The moon can "launch" the most powerful earthquakes in the world. Gravitational field of the Earth Gravitational field of the moon
This map shows the Moon's gravitational field as measured by NASA's GRAIL mission. Credit: NASA/ARC/MIT.
The first scientific results from the twin GRAIL lunar orbiters provide incredible details of the Moon's interior and the highest-resolution map of the gravitational field of any astronomical body, including Earth.
The Gravity Recovery and Interior Laboratory (GRAIL) data reveals ancient internal structures that were previously unknown, provides details that are five orders of magnitude better than previous studies, and delivers unprecedented information about the Moon's surface and gravitational field.
Instruments on the GRAIL spacecraft can probe inside the planet. The incredible videos reveal a wealth of details that the team said they are just beginning to explore.
Subtracting gravity from surface features provides what is called a Bouguer gravity map. What remains is a type of mass anomaly within the Moon due to either changes in crustal thickness or mantle density. In the video above, the prominent circular areas (in red) indicate well-known mass concentrations or "mascons," but many similar newly discovered features on the far side of the Moon are also visible.
"98% of local gravity is due to topography, while 2% is due to other gravitational features," Zuber said. "You may see the bull's-eye of the lunar mascons, but otherwise you will see a smooth inner surface. This can only happen if early Moon impacts have eroded the inner surface."
These maps of the Moon show Bouguer gravitational anomalies measured by NASA's GRAIL mission. Credit: NASA/JPL-Caltech/CSM.
The Bouguer gravity map also showed evidence of ancient volcanic activity beneath the Moon's surface and strange linear gravity anomalies.
"The gradients of the Bouguer gravity map show features that we did not expect," said Jeff Andrews-Hanna, co-investigator at GRAIL. "We have identified a large population of linear gravity anomalies. We do not see any expression of them on topographic maps, so we conclude that these are ancient internal structures."
A linear gravitational anomaly crossing the Crisium basin on the left side of the Moon was revealed by NASA's GRAIL mission. GRAIL gravity gradient data is shown on the left, with the location of the indicated anomaly. Red and blue correspond to stronger gravity gradients. Topography data over the same region from the Lunar Reconnaissance Orbiter's Lunar Orbiter Laser Altimeter is shown at right; these data show no signs of a gravitational anomaly. Credit: NASA/JPL-Caltech/CSM.
For example, this photograph of the Crisium Basin, which forms one of the eyes of the "man on the moon", gravity maps show a linear feature across the basin, while topographic maps show no such correlating features. "This tells us a gravitational anomaly formed before the impacts," Andrews-Hanna said.
These maps of the near and far side of the Moon show gravitational gradients measured by NASA's GRAIL mission, highlighting a population of linear gravitational anomalies. Credit: NASA/JPL-Caltech/CSM.
Additional evidence shows that the Moon's inner crust is almost completely pulverized.
Other evidence shows that the Moon's crust is thinner than previously thought.
"Using GRAIL gravity data, we found an average crustal thickness of 32-34 km, which is 10 km less than previous studies," said Mark Wieczorek, co-investigator at GRAIL. "We found that most of the aluminum on the Moon is almost the same as on Earth. This relates to the recent hypothesis that the Moon came from material from the Earth when it formed during a giant impact."
NASA's GRAIL mission captured video as it flew over the pool Mare Orientale on the Moon. The video was obtained using MoonKAM on board the spacecraft GRAIL's Ebb April 7-8, 2012. Credit: NASA/JPL-Caltech/Sally Ride Science.
During the main mission, the two GRAIL spacecraft were in orbit 55 km above the lunar surface. This close range was because GRAIL produces the best gravitational field data for any planet, including Earth.
"GRACE is still collecting data, but since GRACE must be in an orbit at an altitude of 500 km," Zuber said. "Nothing beats low orbit."
Zuber said the GRAIL team learned from GRACE and was able to make "some reasonable improvements." They also suggested that this technology should be used for every planetary body in the solar system, and threw out a tantalizing idea: "Visualize, map the currents underneath."
GRAIL ends its primary science mission in May 2013 and is currently operating on an extended mission where the spacecraft's altitude has been lowered to 23 km above the surface. "We're opening a window in terms of geophysics, and so you'll hear results from the new data set soon," said Sami Asmar, a member of the GRAIL team.
At the Astronomical Geophysical Union conference, Zuber said that on December 6, 2012, the team will lower the spacecraft to 11 km above the lunar surface.
Artist's concept of the GRAIL mission, with two spacecraft in tandem orbiting the moon to measure the gravitational field in unprecedented detail. Credit: NASA/JPL.
The extended mission will end soon, in mid-December, and shortly thereafter the two spacecraft will be deliberately destroyed on the lunar surface. The team said they are still formulating ideas for the strike scenario, and are looking at the possibility of targeting the strikes as they are within the field of view of the instruments on .
0The Moon and its relationship with the Earth and the Sun have been studied by humanity from ancient times to the present period more and more intensively and successfully. The fruits of this research, up to and including recent years, are presented in many monographs and textbooks. It is beyond the scope of this paper to review previous studies, and in this discussion we will refer the reader to them without going into detail, and only when the most recent data are discussed. The lunar surface consists mainly of many craters that were created as a result of collisions with giant meteorites. This particularly applies to the invisible side of the Moon and the continental regions on its visible side. The large circular seas: the Sea of Rains, the Sea of Clarity, the Sea of Crisis, the Sea of Nectar, the Sea of Humidity and the Eastern Sea - are formed as a result of collisions with huge meteorites, and the shallow, irregular seas consist of flooded areas with igneous material covering proto-continents similar to modern continents regions. These shallow seas have mountain ranges that appear through the dark, smoothed material, and may cover areas that are "impact" seas, the outlines of which have been erased by subsequent events. If such collisions occurred on Earth (which seems inevitable), all terrestrial rocks that existed before the collision would turn into clastics. Since igneous and sedimentary rocks have been preserved on the earth's surface for 3.5 eons, such numerous collisions must have occurred at an earlier time period. Radiated craters (often small in size) and a number of large craters without rays undoubtedly formed in all geological epochs of time. Large seas take the form of lava flows, or volcanic ash, or water lakes.
This is, of course, not true, as evidenced by the absence of water in lunar rocks, but the choice between other possibilities remains open. There are also endogenous explosion craters, and some scientists believe that calderas exist on the Moon. The author of this chapter doubts the presence of large calderas on the Moon. The physical constants of the Moon and its orbit are well known. Some of them are shown in the table.
GRAVITATIONAL FIELD OF THE MOON
The gravitational field of the Moon has been studied in great detail using lunar orbiting satellites. It has been established that this field can be represented by ordinary series in spherical harmonics only when using a large number of terms. Michael and co-workers have compiled the most detailed tables for the constants contained in Eq.
The authors point out that for a mathematical description of the gravitational field, terms up to the 13th order are needed, and even in this case the constants do not decrease, which indicates that the gravitational field of the Moon is far from what we expected to obtain by studying the motion of a small body in field of gravitational forces of the Earth, Moon and Sun, taking into account the centrifugal forces of rotation. In the latter case, the terms following C 2.0 should be equal to zero, which is not true. From this it follows that the distribution of masses inside the Moon is very uneven.
where A, B and C are the moments of inertia: A - relative to the axis directed to the Earth, B - relative to the east-west axis and C - relative to the polar axis, were carefully studied by Koziel, who, according to lunar librations, found them respectively equal to 3.984 * 10 -4 , 6.294*10 -4 and 2.310*10 -4 . Kopal obtained very similar values for the same constants. Theoretical values for a plastic Moon under the influence of tidal and centrifugal forces turn out to be equal to 0.94 * 10 -5, 3.75 * 10 -5 and 2.81 * 10 -5. This again indicates that the Moon is a very solid body and has been so since ancient times. Estimates of the values of the moments of inertia show that they are close to 0.4 Ma 2, where M and a are the mass and radius of the Moon. This value is typical for a ball of uniform density. Of course, the surface regions of the Moon to a certain depth consist of low-density matter and should somewhat reduce the values of the moments of inertia. These low-density areas are located mainly on the far side (possible thickness 30 km) and are responsible for the irregular shape of the Moon, moments of inertia and a displacement of the center of mass by 2-3 km relative to the center of the figure.
The triaxial ellipsoidal nonequilibrium shape of the Moon has long been a mystery to scientists. Various explanations for this phenomenon have been proposed.
1) The Moon may be a fairly solid body capable of maintaining a non-equilibrium shape, but this does not explain its origin.
2) Lower temperatures at the poles would lead to a higher density of matter and smaller radii in these regions, but this does not explain the difference between the moments of inertia A and B.
3) Convective currents in the Moon, rising at the poles and descending at the equator, should have led to a decrease in mass at the poles and an increase in mass at the equator, but again in this case the moments of inertia A and B should be equal. It is possible that a certain combination of the second and third hypotheses of a very specific type is being realized.
4) The Moon accumulated from bodies of different densities, which explains the differences in the moments of inertia. If convective processes had taken place, then the Moon at some period of its formation should have been almost completely molten, since, according to Chandrasekhar, two-cell convection is possible only with a small core. Convection on the Moon must be so deep that, unlike the Earth, folded mountains do not form on it. Booker advocates single-cell convection, which would result in a higher altitude on the invisible side of the Moon if the updraft were on the visible hemisphere.
Müller and Sjogren showed that in various regions of the visible side of the Moon there are significant accumulations of masses, called mascons, in most cases associated with circular maria of impact origin and, probably, in all cases associated with the existence of certain localized masses. These mascons were discovered and mapped based on observations of artificial lunar satellites and by directly measuring their speeds. Müller and Sjogren believe that the observations are reliable for longitudes between 100 and -100° and for latitudes between -50 and 50°. Noticeable positive gravity anomalies in the Seas of Rain, Clarity, Crisis, Nectar and Humidity are reliable, as well as a positive anomaly noted slightly northwest of the center of the lunar disk. The Eastern Sea is an example of an anomaly that is partly positive and partly negative. Other positive and negative anomalies are likely within the limits of observational error. The negative anomaly in Rainbow Bay is regarded by the authors as a real phenomenon. They also detected negative anomalies in the Ptolemaic and Al-Batani cirques measuring 87 milligal as observed by the Apollo 12 spacecraft as it approached the landing site. Booker and others have estimated the amount of excess mass required to obtain on the order of 100 bar. Since these formations are ancient, gravitational anomalies should persist on the Moon for several eons, indicating that the Moon is and was a body of very high hardness. Two ways to explain these phenomena have been proposed.
1) It is assumed that the substance of the lunar interior, due to various processes, rose to the surface in recesses formed as a result of interaction with objects responsible for the formation of seas.
2) It is believed that mascons consist of the remains of the colliding foreign objects themselves, together with the main substance, filling the recesses formed as a result of the impact collision.
If the basis for the formation of mascons is considered to be lava flows from the depths of the Moon, then it must be borne in mind that to create such deposits an excess pressure of about 50-100 bar is required. There are no sources of such pressure on the Moon. It is possible that the substance flowed into the huge recesses formed as a result of enormous collisions from surrounding areas. It is likely that Van Dorn waves in the highly crushed surface layer of the Moon could cause such a process, but then special assumptions are required to explain the excess mass per unit surface. The excess mass can be explained if lava flows from under neighboring areas into sea areas. Recently, Sjögren concluded that the additional mass of the Sea of Serenity is contained in a near-surface plate that could have been formed by such lava flows.
According to another hypothesis, the rocks of the lunar interior moved as solid matter into gigantic cavities formed at the moment when the seas appeared; the rocks had a higher density than most surface rocks. If they moved until isostatic equilibrium occurred, gravitational anomalies would not exist. If isostatic equilibrium is not achieved, negative anomalies would appear. If the boundary of isostatic equilibrium were crossed as a result of a large amount of movement of rising matter, or the mass were increased by a flow of lava or fragmented rock, a positive anomaly would occur. In this case, it should be assumed that in an extremely fragmented
Enormous stress would develop in the underlying rocks. This explanation is possible, but unlikely.
It is generally accepted that the outer parts of the Moon endure significant stress and that heating within the Moon results in the creation of a molten mass that is squeezed out into the sea basins. This partial melting on Earth produces rocks that are less dense in their solidified state (and even less dense in their liquid state) than the rocks from which they are formed. On Earth, lava flows form mountain ranges with positive gravity anomalies. On the Moon, the lowlands of the seas are filling. Perhaps high-density titanium-iron basalt could be such a substance. However, numerous cracks and grooves on the lunar surface do not support the hypothesis that the outer shell of the Moon can withstand great stress.
Such a mechanism for the formation of rocks on the lunar surface involves a net ejection of rocks equal in volume to the product of the area of the seas at a depth of about 50 km, and this should inevitably lead to the formation of a layer of ejected rocks 1/10 of this thickness over an area 10 times greater than the area of the Mare Monsim and Seas of Tranquility. The author of this chapter, based on available photographs of the lunar surface, doubts the validity of this point of view.
The hypothesis that mascons are the remnants of foreign objects that collided with the Moon is based on a number of assumptions, namely that the impact occurs at a speed only slightly greater than the escape velocity for the Moon, that the characteristics of the impact can be extrapolated based on the energy parameters of the nuclear explosions and in the case of lunar maria, and that the volume of the net “ejection” of lunar rocks is equal to the volume of the object colliding with the Moon. This explanation implies a kind of “filling in.” Due to the difficulty of preserving mascons, if the interior of the Moon is at the melting point of the rocks, it is assumed that the filling occurred during the impact, through the processes described by Van Dorn. It is important that there is an approximate correspondence between the masses required to form mascons and the masses necessary to form seas. The large excess mass of the Mare Mons mascon and the mascons of other seas and their continued existence for eons (probably 4.0 * 10 9 years) indicate that the Moon is and was a more solid body and with lower temperatures than the Earth, at in which isostatic equilibrium is established within approximately 10 7 years. It seems that the hypothesis of colossal lava flows and very large movements of matter from the inner zone of the Moon is not consistent with the preservation of these massive structures over several eons.
Interestingly, the laser altimeter of the Apollo 15 spacecraft showed that there were large differences in altitude for different parts of the lunar surface. The regions of the visible hemisphere, generally speaking, lie lower by about 2 km, and the invisible hemisphere is elevated relative to the sphere centered at the center of mass. In addition, the deeper points identified so far are located in circular seas, which, of course, means that some masses of high-density matter must lie under the surface of these regions. On the invisible side of the Moon there is also a very deep Van de Graaff crater with irregular outlines, and the question naturally arises about the existence of a mascon in this area.
SURFACE OF THE MOON
The lunar surface is covered with craters and vast, flat areas. The craters are predominantly of impact origin, but, of course, there are also volcanic ones. Impact craters range in size from microscopic to gigantic lunar maria areas hundreds of kilometers in diameter. The areas are of different ages. The old, very densely cratered areas are probably between 4.0 and 4.6 billion years old. Isolated, rare craters cover areas that have been formed throughout geological time. These craters have been studied by many researchers with great care. However, they mostly represent random events and reveal little about the history of the Moon. Ptolemy and Al-Batani have negative gravity anomalies of approximately 87 milligal and thus indicate that these old craters arose on the solid Moon early in its history and that the solid state has persisted to the present day. Unfortunately, it is difficult to say exactly what temperature regime is consistent with this fact. Large craters have central peaks, indicating that there was a "ricochet" of material or that there is a fragment of a foreign body that hit the Moon. Probably the first explanation is more correct.
There are also volcano-like craters on the Moon. These include craters surrounded by dark areas and a series of craters along winding chasms. Davy's Fissure consists of a nearly straight line of craters that may be endogenous or impact craters caused by impacts with objects such as the head of a comet, which were broken into many fragments by the gravitational field of the Moon. In many cases it is difficult to tell whether other small craters belong to this class. Solving this problem required significant efforts. Many of these craters have wide mouths, as if they were created by the outflow of gases. (Steam is the most characteristic volcanic gas on Earth! What are these gases on the very dry Moon? Did water react with iron somewhere in the inner zone to release hydrogen, or was it carbon monoxide, or something else?) In some Local structures of lava flows are observed in places, especially in the Mare Monsim and in the Sea of Serenity. In addition, the Maria Hills, located in the western equatorial region, appear to have signs of volcanism.
Great seas are vast vents that are commonly thought to be lava, but which may be volcanic ash or pyrogenic rock. Lava streams emerging on the surface of the Earth are usually foamy, and streams emerging on the lunar surface, where at least at present there is a deep vacuum, should be the same, even if the molten masses contain less volatiles. What is now observed are soils consisting of finely crushed crystalline and glassy particles in which fragments of crystalline rocks are immersed. These fragments sometimes have cavities with smooth walls, which should be formed during the crystallization of a molten mass containing macroscopic gas bubbles. They appear as if they had hardened at some depth beneath the insulating surface layer. Collisions of micrometeorites with soil and stones played a role in the formation of the soil, although it is probably partly of pyrogenic origin.
Large shallow seas - the Ocean of Storms, the Sea of Tranquility, the Sea of Plenty and the Sea of Clouds - do not have noticeable gravitational anomalies that coincide with them. Thus, the streams are in a state of isostatic equilibrium, indicating that the material of the streams probably comes from below the surface where it lay, or that isostatic equilibrium has been established for large areas of the surface, but not for mascons lying on some depth below the surface. This layer of dark rocks must be very thick, on the order of several kilometers, because the mountains of impact origin, which were originally located in these areas, are mostly covered by the mentioned flows. These rock formations could have been partially destroyed as a result of powerful impact processes that led to the appearance of large seas, but in shallow seas there must also be deep “pockets” and shallow areas. For many years, a common hypothesis was that these dark seas were formed by lava flows from the interior of the Moon; this hypothesis remains popular today. However, seismic data differ so significantly from data recorded on Earth that to explain these discrepancies it is necessary to postulate marked differences in surface structures. The best explanation that has been proposed at the time of writing is that the lunar surface is composed of extremely fragmented material and consists of soil with rocks scattered in it (see discussion below).
Estimates of the thickness of the regolith vary significantly. Shoemaker et al. indicate small values of this value, ranging from 3 to 6 m depth in a crater near the landing site of the Apollo 11 lunar compartment. Kopal, based on the depths of the grooves, insists on a thickness of several hundred meters, and Seeger, based on a study of the structures of the Davy crater, believes that the thickness of the layer at this point is 1 km. Gold and Souter suggest that the depth of the layer of fragmented matter is 6-9 km. These estimates refer to the surface layer of the seas. Intense impact processes on the surface of the continents should also have led to the formation of highly fragmented matter, and, of course, the surface of the continents was subjected to the same bombardment of micro- and macro-meteorite objects (as the surface of the seas) from the moment of their formation.
Large large seas were formed as a result of collisions with massive bodies. Van Dorn applied wave theory to study such impact collisions and, in particular, in the case of the Eastern Sea, noted good agreement between the calculated and actual radii of wave-like structures surrounding this and other seas, assuming the existence of a liquid layer 50 km thick. However, it is impossible to assume simultaneously the existence of a liquid layer 50 km deep and at the same time a solid crust supporting the existing mountain ranges. It is possible that a highly fragmented layer of solid material could behave like an imperfect liquid, forming waves under high-energy processes that solidify once the energy density drops to lower values.
Kaula et al. showed that the far side of the Moon is higher than the visible side by about 3-4 km and that the center of the figure is shifted to the longitude 25° E by 2-3 km. This probably indicates a crustal thickness of about 30 km on the far side and that the crust is composed of minerals rich in CaO, Al203 and Si02, and contains some FeO.
Physical data on the lunar surface indicate that on the surface of the seas and continents there is a highly fragmented layer of silicates, that the body of the Moon is very solid down to significant depths and was so for most of the time of its existence.
SEISMIC OBSERVATIONS
Seismic instruments were installed on the lunar surface by members of the Apollo spacecraft crews, and the information obtained with their help is of great value in understanding the internal structure of the Moon. The first, most surprising discovery was that the attenuation rate of seismic signals on the Moon was much less than the attenuation rate on Earth. The lunar compartment of the Apollo 12 spacecraft fell onto the lunar surface at a speed of 1.68 km/sec. The impact energy was 3.36 * 10 16 erg. The distance between the crash site and the nearest seismometer is 73 km. A signal was recorded that reached a maximum after approximately 7 minutes. after impact, and then slowly faded away
for 54 min. When the launch vehicle of the Apollo 13 spacecraft was dropped onto the Moon (velocity at the moment of impact 2.58 km/sec, impact energy 4.63 * 10 17 erg, distance from the seismometer 135 km), a similar phenomenon was recorded that lasted over 200 min. If the speed of sound were 6 km/sec, the sound waves would travel 21,600 km, or 6 times the diameter of the Moon, in 1 hour. Both P and S waves were recorded (both a compression wave and a shear wave). Similar phenomena were recorded in the most recent flights.
These results differ significantly from observations on Earth, where the signals would fade away within minutes. Other, weaker signals of an almost similar type were observed, probably as a result of meteorite bodies falling onto the lunar surface. In addition, other groups of signals were received in which the registration pattern was very accurately repeated, indicating that the members of the group of signals originated from the same source and went to the seismometers along the same paths. The waves and energy of long-period oscillations are concentrated in a very small volume, probably in the surface layer, mainly in the immediate vicinity of the source. Such slow decay of signals is not observed on Earth, and therefore there must be significant differences in the physical characteristics of the two planets. The most obvious of these is the more fragmented nature of the lunar surface. It is likely that both the Ocean of Storms and the Sea of Tranquility should have a highly fragmented layer, similar to that found on parts of the continents that lie under the dark soil and rocky layer of the seas. Latham et al. discussed its structure, and Gold and Sauter carried out calculations using a model of a dust layer several kilometers thick with sound speeds increasing linearly with depth and with reflections from the outer layer of the sea surface. The two models are similar if we remember that rocks smaller than the wavelength have little effect on the propagation and reflection of sound waves. It's likely that solid silicate layers would behave differently.
A number of signals are reproduced with high accuracy and cannot be attributed to meteorites; therefore, they are of an endogenous nature. They are more often recorded at perigee and, apparently, are “turned on” by the tidal effect. Reflections from various masses and surfaces should occur. Consequently, there must also be extensive structural inhomogeneities. These "moonquakes" mean that mechanical or potential energy from a number of sources is dissipated as vibrational energy and heat. One can imagine several sources of such energy.
1) Mascons dive into deeper layers.
2) The irregular shape of the Moon turns into a more regular spherical shape.
3) The ellipsoidal lunar orbit becomes increasingly circular as the major axis decreases. This effect could be layered on top of other orbital changes due to other reasons.
4) Convective processes in the bowels of the Moon or lava flows cause “Earth-like” moonquakes.
5) As the Moon moves away from the Earth due to tidal effects, it, remaining one hemisphere facing the Earth, reduces its rotation speed, and this probably causes moonquakes, and the rotation energy is a source of seismic energy.
6) Slight contraction and expansion occur due to temperature changes on the Moon.
7) Stone slides. However, it seems likely that this process took billions of years to complete.
"Moonquakes" appear to occur at depths of about 800 km, and reflections occurring at such depths indicate that some layered structure exists at these depths. However, there is no reliable evidence of the existence of a metallic core yet. There may be a basaltic 20 km layer of regolith; to a depth of 60 km - a layer with a compression wave speed equal to the speed of sound in anorthosite, and. deeper, at an indefinite depth, is a material with the speed of sound characteristic of dunite. Thus, the layered structure probably consists of a 20 km layer of fragmented basalt, a 40 km layer of anorthosite and then a layer of dunite of unknown depth with a moonquakes source and weak reflection at a depth of approximately 800 km; There is no evidence of the presence of a metal core. Recent data show that there is a central region that does not conduct S" waves
and probably consisting of partially molten silicates. This central "core" has a radius of about 700 km.
The Moon is much quieter than the Earth with its inexhaustible sources of energy, the most important of which is convection in the mantle caused by radioactive heating. It is this that creates giant mountain ranges, positive and negative gravitational anomalies, gives rise to huge volcanoes and lava flows, and moves continents. If convection exists or existed on the Moon, its effects should be very small compared to what is observed on Earth.
The explanation of seismic phenomena as a consequence of a fragmented layer on the surface fundamentally contradicts the idea of a layer of solidified lava beneath the surface. In contrast, the lunar soil contains rocks that were formed by melting, and complex and carefully studied patterns of “moonquakes” indicate the existence of complex structures beneath the lunar surface.
CHEMICAL COMPOSITION
The most recent measurements of the radius of the Moon made it possible to establish the average density of its soil as 3.36 g/cm 3 , and the sharply fragmented nature of the surface layer indicates that when estimating the density of matter for the entire Moon, the influence of voids must be taken into account. In addition, the density of the subsoil may decrease due to high temperatures to a greater extent than increase due to high pressures. This again indicates that mineral densities may be higher under laboratory conditions. Perhaps the value of 3.4 g/cm 3 is an acceptable estimate for the average value of this parameter. The average densities of type L and H chondrites under low pressure conditions are in the range of 3.57 and 3.76 g/cm 3 or 3.68 and 3.85 g/cm 3 if heavy minerals are present. The density of earth's soil at low temperatures and pressures can be about 4 g/cm3. Consequently, the Moon contains either less iron or larger amounts of water and carbon compounds than Earth's rocks. The low contents of water and carbon compounds in the surface material contradict the second hypothesis. Silicates, as shown by analysis of meteorites with an iron content of no more than 10 weight percent, could provide the required density. Type III carbonaceous chondrites also have this density. The concentration of potassium in these meteorites is lower than in other chondrites, being about 360 ppm instead of 850 ppm. This lower relative abundance of potassium, and comparable concentrations of uranium and thorium, would have allowed the initially cold Moon to remain below the silicate melting point throughout geological epoch.
Wencke, in a very comprehensive review of the chemistry of the Moon, came to the conclusion that the surface material of the Moon can be considered as a mixture of two components: one condensed at a high temperature and the other having an average meteoritic composition. The ratio of K to U is about 2000, while in chondritic meteorites it reaches 60 or 80 thousand. This is due to the significantly increased concentration of U and other elements that condense at high temperatures. Interestingly, this ratio for terrestrial rocks is approximately 10,000, indicating an increased proportion of high-temperature condensate in the Earth.
The first data on the chemical composition of lunar rocks, obtained by Turkevich et al. based on observations using the Surveyor 5 - Surveyor 7 spacecraft, indicate that the surface of the seas contains basalt with a high content of titanium and that the continents have high concentrations of aluminum and calcium and low concentrations of iron. These results were fully confirmed later by a more detailed study of the composition of lunar rock samples delivered to Earth by the crews of the Apollo spacecraft. There are several different types of rocks on the lunar surface. The marine areas appear to consist predominantly of basalt-type rocks and finely crushed material. Continental areas are made of rocks characterized by high concentrations of calcium feldspar, substances such as anorthosite. Further, the area near the Fra Mauro crater, where the crew of the Apollo 14 spacecraft “landed,” consists of what we call KREEP, i.e., a substance characterized by a high content of potassium, rare earth
elements and phosphorus. Anorthosite or KREEP type meteorites have never been observed, and no other lunar rocks are found among meteorites. Other types of rocks have been discovered that are apparently rare.
There are some noticeable differences in the chemical composition of lunar, terrestrial and meteorite substances.
A very curious difference in chemical composition concerns europium. This element is divalent in highly reducing environments and trivalent in less reducing conditions. In lunar surface rocks, europium shows a clear tendency to follow divalent strontium and a weakened tendency to behave like other trivalent rare earth elements. This shows that the lunar surface rocks formed under highly reducing conditions. Only small metallic inclusions of iron and nickel are detected, and it is still unclear whether they are of lunar origin or fragments of meteorites. Iron sulfide is found only in small quantities. Most surprising is the fact that the concentration of titanium is much higher in some lunar basalts than in terrestrial ones.
The physical properties of these silicate rocks are interesting. Basalt soils consist of very small crystalline and glassy fragments. The breccias appear to be sintered soil. There are rocks that have crystallized from a liquid melt and sometimes contain smooth bubbles, indicating that gas bubbles were present during the solidification process. "Creation Specimen" 15,415 consists entirely of vitrified calcium feldspar spherules. Moon rocks often contain round silicate inclusions, which have physical properties similar to meteorite chondrules, but have a different chemical composition. However, no identified meteorite fragments have been found, indicating that meteorites that impact the Moon are broken into extremely small fragments. In addition, lunar rocks differ in chemical composition from meteorite rocks.
Because the Moon does not have an atmosphere, high-energy radiation can be observed emitted by radioactive elements at high altitudes above the lunar surface. Such observations were planned by Arnold when drawing up the program of flights to the Moon and were recently successfully carried out by members of the crews of the Apollo 15 - Apollo 17 spacecraft. These studies indicate that marine areas have higher concentrations of potassium, uranium and thorium than continental ones, and that different concentrations of these elements are recorded over large areas of the sea surface. In addition, the potassium/uranium concentration ratio is always lower than in terrestrial rocks. These data are confirmed by analysis of lunar rocks brought to Earth and show that large areas of the Moon's surface are characterized by chemical differences. Adler et al., studying the X-ray fluorescence of lunar rocks when illuminated by solar X-rays, showed that continental areas, generally speaking, contain more elements characteristic of anorthositic rocks. Unfortunately, more detailed and extensive studies of this kind covering the entire surface of the Moon have not yet been carried out.
It seems probable that from the earliest stage of the Moon's existence there was continuous melting on a limited scale; This appears to be confirmed as the study of lunar samples expands. Small lava flows found in various places may be of more recent origin. If they emerge from the deep interior of the Moon, they can provide information about the chemical composition of the deep interior, which will be very valuable. It was thought that the crew of the Apollo 16 spacecraft landing near Descartes Crater would find more recent volcanic rocks, but the site turned out to be covered with ancient anorthosite rocks. The crew of the Apollo 17 spacecraft must land in a dark bay in the Mare Serenity, near the Littrow Crater, where there are very clear signs of a lava flow. If this stream came out from a shallow depth, then the question arises: how could a large mascon survive in the Sea of Clarity, since the bowels of the Moon in this case should have had a high temperature, starting from the local source of the specified dark rock and to great depths? It follows that the volcanic flow, if there is one, came from deep within and that the Moon has a very hard outer shell. Rock samples delivered from this site will provide information about the composition of the lunar interior.
CARBONIC SUBSTANCES
No evidence has been found to support the existence of living or fossil biological forms on the Moon. Total carbon concentrations in all lunar rock samples studied range from 30 to 230 parts per million, with carbon concentrations in the soil being higher than in crystalline rocks. The concentration of nitrogen is slightly lower than that of carbon.
Chemical analysis confirmed the presence of hydrocarbons, compounds of carbon, hydrogen, oxygen and nitrogen, but in general in such small concentrations that it is difficult to be sure that they are endogenous substances and not a consequence of terrestrial pollution. The gas chromatograph and mass spectrometer are so sensitive that they can detect some contaminants in concentration ranges as low as 10 -9 . All researchers found various hydrocarbon compounds containing up to six or more carbon atoms, and the more common and simple compounds of carbon with oxygen, hydrogen and nitrogen. The most interesting compounds from the point of view of the existence of biological forms of matter have been identified by a few researchers. Nagy et al. discovered glycine, alanine, and ethanolamine in addition to urea and ammonia. Fox et al. found glycine and alanine in non-hydrolyzed aqueous extracts and, in addition, found the presence of glutamic acid, aspartic acid, serine and threonine in extracts after hydrolysis. The concentrations of these substances were about 50 parts per 10 9 . Hodgson et al. identified porphyrin, but they associated its presence with contamination of lunar rocks by rocket engine nozzle gases. Bearing in mind the very small amounts of detected substances, it is necessary to prove the content of these compounds in other samples of lunar soil and to take samples for analysis with special care, avoiding their contamination. It is likely that many compounds were formed by adding chemical solutions to the studied samples of lunar rocks, because lunar rocks contain activated atoms of carbon and other elements that fell on the surface of the Moon with the solar wind. Abell et al., in particular, proved the formation of deuterium methane C D 4 when using deuterium water D 2 0 instead of ordinary water H 2 0. Water in moon samples
of soil is contained in such small concentrations that it is extremely difficult to distinguish between endogenous water and terrestrial pollution.
AGE OF THE MOON
When studying the age of lunar rocks, two methods of determination are used. Assuming that the lunar rocks originated from meteorite-type substances, the time is determined when the rocks of the lunar surface were separated from the substance of meteorite origin. This time is known as “model age”. When calculating Rb 87 - Sr 87 ages or uranium-lead and thorium-lead ages, it is assumed that the concentration ratios of rubidium to strontium or uranium and thorium to lead have not changed since the separation. The second method of determining the age of rocks determines the time when the sample under study was last in a molten state or when the isotopes of elements were last evenly distributed between the minerals of the rock sample under study. This is an "isochronic age". Rb 87 - Sr 87 model age for most of the studied lunar soil samples is about 4.6 eons (4.6 10 9 years); this is the time required for the formation of Sr 87 in most samples from primordial strontium in 4.6 eons, according to studies of basaltic achondrite meteorites. The isochron ages of the rocks vary from 3.3 to 4.1 eons. This means that the general composition of the rocks in relation to rubidium and strontium was formed in this form 4.6 eons ago and did not change during the process of repeated heating that took place at later isochronic moments. Ash flows in these later periods did not lead to the separation of liquid melt and solid residues, which was probably due to the weak gravitational field of the Moon, in which pockets of partially molten masses did not separate into layers consisting of liquid and solid phases, or was caused by complete melting of basalt pockets, so that fractionation did not occur. By 40 -Ar 40 the age is generally consistent with the Rb 87 - Sr 87 isochronic age, since argon dissipated in the very last heating phase. Uranium-lead and thorium-lead ages of the rocks give a more complex picture and are not consistent with Rb 87 - Sr 87 ages, apparently due to loss of lead into the surrounding space, probably due to volatilization. It is interesting to note that the isochron ages of a large number of the studied soil samples and many crystalline samples have values in the range of 4.3-4.6 zones.
Because the soil samples and rocks have different compositions, volcanic flows erupting from isolated pockets should not have mixed with each other in the period from 4.6 eons ago before the formation of the flows, i.e. 3.3-4.0 eons ago. Whether the outpourings occurred before 4.0 eons or after 3.3 eons is unknown. The opposing hypothesis is that the basaltic components were formed by ordinary terrestrial flows in which the basaltic melt was separated from the solid fraction remaining at depth, and that uranium-lead, thorium-lead, rubidium and strontium in varying quantities were added later from some primordial matter formed 4.6 eons ago. In this case, it must be assumed that these original basaltic rocks with low contents of these elements were formed as a result of melting processes, during which, in the case of terrestrial rocks, as a rule, basalts containing the mentioned elements are formed. However, this is completely incredible, and a more reliable explanation, apparently, is that the cause of the discrepancies was the melting of limited systems in the presence of a weak gravitational field.
Two age indicators are of interest: determined by the ratio K 40 - Ar 40 (method developed by Turner) and determined by the ratio Rb 87 - Sr 87 (method developed by Schaefer et al.). Creation sample 15415 and the anorthosite rocks brought back by the crew of the Apollo 16 spacecraft are about 4.1 eons old. It has been suggested that the age of some anorthositic rocks should be 4.6 eons on the basis that the earliest period of melting occurred at that time and that the anorthositic rocks appeared then. What shifted the clock of the cycle K 40 - Ar 40? A hot sun, collisions in the asteroid belt, or both, or something else unknown?
HISTORY OF THE MOON
It is now known that the continental regions of the Moon consist of rocks of the anorthosite type and that these rocks and titanium-iron basalt acquired their composition as a result of melting processes 4.6 ± 0.1 eons ago. Later melting occurred, leading to the formation of the rocks of the Sea of Tranquility and the Ocean of Storms. As a result of some processes during this period, mascons were formed and, due to the hardness of the rocks, have been preserved to the present day. The maximum subsurface temperatures required to preserve the mascons are not known, but the Earth's subsurface temperatures appear to be too high. An accurate comparison is made difficult by the Earth's greater gravitational field and higher pressure in its outer layers. If there was no evidence of melting, one might assume that the Moon has been cold throughout history. If it were possible to ignore the mascons, this would lead to the acceptance of the high-temperature hypothesis, of course, ignoring or finding another explanation for the moments of inertia. If all circumstances are taken into account, it becomes inevitable to recognize the need for a complex history of the Moon. If anything, magnetic stones are mysterious.
If the Moon was originally completely molten, then it must have solidified and undergone differentiation 4.5-4.7 eons ago. The anorthosite layer hardened and floated to the surface, the pyroxene-olivine layer sank into the depths, and the layer of titanium-iron basalt appeared between them or mixed with other layers to be released later during the subsequent melting of individual volumes. The outer parts must have cooled to such an extent as to ensure the persistence of negative gravity anomalies in the Ptolemy and
Al-Batani and, probably, in such craters throughout the surface. This happened when the concentrations of radioactive elements were at their maximum levels. Much research has been carried out on the thermal regime of the Moon throughout its geological history. Such studies show how difficult it is to cool the molten body of the Moon within an eon, even in the absence of radioactive elements. Perhaps, as Tozer emphasizes, convection played the largest role. In the case of the Earth, cooling has not occurred for 4.6 eons and positive gravitational anomalies are maintained only by giant convective cells. Throughout the appearance of lava flows, the interior of the Moon must have maintained a high temperature, and only in the outer shell was it possible for the existence of solid rock, as is the case with the Earth. It seems unlikely, if not downright impossible, to explain the observations in this way. Even without resorting to mascons, such a hypothetical lunar history would produce more numerous lava flows than are actually observed, and especially such a high-temperature hypothesis would involve much more extensive melting of the lunar surface. The absence of marine-type areas indicates that melting processes had only a small extent.
If the values of the moments of inertia established using artificial lunar satellites and astronomical observations are correct, then an extended layer of low-density anorthositic rocks, a small iron core and dense silicon rocks in the interior of the Moon are unthinkable without the existence of some layer of high-density matter near the surface. And it seems incredible that such a layer of rock with a high density of matter would have formed and been preserved if the Moon had been an entirely molten body at an early stage of its existence. But perhaps the data on the moments of inertia are incorrect!
It has been suggested that the initial melting 4.5-4.7 eons ago was limited to the outer layer in the initially cold Moon and that the mascons were supported by the cold interior, and the negative gravity anomalies of the Ptolemy and Al-Batani craters and other craters - the outer layer, which cooled down pretty quickly. This model assumes that the following factors were the sources of heating.
1) Surface heating in a large gas sphere or during the process of accumulation in such a sphere.
2) Surface heating due to tidal effects during the capture of the Moon.
3) The movement of magnetic fields along the lunar surface and the excitation of electric currents in silicates already heated by some previously operating mechanisms.
4) Heating during the accumulation process, in which rapid accumulation of solids occurred in the last stages. As it cooled, it separated into several layers, with the titanium-iron basalt solidifying last, somewhere below the surface. Apparently, option 4) would lead to the creation of very dynamic conditions, poorly suited for separating rocks into the various layers identified by chemical research. The basalt melted later and was forced upward from deeper layers. Radioactive heating may have occurred as a result of the very low thermal conductivity of the dust layer on the surface and its high thermal insulating properties. "Shallow" seas, consisting of ash flows on a highly irregular surface, would have several deep-lying layers as well as surface layers. The deep layers must have warmed noticeably over periods ranging from hundreds of millions to a billion years, even if they initially had low temperatures (about 0 ° C), which, however, is not at all necessary. The author of this work shares these ideas.
It was previously believed that the first craters, maria and mascons were formed as a result of collisions in the early stages of the geological history of the Moon, but if we assume that a catastrophic collision occurred in the asteroid belt about 4 eons ago, leading to the formation of many large and small fragments that fell on the Earth, the Moon and other planets over several hundred million years, it is possible to construct a different history of the lunar surface. There are no traces of such collisions preserved on Earth if they occurred before the formation of the most ancient rocks of the Earth. We must accept that the mascons arose as a result of some "ricochet" of lunar rocks and that gravitational anomalies persisted despite extensive and energetic displacements of rocks, since collisions of this kind must have occurred at high speeds.
Therefore, to explain gravitational anomalies, the masses of objects colliding at such high speeds must be extremely small. With this assumption, we can easily have the Moon's surface cold enough to support the presence of gravitational anomalies of the Ptolemaic and Al-Batani type, but the problem of the existence of mascons remains unresolved if we accept that titanium-ferruginous basaltic rocks poured onto the surface from a subsurface melt, which seems to be an acceptable hypothesis with this understanding of the early history of the Moon.
Partial melting of the lunar interior 3.1-3.0 eons ago, as is accepted by some researchers, would almost certainly lead to the separation of rubidium and strontium from each other, and, therefore, the model age of titanium-iron basalts almost certainly could not be about 4 ,6 eons. This is a weighty argument against the formation of these rocks as a result of partial melting of the lunar interior.
Thus, we can conclude that the Moon formed at relatively low temperatures, was heated by external heat sources, cooled sufficiently and to a sufficient depth to allow large craters (150 km in diameter) to maintain negative gravitational anomalies, and was, thanks to its solid interior, capable of maintain mass concentrations. Differentiation of anorthosite, titanium-iron basalt and other fractions occurred during the cooling process. The soil was formed primarily from an ash flow and was melted in limited quantities due to radioactive heating due to the low thermal conductivity of the surface layers of the soil. This alleged history is complex and will likely be revised as evidence accumulates.
As discussed above, seismologists have obtained data confirming the existence of an anorthosite layer extending to a depth of about 60 km below the surface, and an internal zone below this layer consisting of dunite-type rocks rich in pyroxene and olivine. Compared to earthquakes, moonquakes are very moderate, and some of them occur repeatedly at points located at a depth of about 700-800 km. In this case, reflections occur in structures located at approximately the same depth. They cannot be caused by the existence of a metallic core, but can be created by the interfaces of structures of some other type. This supports the hypothesis of very deep or complete melting at the dawn of lunar history. However, the evidence is not conclusive. Observations were carried out on limited areas of the lunar surface and in areas relatively close to the zones of large mascons and impact seas.
MAGNETIC STONES OF THE MOON
No dipole field has been discovered on the Moon, but magnetized rocks are located at the Apollo landing sites, which are between 4 and 3.1 eons old. Therefore, before this or later time, magnetic fields must have been present on the Moon, and rocks in these magnetic fields must have cooled to temperatures below the Curie point. There are also quite large magnetized areas. The origin of the magnetic fields responsible for the formation of magnetized stones remains a mystery to all researchers of this phenomenon. This question is important for the problem of the origin of the Moon.
After the Earth's magnetic field and the possible field of the Sun were discarded, we turned to a possible lunar dipole field, which should have disappeared no earlier than 3.1 eons ago. One proposal, made by Runcorn in particular, envisaged the existence of an iron core smaller than that of the Earth, which would therefore have to rotate very quickly to create the required field. This seems unlikely, since seismic observations have not detected a core, although they may not be entirely conclusive. If such a spinning iron core was present early on, more than 3.1 eons ago, this would indicate that it had cooled and therefore the field might not be present today. In another case, it is assumed that the interior of the Moon accumulated at low temperatures and magnetizable particles, namely iron, accumulated in the primordial magnetic field of the Sun, which led to the formation of a permanent magnetic dipole field that persisted until radioactive heating led to an increase in temperature above Curie points. However, in this case, the surface areas must be molten to create highly differentiated areas with lava flowing to the surface.
The popular view is as follows. The Moon accumulated first from solids at low temperatures due to low gravitational energy and accumulation rate, and later at high gravitational energy and accumulation rate. This created a solid interior and a molten surface. It is estimated that accumulation must have occurred over a period of about 2000 years or less to form a molten surface, despite radiative losses. Consequently, such a bombardment should have ended quite abruptly. It is difficult to determine the location in the solar nebula where this could happen. An alternative is Urey's gas spheres (1972). In this case, solids are deposited in the inner part of the sphere when it is cold, but when the sphere is compressed, the temperature inside increases and thus the inner part is formed cold, and the surface accumulates at higher temperatures. The Moon cooled after the hot Sun moved away from the gaseous sphere, and, whatever the mode of accumulation of the Moon, the magnetic field carried out by the cold interior magnetized the cooled surface rocks and disappeared when, due to radioactive heating, the temperature of the cold interior exceeded the Curie point. As stated above, this is the most interesting problem that has amazed many people who have studied the Moon.
THEORIES OF THE ORIGIN OF THE MOON
To discuss theories of the origin of the Moon, it is necessary to consider the theory of the origin of the planets and their satellites, essentially the origin of the solar system. Jupiter and the system of its inner satellites are similar in orbital characteristics to the Sun and planets; Jupiter's rotation axis is approximately perpendicular to the ecliptic plane. If other planets and their satellites reproduced the same structure, then there would be no great disagreement in views on the origin. One could assume that the planets and their satellites accumulated from clusters of small gas and dust objects. However, Earth, Venus, Mars, and the major planets other than Jupiter have rotation axes that are not perpendicular to the ecliptic plane, requiring collisions of very massive bodies to form planets. This alone indicates the presence of massive bodies at the dawn of the history of the solar system.
If all the terrestrial planets had large satellites, like the Earth, it could be assumed that these planets and their satellites formed as double planets, that is, they accumulated from solid and liquid silicates in close proximity to each other. In this case, the question of the origin of satellites would not be subject to controversy and discussion, as has been the case for many decades. It is the uniqueness of the Moon, as the only very large satellite, that poses an interesting and controversial problem of its origin to scientists. After all, if the formation of double planets is the rule, the absence of a large Moon for Venus and the same satellites for Mercury and Mars becomes a new mystery. Soviet scientists, in particular O. Yu. Shmidt, V. S. Safronov and B. Yu. Levin, support a theory suggesting the accumulation of many small satellites that surrounded the Earth during its formation over a period of about 100 million years.
Cameron and Ringwood defend the view that the Earth and Moon accumulated in a short period of time from 10 3 to 10 4 years at very high temperatures and in the form of a double body. The Moon accumulated a volatile, high-temperature substance that formed a ring around the Earth. The mass of the Earth plus its corresponding share of solar gases must have amounted to a mass approximately equal to the mass of Jupiter, originally distributed in the disk surrounding the Sun. It is necessary that at some point 0.3% of the solid substance intended to form solids separates from the 99.7% mass of gas and accumulates in a limited volume. It can be assumed that this could only happen if the substance was at a low enough temperature to condense into a liquid or solid. It's possible that if particulate matter settled toward the midplane of the cloud, this could happen. The described model has something in common and is to some extent identical to the Kuiper theory of protoplanets, the weak point of which was the explanation for the loss of gas mass equal to the mass of Jupiter. Urey pointed out that this was impossible, and to date no satisfactory explanation has been offered for the loss of gases. It is possible (but not proven) that the magnetic fields of Solptz's rotating magsite dipole could enable the release of gas.
Ringwood, based on the fact that the loss of volatiles is so characteristic of the substance of the lunar surface, indicates that the Moon must have been released from high-temperature gases. This is a very strong argument, especially if the amount of these elements is reduced throughout the body of the Moon, which is still an unconfirmed assumption. The abundance of the most common elements in lunar rocks is so closely similar to what is theoretically expected during the fractionation of molten silicates that it seems possible to abandon the hypothesis of a large role for volatilization. Moreover, a mechanism is needed to ensure the tilt of the Earth's axis and a certain change in the lunar orbit, since Goldreich points out that the modern orbit of the Moon could not originally have been in the plane of the Earth's orbit. Both of these phenomena require the presence of other sufficiently large bodies, which, colliding with the Earth and the Moon, caused the mentioned changes. If this were true, then similar objects colliding with other planets would lead to similar effects. The fact that Venus has no satellite and rotates in the opposite direction is perhaps the most convincing evidence against the given theory of the origin of the Earth and the Moon. Marcus and V.S. Safronov emphasized that such collisions were necessary, and Urey gave an explanation for the formation of such objects. It has recently been suggested that large pre-planetary bodies existed and collided during the formation of the Earth in high temperature conditions, and according to the Ringwood model, the Moon "evaporated" from the Earth. Elements that volatilize at temperatures of 1500° K and below have disappeared from the lunar surface, but there is no reason to believe that there is a significant differentiation between silicon, on the one hand, and aluminum, magnesium, calcium, on the other, even if there are large differences in volatility . The author of this work doubts the correctness of Ringwood's hypothesis about the gas, silicon, aluminum, etc. atmosphere that gave birth to the Moon. Perhaps, if it were possible to extract rocks from deeper layers and they showed a low content of volatiles, this could serve as an indication that the substance of the Moon in a highly fragmented form was heated to a temperature of 1000-1500 ° C and that the volatiles were carried away by residual gases. Those who are inclined to think that titanium-iron basalts are, in essence, lava flows from the depths, perceive this statement as already proven. The author of this work would like to examine samples of rocks belonging to the so-called local lava flows, which may have been carried out from the deep layers, before accepting this point of view.
Sir George Darwin hypothesized that the Moon separated from the Earth, and this idea has been discussed many times during this century by both its supporters and its opponents. Wise and O'Keefe recently reviewed this debate. The density of the Moon's rocks is close to the density of the Earth's mantle rocks, and this mysterious question is easily solved by this hypothesis. Much effort has been expended to prove the possibility of such a separation. In recent years, this hypothesis has been partly, and perhaps completely, shaken by studies of the chemical composition of rocks on the lunar surface. Lunar basalts have definitely higher concentrations of iron and titanium and definitely lower concentrations of volatile elements compared to terrestrial ones. Of course, it cannot be completely ruled out that such differences could have arisen in the complex process of high-temperature separation, but this seems unlikely. The age of lunar rocks pushes back the time of separation by 4.5 eons. One circumstance is important, obvious from the old data. If the Earth and Venus were formed as a result of similar processes at comparable distances from the Sun, then why does the Earth-Moon system have a very large positive angular momentum relative to the orbital momentum, while Venus has a small and negative value for the same quantity? Why didn't Venus become a high-momentum planet and become a double planet? These questions could have been asked many years ago. At present, the hypothesis of the separation of the Moon from the Earth seems unlikely.
The capture hypothesis has been especially popular since Gerstenkorn investigated this problem. It was discussed by MacDonald, Alfven and others.
This hypothesis has the obvious advantage that it emphasizes the random nature of the origin of the Moon, and in this case there is no need to explain the lack of satellites of other terrestrial planets. However, it is necessary to assume that there were many moons at one time in the early development of the solar system if we are to avoid many improbable assumptions. The probability of the Moon being captured in some orbit around the Earth is less than the probability of being captured when it collides with the Earth. These issues were discussed in detail in the work of Urey and MacDonald. Gerstenkorn came to the conclusion that the capture occurred in an orbit with a backward motion, which then turned, passing over the Earth's belts, and the motion became direct. It was assumed that the minimum orbit was near the Roche limit at a distance of 2.9 Earth radii for a body with the density of the Moon. During the capture process, a large amount of energy must have been dissipated in the form of heat, namely on the order of 10 11 erg per gram of lunar material. Some of this energy should have been dissipated in the Moon, probably in the surface layers and could have caused the formation of its molten surface layer, as discussed above. Such a melting process would be more intense in the hemisphere of the Moon facing the Earth, and could lead to the appearance of larger areas of seas on the surface of this hemisphere. If such heating engulfed the entire body of the Moon, the existence of mascons would become very doubtful. Urey and MacDonald tend to think that collisions with other bodies orbiting the Earth contributed to the capture and that the initial orbits could have been much larger, thus eliminating heating difficulties. In addition, under this assumption, the angular momentum density of the initial accumulation of the Earth falls on the empirical curve of MacDonald, who showed that the logarithm of the angular momentum density of planets, graphically represented as a function of the logarithm of mass, has the form of a straight line with a slope of about 0.82.
This hypothetical model for the origin of the Moon postulates that the Moon accumulated somewhere else. If we accept the capture hypothesis, the problems of the mode of accumulation and the overall chemical composition remain open. Until now, only a model of the gas sphere has been proposed, but other models are possible, although their plausible calculation is difficult. In this case, it is believed that two-dimensional gravitational instabilities have arisen in the flat disk of the nebula according to the formula proposed by Jeans and refined by Chandrasekhar. When applied to this problem, the formulas should be considered approximate due to the fact that the presence of solid particles leads to an increase in instability.
The temperatures required for the formation of Moon-sized bodies in the nebula are very low, and the mass of the cloud must be a significant fraction of the mass of the Sun. As Alfvén suggests in his magnetic field-assisted hypothesis, mass of this order of magnitude must have been lost from the protosun to reduce its angular momentum, and Herbig believes that T Tauri stars must have dust clouds of approximately solar mass.
The accumulation of lunar masses in the center of such gas formations as a result of the influence of gravity with accumulation energy absorbed by a large mass of gas could occur at low temperatures if the radii were large. If the gas mass was subsequently compressed, the surface layers of the central lunar object could heat up to high temperatures, the reduced liquid iron would carry out siderophile elements, and liquid iron sulfide - chalcophile elements. With the slow disintegration of gas spheres there would be a slow cooling of the central mass, and with the complete disappearance of gases there would be a more rapid cooling to low temperatures. The chemical composition remains a difficult problem. In the case of low relative iron content in the Sun, as was believed for many years, the Moon consists of primary non-volatile solar matter, but with a revision of the relative concentrations of elements in solar matter, the density of primary non-volatile solar matter becomes close to 4 g/cm 3 and does not correspond to density of the Moon. If the capture hypothesis is to be taken seriously, this problem must be solved. Carbonaceous chondrites are a very common type of meteorite based on impact observations, and among them, type III (Vigarano group) has the appropriate density and low potassium content, so that a solid Moon can be created if the central body had this or similar chemical composition. These meteorites contain water and large amounts of carbon. The low water and carbon content in surface samples sharply contradicts this assumption, but does not exclude it. Marcus V. S. Safronov and Hartman considered other ways of accumulating large bodies from smaller solids in the absence of gas, which is certainly necessary if the more volatile elements are removed from the interior of the Moon. In this case, the sequence of events should have led to the loss of volatiles at a temperature of the order of 1500° K and they should have disappeared from the region in which the Moon and Earth accumulated before accumulation began. If volatiles are contained in the interior of the Moon, this indicates the formation of the Moon in the gaseous sphere, and the Earth must have been formed from the debris of such objects. Cameron recently proposed that the Moon condensed from a gaseous solar nebula within the orbit of Mercury, where the least volatile constituents, namely CaO and Al 2 0 3, condensed. They formed the Moon, which was thrown by Mercury into an orbit intersecting the orbits of Venus and Earth, and then captured by the Earth. Thus, the Moon formed in the region of the solar nebula, where iron remained largely in gaseous form. This explains the low density of the Moon and, possibly, its chemical composition. Both of these mechanical events seem incredible, although they cannot be completely rejected. If the Moon were captured, it would have formed independently of the Earth as a separate primordial planet, and in that case would likely have been older than the Earth. Currently known age indicators indicate that the Moon as an independent body existed around the era of meteorite formation. The possibility of establishing the age of the Earth using the same method has been lost.
As stated above, Jupiter and its moons resemble a “small” solar system, and one gets the impression that these satellites formed in the immediate vicinity of the planet. The fact that there are seven satellites in the solar system equal in size to Earth's Moon, and that the average mass of other satellites and asteroids is approximately one-quarter the mass of Earth's Moon, indicates that lunar-sized objects are favored in the solar system. Axial tilts The rotations of the planets give reason to think that there were large objects nearby that collided with the forming planets in the last stages of their accumulation. It is possible that our Moon is not such a unique body as is often thought!
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In this chapter we will look at how the Moon acts with its gravitational field on the Earth itself, i.e. on her body and her orbital movement. The consequences of this impact for various terrestrial spheres - lithosphere, hydrosphere, core, atmosphere, magnetosphere, etc., as well as for the biosphere, will be discussed in the following chapters.
ATTENTION!
See graphs of the gravitational interaction of the Moon and Earth using the service
LUNAR FACTOR
Calculation ratios and constants
To calculate the gravitational influence of the Moon, we will use the formula of classical physics, which determines the force F of the mutual attraction of two bodies with masses M1 and M2, the centers of mass of which are located at a distance R from each other:
(1) F (n) = (G x M1 x M2) / R 2,
where G = 6.67384 x 10 -11 is the gravitational constant.
This formula gives the value of the force of attraction in SI units - newtons (n). For the purposes of our treatise, it will be more convenient and clearer to operate with kilograms of force (kgf), which are obtained by dividing F by a factor of 9.81, i.e.:
(2) F (kgf) = (G x M1 x M2) / (9.81 x R 2)
For further calculations we will need the following constants:
- Moon mass - 7.35 x 10 22 kg;
- the average distance from the Earth to the Moon is 384,400 km;
- the average radius of the Earth is 6371 km;
- mass of the Sun - 1.99 x 10 30 kg;
- the average distance from the Earth to the Sun is 149.6 million km;
The force of lunar gravity on Earth
In accordance with formula (2), the force of attraction by the Moon on a body weighing 1 kg located in the center of the Earth, with a distance between the Moon and the Earth equal to its average value, is equal to:
(3) F = (6.67 x 10 -11 x 7.35 x 10 22 x 1) / (9.81 x 384400000 2) = 0.000003382 kgf
those. just 3.382 micrograms. For comparison, let’s calculate the force of attraction of the same body by the Sun (also for an average distance):
(4) F = (6.67 x 10 -11 x 1.99 x 10 30 x 1) / (9.81 x 149600000000 2) = 0.000604570 kgf,
those. 604.570 micrograms, which is almost 200 (two hundred!) times greater than the gravitational force of the Moon.
In addition, the weight of a body located on the surface of the Earth varies within much more significant limits due to the deviation of the Earth’s shape from the ideal, uneven relief and density, as well as the influence of centrifugal forces. For example, the weight of a body weighing 1 kg at the poles is approximately 5.3 grams greater than the weight at the equator, one-third of this difference is due to the oblateness of the Earth at the poles, and two-thirds is due to the centrifugal force at the equator, directed against gravity.
As you can see, the direct gravitational effect of the Moon on a specific body located on Earth is literally microscopic and at the same time significantly inferior to the gravitational effect of the Sun and geophysical anomalies.
Lunar Gravity Gradient
Let's turn to Fig. 3.1. For the average value of the Earth-Moon distance, the force of attraction by the Moon on a body weighing 1 kg located on the surface of the Earth at the point closest to the Moon is 3.495 micrograms, which is 0.113 micrograms more than the force of attraction of the same body, but located in the center of the Earth. The force of attraction of a body located on the surface of the Earth by the Sun (also for the average distance) will be 604.622 micrograms, which is 0.052 micrograms greater than the force of attraction of the same body, but located in the center of the Earth.
Fig.3.1 Lunar and solar gravity
Thus, despite the immeasurably smaller mass of the Moon compared to the Sun, the gradient of its gravitational force in the Earth’s orbit is on average more than two times greater than the gradient of the gravitational force of the Sun.
To illustrate the effect of the Moon's gravitational field on the Earth's body, let us turn to Fig. 3.2.
Fig. 3.2 The influence of the gravitational field of the Moon on the body of the Earth.
This figure presents a very, very simplified picture of the reaction of the Earth’s body to the influence of lunar gravity, but it reliably reflects the essence of the process - a change in the shape of the globe under the influence of the so-called. tidal (or tide-forming) forces directed along the Earth-Moon axis, and the elastic forces of the Earth's body counteracting them. Tidal forces occur because points on the Earth closer to the Moon are attracted to it more strongly than points further away from it. In other words, the deformation of the Earth’s body is a consequence of the gradient of the gravitational force of the Moon and the elastic forces of the Earth’s body counteracting it. As a result of the action of these forces, the size of the Earth increases in the direction of action of tidal forces and decreases in the transverse direction, as a result of which a wave called a tidal wave is formed on the surface. This wave has two maxima, located on the Earth-Moon axis and moving along the Earth's surface in the direction opposite to the direction of its rotation. The amplitude of the wave depends on the latitude of the area and the current parameters of the Moon’s orbit and can reach several tens of centimeters. It will have its maximum value at the equator when the Moon passes its perigee.
The Sun also causes a tidal wave in the Earth's body, but significantly smaller due to the smaller gradient of its gravitational force. The joint gravitational influence of the Moon and the Sun on the Earth's body depends on their relative position. The maximum value of tidal forces and, accordingly, the maximum amplitude of the tidal wave is achieved when all three objects are located on the same axis, i.e. in a state of so-called syzygy(alignment), which occurs during a new moon (Moon and Sun in “conjunction”) or during a full moon (Moon and Sun in “opposition”). The configuration data is illustrated in Fig. 3.3 and 3.4.
Fig. 3.3 The combined influence of the gravitational fields of the Moon and the Sun on the body of the Earth
in “conjunction” (on the new moon).
Fig. 3.4 The combined influence of the gravitational fields of the Moon and the Sun on the body of the Earth
in “opposition” (during the full moon).
As the Moon and Sun deviate from the syzygy line, the tidal forces they cause and, accordingly, tidal waves begin to acquire an independent character, their sum decreases, and the degree of their opposition to each other increases. The opposition reaches its maximum when the angle between the directions to the Moon and the Sun from the center of the Earth is 90°, i.e. These bodies are in a “square”, and the Moon, accordingly, is in a quarter phase (first or last). In this configuration, the tidal forces of the Moon and the Sun act strictly oppositely on the shape of the Earth’s body, the corresponding tidal waves on the surface are maximally separated, and their amplitude is minimal, as illustrated in Fig. 3.5.
Fig. 3.5 The combined influence of the gravitational fields of the Moon and the Sun on the Earth’s body in a “square”.
The physics of the Earth's tidal processes under the influence of the gravitational fields of the Moon and the Sun is very complex and requires taking into account a large number of parameters. A large number of different theories have been developed on this topic, many experimental studies have been conducted, and a huge number of articles, monographs and dissertations have been written. Even today, there are many “blank” spots, conflicting points of view and alternative approaches in this area. For those wishing to delve deeper into the problems of earth's tides, we can recommend the fundamental study of P. Melchior “Earth's tides” (translated from English, M., “Mir”, 1968, 483 pages).
The effect of lunar gravity on Earth results in two fundamental phenomena:
- Lunar tides on the Earth's surface are periodic changes in the level of the Earth's surface, synchronized with the daily rotation of the Earth and the movement of the Moon in orbit.
- The imposition of a variable component on the Earth's orbit, synchronized with the rotation of the Earth - Moon system around a common center of mass.
These phenomena are the main mechanisms of the Moon’s influence on the earth’s spheres - the lithosphere, hydrosphere, earth’s core, atmosphere, magnetosphere, etc. More about this in the next chapter.
Earthquakes are a frequent phenomenon, which is also one of the most inexplicable and mysterious natural disasters. Scientists cannot always say with certainty what exactly is causing them, not to mention timely forecasts and preventive measures.
Moon's gravitational field
We are well aware that the gravitational attraction of the Moon, together with the gravitational field of the Sun and the inertia from the rotation of the Earth, affects the formation of tides. In other regions of the Solar System, the gravitational relationship of planets and satellites causes strong tectonic phenomena.
Seismologists have long wondered about the possible influence of our own satellite's underestimated gravitational field. Of course, the Moon's tidal locking is not strong enough to turn rocks on Earth into hot lava, but it may be enough to influence weak points in tectonic plate junctions.
Tectonic faults
In the earth's crust, there are subduction zones - places where one part of the tectonic plate plunges into the mantle and goes under another part of the earth's crust. These subduction zones are a kind of “weak spots” of tectonic activity, and it is near them that strong earthquakes most often occur.
Based on these data, a group of scientists from the University of Tokyo proposed the following hypothesis: since subduction zones are most often deep faults, perhaps the gravitational force of the Moon is enough to influence the divergence of tectonic plates. Even though tidal locking on the Moon may not be enough to initiate movement of the entire plate, it can cause small cracks, which in turn create a snowball effect and lead to strong shaking.
Lunar cycles
To confirm the hypothesis, Japanese scientists examined seismic readings of the last twenty years and compared them with syzygies - the alignment of the Moon, Earth and Sun in a straight line. If the longitude of the Moon coincides with the longitude of the Sun, a new moon is observed on earth, and the gravitational fields of the Moon and the Sun combine and “pull” one of the Earth’s hemispheres towards itself. In the case when the longitude of the Moon is opposite to the longitude of the Sun, we observe a full moon, and the gravitational field of the satellite “pulls” one hemisphere of the Earth towards itself, and the gravitational field of the Sun attracts the other. In both cases, the influence of external gravity on the earth's surface reaches its maximum and can cause tectonic movement.
By comparing data on earthquakes with syzygies, scientists obtained interesting data. During full moons, devastating earthquakes occurred in the Indian Ocean in 2004, as well as one of the most powerful earthquakes recorded in history - in February 2010 in Chile.
During the new moon, the combined gravitational field of the Moon and the Sun could explain the causes of the Great East Japan Earthquake, which had a devastating effect on the Tohoku region in March 2011.
conclusions
This study is not enough to conclusively prove the relationship between syzygies and earthquakes. However, indirect evidence paints a completely convincing picture of how, along with the ebb and flow of the tides, the Moon can from time to time attract not only water, but also the earth’s surface.
In recent decades, the question of the possible influence of the Moon and the Sun on the tectonic processes occurring on Earth and triggering the mechanisms for the formation of earthquakes has increasingly arisen. For example, the famous San Andreas fault became the site of the formation of about 80 thousand small tremors, tied to lunar syzygies.
Lunar mascons. A detailed study of the gravity field of the Moon became possible after the launch of space satellites into orbit of artificial satellites of the Moon. Observations of the satellite orbits were carried out using three ground stations.
By changing the frequency of the satellite transmitter, the so-called “radial accelerations” were determined - projections of the acceleration of gravity on the Earth-satellite direction (for the central part of the visible side of the Moon, these accelerations corresponded to the vertical component).
The first constructions of the picture of the gravitational field of the Moon were carried out by Soviet researchers based on the results of the flight of the Luna-10 spacecraft; the data were later refined by observations of the orbits of artificial satellites of the Lunar Orbitar series, as well as on those sections of the Apollo spacecraft routes where their orbits around the Moon were determined only by its gravity field.
The gravitational field of the Moon turned out to be more complex and heterogeneous than the Earth's, the surface of equal gravity potential is more uneven, and the sources of anomalies are located closer to the surface of the Moon. An essential feature of the lunar gravity field were large positive anomalies confined to circular seas, which were called mascons (from English - “mass concentration”). When approaching the mascon, the satellite's speed increases; After the flight, the satellite slows down slightly, and the orbital altitude changes by 60 - 100 m.
At first, mascons were discovered in the seas of the visible side: Rain, Clarity, Crises, Nectar, Humidity; their sizes reached 50–200 km (they fit within the contours of the seas), and the magnitude of the anomalies was 100–200 mgal. The Mare Mons anomaly corresponded to an excess mass of the order of (1.5–4.5) x 10 -5 the mass of the entire Moon.
Subsequently, more massive mascons were discovered at the border of the visible and far sides in the Eastern and Marginal Seas, as well as a huge mascon in the equatorial zone of the center of the far side of the Moon. There is no sea in this place, so the mask called it “Hidden”. Its diameter is more than 1000 km, its mass is 5 times greater than the excess mass of the Sea of Rains. The hidden mascon is capable of deflecting a satellite flying at an altitude of 100 km by 1 km. Total excess mass corresponding to positive gravity anomalies. exceeds 10 -4 lunar masses. A number of negative anomalies turned out to be associated with the lunar mountains: Jura, Caucasus, Taurus, Altai.
Gravity anomalies reflect the peculiarities of the distribution of masses of matter in the interior of the Moon. If, for example, we assume that mascons are created by point masses, then their depths should be about 200 km in the Sea of Rain, in the Sea of Clarity - 280 km, in the Sea of Crisis - 160 km, in the Sea of Tranquility - 180 km, in the Sea of Abundance - 100 km, in the Sea of Poznan - 80 km, Ocean of Storms - 60 km. Thus, gravity measurements revealed a heterogeneous density distribution in the upper mantle.
Electrical conductivity. None of the lunar expeditions made direct measurements of the Moon's electric field. It was calculated from variations in the magnetic field recorded by magnetometers at the Apollo 12, -15, -16 and Lunokhod 2 stations.
The Moon, deprived of a magnetosphere, during its rotation around the Earth periodically finds itself in the undisturbed Earth's magnetosphere on a full moon, in the solar wind on a new moon, and twice for 2 days in a transitional one. shock layer.
Fluctuations of the external interplanetary magnetic field penetrate into the Moon and induce an eddy current field in it. The rise time of the induced field depends on the distribution of electrical conductivity in the lunar interior. Simultaneous measurements of the external alternating field above the Moon and the secondary field on the surface make it possible to calculate the lunar electrical conductivity.
The Moon is designed “conveniently” for magnetic-telluric sounding. The interplanetary magnetic field extended from the Sun is uniform, its front can be considered flat, and therefore for research it does not require a network of laboratories, as on Earth. Due to the fact that the Moon has a higher electrical resistance than the Earth, two hourly observations are sufficient to sound it, whereas on Earth it takes annual observations.
The solar wind, which has high conductivity, flows around the Moon, as if wrapping the Moon in foil, without releasing the fields induced in the depths to the surface. Therefore, on the sunny side of the Moon, only the horizontal component of the alternating magnetic field can be used, while on the night side, where the vertical component also works, the situation is more similar to that on Earth.
The Apollo magnetometers recorded the Moon's reaction in the solar wind on the night and day sides, as well as in the geomagnetic plume, where the plasma effects of the solar wind are minimized.
In the Lemonier crater on the sunny side of the Moon, Lunokhod 2 recorded the formation of fluctuations in the solar magnetic field over time. In this case, the horizontal component of the magnetic field reflects the deep electrical conductivity of the Moon, and the value of the vertical component over a long period of time characterized the strength of the external field of the Moon. The experimental apparent resistivity plot was interpreted by comparison with the theoretical curves.
Soviet (L.L. Vanyan and others) and foreign (K. Sonet, P. Dayel and others) researchers have constructed various models of the electrical conductivity of the Moon. Differing in some details, they give generally similar distributions of the electrical properties of lunar material with depth: in the upper 200 km away there is a poorly conductive layer with a resistivity of more than 106 ohm m; deeper lies a layer of low resistance (103 ohm m) with a thickness of 150–200 km; up to 600 km, the resistance increases by an order of magnitude and then decreases again to 103 ohm m at a depth of 800 km (Fig. 9).
Rice. 9. Deep structure of the Earth (thick lines) and the Moon (thin) according to geophysical data:
1 - longitudinal wave velocities; 2 - shear wave velocities; 3 - electrical conductivity. Vertical scale - depths in relation to the corresponding radii of the Earth and Moon
Electrical soundings of the Moon carried out to date reveal the following main features:
The Moon in general has a higher resistance than the Earth. On top of it there is a powerful insulating layer; electrical conductivity increases with depth. Radial stratification of the Moon has been discovered and inhomogeneity in the horizontal direction in electrical resistance is noted.
Based on the profiles of electrical conductivity and the dependence of conductivity on temperature, the temperature inside the Moon was estimated for different mantle compositions. In all cases, down to a depth of 600–700 km, the temperature lies below the melting point of basalts, and at greater depths it reaches or exceeds it.
Comparing deep temperatures with the melting temperatures of rocks at different pressures allowed scientists to estimate such an important physical parameter as the viscosity coefficient. It characterizes the ability of rocks to move under stress.
The upper 200 - 300 km shell of the Moon has a very high viscosity coefficient of 10 26 - 10 27 poise. This is 2–3 orders of magnitude higher than at the corresponding depths of the Earth, even if we take the hardest regions of ancient crystalline shields. From the surface to the center of the Moon, the viscosity decreases; deeper than 500 km it decreases by 100 - 1000 times, i.e. it becomes comparable with the viscosity of the Earth's mantle. In the asthenosphere of the Moon, the viscosity sharply decreases to values characteristic of the asthenosphere of the Earth (10 20 - 10 21 poise).
Heat flow. Before spacecraft flights, it was believed that the content of radioactive elements 235 U, 238 U, 232 Th, 40 K in the interior of the Moon was on average the same as in chondritic meteorites or in the Earth’s mantle. The heat flow coming from the depths of the Moon through its surface was estimated by analogy with the corresponding flow of the Earth, where every second every 1 cm 2 of the surface “evaporates” into space 1.5 - 10 -6 cal of heat. The radius of the Moon is 3.6 times smaller than that of the Earth, its surface is 7.5%, and its volume is 2% of the Earth's. Provided that the concentration of radioactive isotopes per unit volume was the same, the heat flux value for the Moon was predicted to be 0.36 × 10 -6 cal/cm 2 s.
In 1964, Soviet astronomers led by V.S. Troitsky measured the thermal radiation of the Moon in the wavelength range from 1 mm to 3 cm and obtained an unexpectedly high average heat flux (0.85 - 0.95) 10 -6 kcal/ cm2s, almost three times higher than calculated. This could indicate a higher content of radioactive isotopes or that heat sources are concentrated near the surface.
The unexpected result was confirmed by direct measurements of heat flow on the Moon. Direct measurements of heat flow on the lunar surface were carried out during two astronaut expeditions to the Moon: in July 1971 in the Hadley Rill region on the eastern edge of the Mare Mons (Apollo 15) and in December 1972 in the Taurus-Littrov region in the narrow gulf in the southeast of the Sea of Clarity (“Apollo 17”). The astronauts drilled holes, inserted fiberglass tubes and placed thermal probes in them to measure temperature and thermal conductivity. Each probe provided measurements at 11 depths and consisted of 8 platinum resistance thermometers and 4 thermocouples. Two probes were installed at depths of 1 and 1.4 m at the Apollo 15 station and one at 2.3 m at Apollo 17. Readings were transmitted to Earth every 7 minutes. Data for 3.5 years for the first and 2 years for the second stations were processed. The signals began to be analyzed only a month after the launch of the instruments, when their thermal equilibrium with the regolith was established. Despite the huge thermal contrasts on the surface (+130 °C during the day, - 170 °C at night), temperature fluctuations practically died out at a depth of 0.8 m, while annual temperature fluctuations were felt at all depths studied. To measure the thermal conductivity of the lunar soil, electric heaters were turned on for 36 hours upon command from the Earth. As the temperature increased, the thermal conductivity value was determined. The thermal conductivity of the regolith turned out to be very low and strongly dependent on temperature. At the surface it was only 0.3 10 -5 kcal (cm K) -1, deeper as compaction it increased, reaching values of ~0.24 10 -4 kcal (cm) at a depth of 1–2 m K) -1, in the 250-meter upper layer, thermal conductivity apparently remains very low, 2–3 orders of magnitude less than in the interior of the Moon, 10 times less than in the excellent heat insulator - air, and 40 times less than in water. Thus, the regolith of the Moon, formed as a result of the grinding of clastic rocks by meteorite impacts, represents a kind of “blanket” that plays the role of a thermostat for the Moon and reduces the loss of its heat. For example, during the formation of the Sea of Mons, vast surrounding areas were covered with clastic rocks. Due to this, over the past 100 million years, the temperature at a depth of 25 km should have risen from 300 to 480 °C. Based on the thermal conductivity and temperature difference, the heat flow passing through the surface of the Moon was calculated. Its values for the Apennine region are 0.53 10 -6 kcal (cm 2 s) -1, in the Descartes region - 0.38 10 -6 kcal (cm 2 s) -1. The difference is 40% greater than measurement errors, the effect of local relief, and characterizes the horizontal variability of the content of radioactive isotopes in the lunar crust.
