Physical conditions on the moon. Planet satellites.
moon is the only natural satellite of the Earth. This is a spherical body with a radius of 1738 km. The mass of the Moon is only 81 times less than the mass of the Earth. The average density of the Moon is 0.6 of the density of the Earth, and the acceleration of free fall is 6 times less than the Earth's, that is, objects on the lunar surface weigh 6 times less than on Earth. A solar day on the Moon lasts a synodic month (29.5 Earth days). There is no liquid water on the Moon and there is practically no atmosphere. During the lunar day, which lasts about 15 Earth days, the surface has time to heat up to +130 °C, and at night it cools down to -170 °C.
With the naked eye, light and dark areas are distinguishable on the lunar surface. Dark, relatively flat areas of the surface, called "seas", occupy 17% of the entire surface of the moon. The lighter mountainous areas are the "continents". They occupy the rest of the surface and are characterized by the presence of mountain ranges, ring mountains, craters.
The names of the mountain ranges, which usually stretch along the outskirts of the seas, are borrowed from the terrestrial ones - the Apennines, the Caucasus, the Carpathians, etc. The Apennines have a maximum height of about 6 km, and the Carpathians are only 2 km.
The most numerous formations on the lunar surface are craters from microscopic sizes to more than 100 km in diameter. The crater consists of an annular swell and an inner plain. Most of the "young" craters have central hills at the bottom. The impact of a large meteorite or a small asteroid on the surface of the Moon is accompanied by an explosion. During the explosion, the lunar substance is ejected, and a crater is formed on the surface.
Space exploration has significantly developed our knowledge of the Moon. In 1959, the far side of the Moon was photographed for the first time by the Soviet apparatus Luna-3. In 1965, the first complete map of the Moon appeared, compiled under the scientific guidance of Yu. N. Lipsky, after whom the crater on the Moon is named.
US astronauts Neil Armstrong and Edwin Aldrin on July 20, 1969 became the first people to walk on the moon.
The surface layer of a natural satellite of the Earth with a thickness of about 10 m consists of regolith - fine-grained material. The regolith has a low density (upper layer 1200 kg/m 3 ) and very low thermal conductivity (20 times less than air), so even at a depth of about a meter temperature fluctuations are almost imperceptible.
The chemical composition of lunar rocks is very close to that of terrestrial rocks such as basalts.
Space stations have recently discovered reserves of water ice in the polar regions of the moon.
There are several hypotheses for the formation of the moon. According to one of them, the following mechanism of the formation of the Moon is considered. The Earth, having passed the main stages of matter differentiation, collided with a large celestial body (the size of Mars). Oblique impact destroyed only the upper layers of the earth's interior. The substance of the earth's crust and mantle was thrown into the near-Earth orbit, from which the Earth's satellite was formed by merging.
In the solar system at the beginning of the XXI century. 102 natural satellites of the planets are known. Seven satellites, including our Moon, have a diameter greater than that of the planet Pluto, and Ganymede and Titan are even larger than Mercury. Nine more satellites have crossed the thousand-kilometer boundary, the rest are less than 500 km in size.
Small satellites (tens of kilometers in size) are irregularly shaped stone or ice bodies. Their surfaces are dotted with craters, covered with regolith and fine dust.
Satellites of medium size (a few hundred kilometers) are mostly spherical and have a low density. In appearance, they resemble the lunar surface.
The seven largest moons are very diverse. In their structure, they are more similar to the planets of the terrestrial group. They have a complex internal structure. They have an atmosphere, a magnetic field. Io, a moon of Jupiter, has a 30 km thick silicate (stony) crust, under it at a depth of 100 km is a liquid ocean of magma with a temperature of up to 2000 K, which feeds numerous volcanoes. The remaining satellites are covered with an ice shell of various thicknesses, under which there is a rocky mantle. At Triton (a moon of Neptune), an ice shell 180 km thick lies on a water ocean with impurities of ammonia and methane. The depth of the ocean is 150 km. According to many indications, there is also a layer of liquid water or ice with water under the icy crust of Europa (a satellite of Jupiter).
On the surface of Triton and Ganymede (satellite of Jupiter), traces of tectonic activity are visible: faults, compression, cracks, small ridges. Callisto (a moon of Jupiter) differs from them in the presence of numerous impact craters.
The ice shell of Europa is intersected by a network of light and dark narrow stripes. These are cracks in the thick ice crust caused by Jupiter's tidal forces.
Titan (saturn's moon) has the most powerful atmosphere. The pressure at the surface is 1.5 times higher than the earth's.
Of the terrestrial planets, apart from the Earth, only Mars has two satellites, discovered in 1877 by the American astronomer Asaph Hall. These are small irregularly shaped stony bodies measuring 27x19 km (Phobos) and 16x11 km (Deimos).
The Moon is the closest terrestrial body to the Earth, as well as its only natural satellite. The Moon is the brightest object in the solar system after the Sun. The Moon is the fifth largest natural satellite in the solar system.
Despite the fact that the Moon is a satellite of the Earth, its parameters and parameters of the environment are very different from those of the Earth.
Table 2 - Basic parameters of the Earth and the Moon.
Deep vacuum, prolonged exposure to active cosmic radiation and solar radiation, the continuous fall of meteorites and low gravity create conditions for the formation of the lunar surface that are unusual for the Earth.
Physical conditions on the surface of the moon
Speaking about the structure of the Moon, we can compare it with the Earth. The moon is made up of a crust, upper mantle, middle mantle, lower mantle, and core.
The atmosphere of the Moon is extremely rarefied. When the surface is not illuminated by the Sun, the content of gases above it does not exceed 2.0 105 particles/cm³, and after sunrise it increases by two orders of magnitude due to degassing of the soil. The rarefied atmosphere leads to a high temperature difference on the surface of the Moon (from? 160 ° C to +120 ° C), depending on the illumination. The temperature of the rocks lying at a depth of 1 m is constant and equal to ?35 °C. Due to the virtual absence of an atmosphere, the sky on the Moon is always black with stars, even when the Sun is above the horizon.
§ 7. Earth and Moon
5. Physical conditions on the moon
Despite the fact that the Moon is located almost at the same distance from the Sun as the Earth, and a unit of its surface receives the same amount of energy as a unit of the Earth's surface, the physical conditions on these cosmic bodies differ significantly. The main reason for such differences is due to the fact that the force of gravity on the Moon is 6 times less than the earth's, so it cannot keep individual gas molecules near the surface. For billions of years, the weather on the Moon is the same: the Sun shines for 2 weeks and the surface heats up to a temperature of +130 °C, and then after a two-week night the surface cools and the temperature drops to -160 °C at dawn. Due to the high daytime temperature, gas molecules leave the sphere of attraction of the Moon, so the existence of a thick atmosphere is impossible there.
On the Moon, even during the day, the sky is dark, as in interplanetary space, there are neither winds nor rains. The change of seasons does not occur because the moon's axis of rotation is almost perpendicular to the plane of the orbit.On the surface of the moon, even unrecoverable
Month
Radius 0.25 R
Weight 1/81 M
Density 3.3 g/cm3
Free fall acceleration 1/6 g
Semi-major axis of the orbit 3.8-10" km
Rotation periods: sidereal 27.3 out. days
synodic 29.5 out. days
Solar day 29.5 out. days
Temperature, ° С: daytime +130
At night -160
For the curious
Of all the astronomical phenomena, perhaps the greatest attention of people is attracted by the eclipse of the Sun, which occurs at the moment when the shadow from the Moon reaches the surface of the Earth. Although the Moon is between the Sun and the Earth every 29.5 days (the phase is the new moon), eclipses occur much less frequently, because the plane of the Moon's orbit is inclined to the ecliptic at an angle of 5 °. There are two points on the orbit at which the Moon crosses the plane of the ecliptic - they are called the nodes of the lunar orbit. An eclipse of the Moon or the Sun can only take place when the Moon is near the node of the orbit. The nodes of the lunar orbit shift in outer space, so eclipses occur at different times of the year. The period of repetition of eclipses, or saros, was known by the Egyptian priests 4000 years ago. Modern calculations give the following value of saros: Gsar = 6585.33 days = 18 years 11 days 8 hours. During one saros, 43 eclipses of the Sun and 25-29 eclipses of the Moon occur in different places on the Earth's surface, and solar and lunar eclipses always occur in pairs with an interval of 2 weeks: if an eclipse of the Sun occurs in one node of the lunar orbit, then after 2 weeks in another node is an eclipse of the moon.
There is not a drop of moisture in the seas, because in a vacuum, water instantly boils and evaporates or freezes. Water in a solid state could be preserved under the surface at a depth of several tens of meters, where the temperature does not change during the day and is equal to -30 °C.
During observations with a telescope, it can be seen that craters predominate on bright continents - round mountains with a diameter of up to several hundred kilometers, which have shafts several kilometers high (Fig. 7.9). Most of the craters are meteoritic in origin, although some of them may have been formed by volcanic eruptions, from which molten lava flowed and filled the lower areas - this is how the seas arose. Volcanic eruptions stopped a long time ago, because the age of the oldest solid rocks on the continents is 4.4 billion years, while the lava in the seas solidified about 3 billion years ago.
For the curious
The fall of meteorites is the main factor that changes the appearance of the surface of the moon and leads to a kind of erosion of the lunar soil. For example, a meteorite with a mass of 1 kg, flying at a speed of 10 km / s, has such a kinetic energy that when it collides with the surfaceThe moon can form a crater with a diameter of 1 m and scatter pebbles and dust over several tens of meters. Thousands of meteorites of various masses are constantly falling on the Moon (see § 11), which continuously change the appearance of its surface. True, large craters with a diameter of several hundred kilometers formed a very long time ago, 4 billion years ago, when more meteorites fell. Over the course of billions of years, cosmic "bombardments" so crushed the top layer of the lunar soil that it turned into "dust".
Rice. 7.8. The seas on the Moon were formed after volcanic eruptions. They have a darker color because there is more iron in the chemical composition, and there is more aluminum in the lighter areas.
Rice. 7.9. Craters on the Moon are now formed after the fall of meteorites, although volcanoes were active 3 billion years ago
The main stages of space exploration of the moon
Year |
Apparatus |
The country |
1959 |
Luna-2 |
the USSR |
1959 |
Luna-3 |
the USSR |
1966 |
Luna-9 |
the USSR |
1969 |
Apollo 11 |
USA |
1970 |
Lunokhod-1 |
the USSR |
The Moon is the closest celestial body to the Earth and therefore the best studied. The closest planets to us are about 100 times further away than the Moon. The Moon is four times smaller than the Earth in diameter and 81 times in mass. Its average density, i.e., less than that of the Earth. Probably, the Moon does not have such a dense core as the Earth has.
We always see only one hemisphere of the Moon, on which neither clouds nor the slightest haze are ever noticeable, which served as one of the proofs of the absence of water vapor and atmosphere on the Moon. This was later confirmed by direct measurements on the lunar surface. The sky on the Moon, even during the day, would be black, as in a vacuum, but the rarefied dust shell surrounding the Moon scatters the sunlight a little.
There is no atmosphere on the Moon that softens the scorching sun rays, does not let X-ray and corpuscular radiation of the Sun dangerous for living organisms to the surface, reduces the return of energy at night to the world space and protects from cosmic rays and micrometeor streams. There are no clouds, no water, no fogs, no rainbows, no dawn with dawn. Shadows are sharp and black.
With the help of automatic stations, it has been established that the continuous impacts of small meteorites, crushing the surface of the Moon, seem to grind it and smooth out the relief. Small fragments do not turn into dust, but under vacuum conditions they quickly sinter into a porous slag-like layer. There is a molecular adhesion of dust in the likeness of pumice. This structure of the lunar crust gives it low thermal conductivity. As a result, with strong temperature fluctuations outside in the bowels of the Moon, even at a shallow depth, the temperature remains constant. The huge temperature differences on the lunar surface from day to night are explained not only by the absence of an atmosphere, but also by the duration of the lunar day and lunar night, which corresponds to our two weeks. The temperature at the subsolar point of the Moon is +120 °C, and at the opposite point of the night hemisphere - 170 °C. This is how the temperature changes during one lunar day!
2. The relief of the moon.
Already since the time of Galileo, maps of the visible hemisphere of the moon began to be compiled. Dark spots on the surface of the Moon were called "seas" (Fig. 47). These are lowlands in which there is not a drop of water. Their bottom is dark and relatively flat. Most of the Moon's surface is occupied by mountainous, lighter spaces. There are several mountain ranges, named, like the terrestrial ones, the Alps, the Caucasus, etc. The height of the mountains reaches 9 km. But the main form of relief are craters. Their annular shafts up to several kilometers high surround large round depressions up to 200 km in diameter, such as Clavius and Shikkard. All major craters are named after scientists. So, on the Moon there are craters Tycho, Copernicus, etc.
Rice. 47. Schematic map of the largest details on the hemisphere of the Moon facing the Earth.
On a full moon in the southern hemisphere, the Tycho crater, 60 km in diameter, is clearly visible through strong binoculars in the form of a bright ring and radially bright rays diverging from it. Their length is comparable to the radius of the moon, and they stretch, crossing many other craters and dark depressions. It turned out that the rays are formed by a cluster of many small craters with light walls.
The lunar relief is best studied when the corresponding area lies near the terminator, i.e., the boundaries of day and night on the Moon. Then, illuminated by the Sun from the side, the slightest irregularities cast long shadows and are easily noticeable. It is very interesting to follow through a telescope for an hour how bright points light up near the terminator on the night side - these are the tops of the shafts of lunar craters. Gradually, a bright horseshoe emerges from the darkness - part of the crater shaft, but the bottom of the crater is still immersed in
Rice. 48. Schematic map of the far side of the Moon, invisible from Earth.
complete darkness. The rays of the Sun, gliding lower and lower, gradually outline the entire crater. It is clearly seen that the smaller the craters, the more of them. They are often arranged in chains and even "sit" on top of each other. The later craters were formed on the shafts of the older ones. In the center of the crater, a hill is often visible (Fig. 49), in reality it is a group of mountains. The crater walls break off in terraces steeply inwards. The bottom of the craters lies below the surrounding area. Consider carefully the view of the inside of the shaft and the central hill of the Copernicus crater, photographed by the artificial satellite of the Moon from the side (Fig. 50). From Earth, this crater is visible directly from above and without such details. In general, craters up to 1 km in diameter are barely visible from the Earth under the best conditions. The entire surface of the moon is pitted with small craters - gentle depressions - this is the result of impacts of small meteorites.
Only one hemisphere of the Moon is visible from Earth. In 1959, the Soviet space station, flying past the Moon, photographed the hemisphere of the Moon invisible from the Earth for the first time. Fundamentally, it does not differ from the visible one, but it has fewer “marine” depressions (Fig. 48). Now detailed maps of this hemisphere have been compiled on the basis of numerous photographs of the Moon taken at close range by automatic stations sent to the Moon. Artificially created devices repeatedly descended to its surface. In 1969, a spacecraft with two American astronauts landed on the surface of the Moon for the first time. To date, several expeditions of US astronauts have visited the Moon and returned safely to Earth. They walked and even drove a special all-terrain vehicle on the surface of the Moon, installed and left various devices on it, in particular seismographs for recording "moonquakes", and brought samples of lunar soil. The samples turned out to be very similar to terrestrial rocks, but they also showed a number of features that are characteristic only of lunar minerals. Soviet scientists received samples of lunar rocks from different places with the help of automatic machines, which, on command from the Earth, took a soil sample and returned with it to Earth. Moreover, Soviet lunar rovers (automatic self-propelled laboratories, Fig. 51) were sent to the Moon, which performed many scientific measurements and analyzes of the soil and significant distances that have passed along the Moon - several tens of kilometers. Even in those parts of the lunar surface that look flat from the Earth, the ground abounds with funnels and is strewn with stones of all possible sizes. The “step by step” lunar rover, controlled from the Earth by radio, moved taking into account the nature of the terrain, the view of which was transmitted
Circus Alphonse, where the release of volcanic gases was observed (the picture was taken by an automatic station near the moon).
(click to view scan)
to earth on television. This greatest achievement of Soviet science and mankind is important not only as a proof of the unlimited possibilities of the human mind and technology, but also as a direct study of the physical conditions on another celestial body. It is also important because it confirms most of the conclusions that astronomers made only from the analysis of the light of the moon, which comes to us from a distance of 380,000 km.
The study of the lunar relief and its origin is also interesting for geology - the Moon is like a museum of the ancient history of its crust, since water and wind do not destroy it. But the Moon is not exactly a dead world. In 1958, the Soviet astronomer N. A. Kozyrev noticed the release of gases from the lunar interior in the Alfons crater.
Apparently, both internal and external forces took part in the formation of the Moon's relief. The role of tectonic and volcanic phenomena is undeniable, since there are fault lines on the Moon, chains of craters, a huge table mountain with slopes the same as those of craters. There is a similarity between lunar craters and the lava lakes of the Hawaiian Islands. Smaller craters were formed from impacts of large meteorites. On Earth, there are also a number of craters formed by the fall of meteorites. As for the lunar "seas", they are apparently formed by melting of the lunar crust and outpourings of lava from volcanoes. Of course, on the Moon, as well as on Earth, the main stages of mountain building took place in the distant past.
Numerous craters found on some other bodies of the planetary system, such as Mars and Mercury, must have the same origin as the lunar ones. Intensive cratering is apparently related to the low gravity on the surface of the planets and to the rarefaction of their atmosphere, which does little to mitigate the bombardment by meteorites.
Soviet space stations established the absence of a magnetic field and radiation belts on the Moon and the presence of radioactive elements on it.
The Moon is the only natural satellite of the Earth. This is a spherical body with a diameter of 3475 km. The mass of the Moon is only 81 times less than the mass of the Earth. The average density of the Moon is 0.6 of the density of the Earth, and the acceleration of free fall is 6 times less than the earth's, i.e., objects on the lunar surface weigh 6 times less than on Earth. A solar day on the Moon lasts a synodic month (29.5 Earth days). There is no liquid water on the Moon and practically no atmosphere. During the lunar day, which lasts about 15 Earth days, the surface has time to heat up to +130 ° C, and at night it cools down to -170 ° C. At high temperatures, the speed of gas molecules exceeds the second cosmic velocity for the surface of the Moon, which is 2.38 km/s, so gases released from the bowels of the Earth's satellite or formed during the fall of meteoroids quickly leave the Moon. Without a gaseous atmosphere, the Moon is exposed to all types of electromagnetic radiation from the Sun, as well as impacts from meteoroids of various sizes.
With the naked eye, light and dark areas are distinguishable on the lunar surface. Dark, relatively flat areas of the surface, called "seas", account for 16.9% of the total surface of the moon. Lighter mountainous areas, the so-called "continents", occupy the remaining surface and are characterized by the presence of mountain ranges, ring mountains, craters. The first detailed lunar map was compiled in 1647 by the Polish astronomer Jan Hevelius. From that time to the present day, the names of the seas have been preserved - the Sea of Tranquility, the Sea of \u200b\u200bCrisis, etc. The names of the mountain ranges, which usually stretch along the outskirts of the seas, are consonant with the earthly ones - the Apennines, the Caucasus, the Carpathians, etc. The Apennines have a maximum height of about 6 km, and the Carpathians - only 2 km.
The most numerous formations on the lunar surface are craters. Their sizes range from microscopic to over 100 km in diameter. The crater consists of an annular swell and an inner plain. Most of the "young" craters have central hills at the bottom. On a full moon near the "young" craters, which are of meteorite origin, one can see ray systems - light bands extending radially from the crater and stretching for hundreds of kilometers.
The impact of a large meteorite or a small asteroid on the surface of the Moon is accompanied by an explosion. In this case, the lunar substance is ejected at different angles. A significant part of it enters space, but some falls back to its surface. Beam systems are formed from jets of crushed matter. To the observer, the rays appear brighter because they reflect light better than dense matter of the same composition.
Large and medium-sized craters are named after prominent scientists: Ptolemy, Archimedes, Plato, Copernicus, Tikhov, Schmidt and others.
Space exploration has significantly deepened our knowledge of the Moon. In 1959, the Soviet apparatus Luna-3 photographed the far, invisible side of the Moon for the first time. In 1965, the first complete map of the Moon appeared, compiled under the scientific guidance of Yu.N. Lipsky.
American astronauts Neil Armstrong and Edwin Aldrin became the first people to walk on the surface of the Moon on July 20, 1969. Astronauts, while on the Moon, could see our Earth in the sky. Over the next three years, American spacecraft of the Apollo series delivered expeditions to different places on the Moon six times (12 astronauts were engaged in research at the landing sites, they managed to collect more than 360 kg of lunar samples). Lunar rocks were also delivered by the Soviet automatic station Luna.
The surface layer of a natural satellite of the Earth consists of fine-grained material - regolith and has a thickness of about 10 m. The composition of the lunar regolith also includes glass spherical microparticles. The fragmentation of lunar rocks occurs mainly due to micrometeorite bombardment and sudden changes in temperature. The regolith has a low density (upper layer 1200 kg/m 3 ) and very low thermal conductivity (20 times less than air), therefore, even at a depth of about 1 m, temperature fluctuations are practically not noticeable.
According to the chemical composition, lunar rocks are very close to basaltic rocks of the Earth. The rocks of the lunar seas are distinguished by a high content of iron and titanium oxides, while the continental rocks are characterized by a high content of aluminum oxides.
Recently, space stations have discovered reserves of water ice in the polar regions of the moon. Since the angle of inclination of the lunar equator to the ecliptic is only 1.5°, the bottom of even shallow craters in the polar regions is never illuminated by the sun's rays. At a constant temperature of -200 °C, the bottom of the polar craters is covered with a mixture of regolith and ice. The source of the origin and accumulation of lunar polar ice can be comets that have fallen into these regions, which are ice bodies.
The internal structure of the Moon has been studied from records of tremors from meteorite impacts, which were recorded by seismographs delivered to the Moon. Under the layer of regolith there is a crust, the thickness of which on the visible (facing the Earth) side is 60 km, and on the reverse side - 100 km. Beneath the crust is the mantle, which is about 1000 km thick. The zone deeper than 1600 km resembles the Earth's mantle, has a thickness of 430 km and a temperature of about 1800 K. Recent studies have confirmed that in the center of the Moon there is a metallic core with a radius of about 300 km, the mass of which is about 3% of the total mass of the Moon.
There are several hypotheses for the formation of the moon. According to one of the most popular, the Moon was formed together with the Earth from one planetesimal. There has been speculation that the Earth may have split in two and that the Pacific Ocean trough is the "pit" left after the Moon "erupted" from the Earth.
Some scientists believe that the Moon was formed by the coalescence of tiny pebbles that orbited the Earth 4.5 billion years ago. The accumulation of particles under the influence of gravitational forces acting near the Earth became a "reduced" version of the same process that took place in the primary solar nebula and led to the birth of planets.
Such a mechanism for the formation of the Moon is also considered. The Earth, having passed the main stages of matter differentiation, collided with a large celestial body (the size of Mars). Oblique impact destroyed only the upper layers of the earth's interior. The substance of the earth's crust and mantle was thrown into the near-Earth orbit, from which the Earth's satellite was formed by merging.
See the table for the parameters of the moon.
