hope that the processes will be slow. Massive meteorites may fall from time to time.
But basically the solar system will retain its modern look.
Plan.
1. Introduction.
2. Mercury.
3. Venus.
6. Conclusion.
7. Literature.
Planet Mercury.
The surface of Mercury.
Planet Venus.
The surface of Venus.
Planet Earth.
Land surface.
The planet Mars.
Surface of mars.
Interesting facts about the terrestrial planets brief records
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