In this chapter we will focus on summaries about the geology, topography and other features of our cosmic neighbor
Earth's Moon - Summary of Findings Part 1
Age and origin of the moon
Based on the data of the Prospector Lunar spacecraft, it was estimated that the moon was formed 4.5 billion years ago. A huge rock block whose mass is equal to 3 masses of Mars hit the Earth. Large amounts of dust and many fragments of rocks created by the collision flew a great distance and entered the orbit around the earth in the formation of a very thick cloud. Little by little they began to stick together until a very large lump was formed. In the course of one year most of the matter crystallized into one unit - the moon (22). Different explanations raise the possibility that the heat generated during this collision as well as the material compressed to form the moon, created a sea of trend that existed for millions of years. Minerals rich in iron that moved through the trend formed the mantle of the moon and in contrast minerals with little iron, these minerals plagioclase (Plagioclasses) crystallized and floated on the surface. According to another model, the formation of the moon was done with less energy and the surface crystallized quickly. In such a case the plagioclase reached the surface in a series of volcanic activities. The large and extensive explosiveness of the plagioclase raises the possibility of a process on a global scale (23).
Following the differentiation between the crust and the mantle, a wave of volcanic activity came 3-4 billion years ago when basaltic lava erupted to the surface and filled the floor of many craters and other low places and created the mares, the name given to these areas by researchers The first moon that used telescopes. They thought they were seeing oceans. These are actually huge plains. One of the unclear phenomena is the uneven explosiveness of these basalt plains. Close to a third of the visible side is covered by basalt planes and their extent on the hidden side is smaller. The thickness of the crust on the hidden side is greater than on the visible side. Moreover, most lunar volcanism is more basaltic than silicic. Rich in minerals containing more iron and magnesium than silica and aluminum (24).
Examining the prevalence of lunar craters compared to those found on Earth can raise a completely different possibility as to the origin of the moon. There are tens of thousands of craters on the moon, on the other hand, their number on Earth is only a few hundreds - 200. This can be explained by weathering processes that eroded the earth's craters and the filling of their floor with dust carried by winds for hundreds of millions of years raised their surface up to the edge of the craters. Among the lunar craters there are those with a diameter of hundreds of kilometers and in some cases their diameter exceeds 1000 kilometers such as the Imbrium basin. There are no craters of this size on Earth. Weathering cannot consume them all. Due to their dimensions, different parts of them would always remain throughout geological periods up to the present day. While comparing with the inner planets Mercury, Venus and Mars, the possibility that the moon was formed elsewhere in the solar system must be taken into account. It circled it in its own orbit, or was a moon of one of the gaseous planets. For an unknown reason it broke off from its orbit and moved towards the sun and while it was moving it was captured by the Earth's gravity and entered orbit around it (25).
topography
Since they started photographing the moon using spacecraft, it became clear that there is a noticeable difference between the visible side and the hidden side. The visible side is low and relatively flat and the hidden side is high, mountainous and the crust is thicker. According to one explanation, the formation of the plateaus involves heat generated by crustal tides 4.5 billion years ago, shortly after the formation of the Moon. The crust is separated from the mantle by an ocean of magma. As a result, the Earth's gravity caused the crust to bend and heat up. At the poles, where the bending and heating were greatest, the crust became thinner, while the thick crust formed in the areas in a straight line with the Earth. It should be borne in mind that this process does not explain why the levels of the moon are found only on the hidden side. Both sides of the moon had to have plateaus since the tides have a symmetrical effect. It could be that during 4.5 billion volcanic activity or other geological processes changed levels that were on the visible side. The crustal thickness mapping based on gravitational information indicates that the crust below the levels of the hidden side is thick. The changes in the thickness of the crust are similar to the effects discovered in Europa, Jupiter's moon covered by an ice shell over an ocean of liquid water, although there is a fundamental difference between these two moons (26).
underground spaces
An interesting phenomenon found on the moon is underground cavities. This phenomenon was first observed at Marius Hills. Holes were found in the ground that could lead to an underground tunnel. This discovery strengthens the evidence for the existence of underground channels carved by lava. It seems that there are lava tubes on the moon that resemble similar structures on Earth. These channels are formed when the upper part of a flow of molten rock solidifies, the lava inside solidifies and an empty tube configuration remains. What sparked this line of thought are long sinuous sinus rilles carved into the surface by lava flows. Some of the rilles have collapsed and they raise the possibility of the invention of lava tubes under the surface. The opening in Marius Hills is 65 meters long. Based on illuminations at different angles of sunlight, they came to the conclusion that it is 80 meters deep and that the width of the lava tube is 370 meters (27). The Indian lunar probe Chandrayaan 1 also found an underground cavity, albeit of a different shape. According to the Indians it is a large underground chamber near the equator in Oceanus Procellarum. It is 1.6 km long and 120 meters wide (28).
Craters and basins
The most striking phenomenon on the moon is all the craters that cover large parts of the surface. Their investigation is done according to a number of indicators - their geographical distribution, diameter/depth ratio, size, bottom and inner and outer walls. On the surface of the moon there are tens of thousands of craters and their diameter ranges from a few meters, as observed by the Apollo pilots who stayed on its bottom, to very large craters that are hundreds of kilometers in diameter and more. Among them are some that are larger than 1000 kilometers in diameter. There are some whose floor is smooth as a result of a lava flow that leveled the surface, and there are some whose center has a bump. The bump is the product of a shock wave that penetrated deep into the ground following the same meteorite or asteroid that hit the ground and created these craters. The penetration of the shock wave can reach tens of kilometers underground. This wave returned to the surface of the ground and in the process lifted up the center of the crater floor. There was actually a lifting of part of the crust and/or mantle. The reliefs created can be very high and compared to them there are craters whose reliefs are on the order of cliffs. Already in a first comparative observation one can see that there is a fundamental difference between the visible side and the hidden side. The number of craters with a diameter of hundreds of kilometers or more is greater on the visible side than on the hidden side. Since the number of craters on the moon is very large, findings of a very limited number of craters will be mentioned here, mainly those for which the information is up-to-date since the launch of the Clementine spacecraft on January 25.1.1994, XNUMX.
The Mendel-Rybery basin is actually known 50 years since it was discovered -1962, but it was impossible to distinguish different details in it. The resolution of the photographs was too small to carry out topographical studies and deep geological studies. The photographs taken by the Clementine changed the picture completely. It turned out that the diameter of the basin is 600 kilometers and its depth is 5 kilometers, a depth similar to that of the neighboring Orientale basin (the diameter of this basin is 930 kilometers and its depth is 7 kilometers). Another basin, Coulomb Sorton was familiar, but the new data clarified the picture. It is a basin with a diameter of 500 kilometers and a depth of 6 kilometers, similar to relatively new craters. A crater that was discovered for the first time is the Cruger crater located east of the Lagan Orientale crater. It is located near a large outlet. The diameter of the crater is 400 kilometers and its depth is 3-4 kilometers. The crater itself is partially flooded by lava that probably came from the floor of an older basin that was there. To the east of Mare Frigoris there is a circular depression with a diameter of 500 kilometers and a depth of 2 kilometers. There are low plains and high plains and it is surrounded by an extensive and semi-circular area of craters, which probably indicates an old basin that was obliterated (1).
Researchers from Ohio University have found remains of a crater that impacted and created the formation known as "Man on the Moon". It appears that an asteroid-sized body hit the moon's hidden side and sent a shock wave through its core until it reached the visible side. This event is estimated to have occurred a billion years ago when the Moon was geologically active, a time when the core and mantle were still molten and there was a flow of lava (29).
Aristarchus Crater was photographed with unprecedented resolution, 40 cm per pixel. Its diameter is 40 kilometers and its depth is 3.5 kilometers. It was formed as a result of an asteroid impact 450 million years ago. The impact penetrated deep into the crust and produced dark lumps and ash of pyroclastic flows similar to the ash found in the Hawaiian Islands. Photographs in visible and ultraviolet light testify to the discovery of the mineral ilmenite, a titanium mineral rich in oxygen (30). The sides of the crater are actually blocks of rock from the lunar crust, before the impact of the asteroid that created it. You can distinguish light and dark materials on the sides. Dark streaks of molten impact material and rock fragments cover some of these materials, pyroclastic beads (volcanic glass formed during eruptions of fire pools similar to those found in Hawaii) found around the crater actually slid down the sides in dark streaks. This crater is one of the strongest reflectors of light on the moon due to the rocks carved deep into the crust. Next to the rocks that reflect light, there are those with low reflectance, which indicates a difference in their chemical composition. The northwestern part of the crater is made mainly of basalt and ash, while the south-southeastern part is made mainly of crustal rocks (anorthite and/or granite (31).
One of the most important discoveries was made by the Clementine spacecraft in relation to the Aitken Basin in the South Pole. Although this basin has been known for a long time, extensive and large-scale mapping of some of the large mountains near the South Pole raised the following hypothesis: since the lunar mountains are usually associated with basins, it is likely that a particularly large basin is located on the hidden side of the moon. In 1968, the Russian spacecraft Zond 6 transmitted 2000D stereo images to Israel and discovered a depression on the hidden side of the moon. This geological mapping identified huge mountains on the hidden side and patches of lava flows on high plateaus (mare lava) in the center of the South Pole. These findings raised the possibility that there is an ancient crater with a diameter of 2500 kilometers. In a survey made by the Clementine spacecraft, more precise measurements of the place were made And it turned out that the diameter of this crater is actually 2500 kilometers (for comparison, the diameter of the Hellas crater on Mars is 13 kilometers), the lowest point where it is 15 kilometers. Apollo XNUMX recognized that in the mountains inside the crater, there are large amounts of iron and thorium. The Galileo spacecraft that was on its way to Jupiter found that the ground inside the basin is darker than other levels on the moon. The Clementine spacecraft found that the floor of the basin contains large amounts of iron and titanium. Geologically, the hidden side can be divided into two types, the Aitken basin and the rest.
The dimensions of the pelvis can provide information about the way it was formed. The thickness of the crust on the hidden side is 70 kilometers on average, so the asteroid that hit the ground and created this crater, probably exposed the crust to its full length and threw a lot of material from it over the entire surface of the moon. Rocks from the mantle itself may also have been exposed. The possibility that the Aitken Basin is not the only large basin on the Moon has also been raised. The geochemist Peter Cadogen raised the possibility that on the visible side there is a larger impact basin with a diameter of 3000 kilometers which was given the name Gargantuan. Astronomer Ewen Whitaker mapped hundreds of formations on the visible side of the moon and identified an impact basin with a diameter of 3200 kilometers which was named the Oceanus Procellarum basin. The rim of the crater touches the western side of Oceanus Prcellarum, Gassendi, Sacrobosco, Pitatus. The eastern side of Tranquillitetes, Mare Macrobius, Atlas and at the northern end of Mare Frigoris. A careful examination of the Procellarum basin shows that in this place and at the western end there is a regional depression and that the demarcation line of the Procellarum basin is circular. The basin itself is not sufficiently developed on its eastern and western sides. The levels at its center are higher than its language. In impact craters their interior is lower than their lips. This body of data indicates that this place is basically a depression and that it was not created by a meteorite impact. This basin is actually a merging of several small basins, a concentric pattern related to the Imbrium basin or several other combinations. Its origin is probably in the interior of the moon since the early moon was extremely hot. Hot bodies can form depressions following the movement of liquid rock (1).
In new measurements of soil samples brought by the Apollo pilots, it is possible to notice signs of melting that existed before 3.9. billion years, which raises the possibility that the moon was bombarded by meteorites. The narrow range of the date of the bombardments raises the hypothesis that much of the meteorite activity lasted for 100 million years, probably due to collisions in the asteroid belt with comets that came from outside the solar system (32). A number of researchers compared observations of material blown from craters onto the surface of terrestrial planets (terrestrial bodies) and it turned out that there is more than one layer in them. It is possible that after the amount of material that was blown out following the impact that created the craters, there came a second phase of flying material during the last stages of creating the craters. This phase is a product of material that was melted by the impact itself, melting that occurred deep below the surface (33).
Mare Crisium is a basin formed by a meteorite impact on the moon. Its diameter is 500 kilometers and it is made of concentric rings. The inner ring is made of a dark material, touching the brightness levels. Arched peaks of the massifs are also found in them, except for an interval that extends along the eastern side of the basin. The diameter of the concentric ring is 492 kilometers and it contains irregular massifs that can be clearly distinguished on the western side of the Crisium basin, starting from the Cleomedes crater up to Tisserend Produs. This ring is separated from the inner ring by low recesses, in some of which, the floor is filled with mare-derived material (34).
conclusions
Mass concentrations or mass concentrators as we have seen have been known for several decades and are found in the following places:
Mare Serenitatais, Mare Crisium, Mare Humorum, Mare Nectaris, Mare Orientale,
The Prospector Lunar spacecraft apparently discovered 3 mascones on the visible side near the basins: Humboltianum,
Mendel-Rryberg, Schiller-Zuctius partial identification of 4 additional basins on the hidden side and they are:
Coulomb-Sarton, Hertrsrang, Freundia-Sharronov, Mare Moscvience
In the center of these basins the gravitation is at its peak compared to their surroundings inside the basins. As for the mascons that were known before the observations of the Lunar Prospecor, it is known that their floor is several kilometers thick. According to one of the explanations, the impact of large meteorites or asteroids penetrated deep into the crust and created a strong thermal anomaly and great pressures inside the crust. The heating of the crust and the weakening of the basin allowed the uplift of denser material from the mantle, which allowed for the concentration of more material in the center of the basin and the formation of a plug of material at this point in time. The basins were close to a state of isostatic balance. A topographic depression still remains. Another part of the depression is filled with basalt flows. This filling left the mascones in an unbalanced state buried in the basins and therefore the gravimetric anomalies of the mascones are of dense material from the mantle and material that filled them (35).
Volcanic activity
The first photographic evidence of volcanic activity, even if it had previously come from spacecraft orbiting the moon, is from the Taurus Litrow area photographed by Apollo 17. A comparative examination showed that volcanic rocks there are similar to those blown out of the terrestrial volcanoes Stromboli and Athena. Two researchers Head and McGetchio used photographs of volcanic eruptions in the terrestrial volcanoes using the slow motion technique and while introducing aerodynamic considerations and the influence of the moon's gravity showed that the deposits of the terrestrial volcanoes could also be in the Taurus Litrow region (36).
Confirmation for the assessment that there was volcanic activity on the moon in the past is found in the light and dark spots on the moon that can be seen even with the naked eye, which actually indicates the size of these spots. For years, astronomers have estimated that the origin of the spots found in the dark maria areas and the bright levels, is from volcanic activity in different geological periods. The reality of dome formations raises the possibility that there were overlaps between these geological periods. Astronomical observations and soil samples brought back by the Apollo pilots showed that the lava flows started 4 billion years ago and stopped 2 billion years ago. Until 1998, hundreds of domed formations were counted and their diameter ranged from 1.6 kilometers to 35 kilometers. They are hundreds of meters high and the inclination angle of the slopes is less than 5°. Some of them have secondary features such as depressions at their summits or ridges and they are redder than their surroundings (37).
Until the year 2000 it was common to distinguish between two areas of land on the moon, the dark area and the light area. Researchers from the Department of Earth Sciences and Planetary Sciences from the Center for Space Sciences presented an approach according to which there are 3 distinct regions on the moon, each region with its own geology. One area encompassing many of the basaltic maria has been named the Procellarum KREEP Terrane or PKT for short. In the "hot spots" there is a large concentration of thorium and other radioactive elements such as potassium and uranium. The term KREEP is an acronym for the phrase REE (Rare Earth Elements, (K) Potassium and P) (Phosphors.
As the magma ocean cooled, elements such as thorium were ejected from minerals that were in the stages of crystallization and created pockets of magma rich in KREEP that were located between the crust and the mantle. A concentration of heat-emitting elements below
Procellarum KREEP Terrane probably partly caused intense volcanism of the mare areas.
The mare regions were formed when hot radioactive elements melted minerals deep within the mantle and formed basaltic lava that erupted through fissures to the surface. over half the surface of the Procellarum KREEP Terrane) and was reshaped by the volcanism. The volcanic deposits were named "red spots" due to their spectral characteristics. Results of observations made by the LRO spacecraft confirmed the assumption that they are rich in silica. The red spots include part of the formation of domes that are also found within the boundaries of the PKT ( 24).
Seismology
Between 1964-1972, Apollo pilots placed seismometers at the landing sites. The places where the seismometers were placed are at the landing sites of Apollo 12, Apollo, 14, Apollo 15 and Apollo 17. They transmitted their data until 1977 when it was decided to stop their activity. It turned out that there are 4 types of earthquakes:
1. Earthquakes originating 700 kilometers below the surface caused by tides.
2. Ground vibrations caused by meteorite impacts.
3. Thermal quakes caused by the expansion of the frozen crust when every morning the surface is heated by sunlight, after a very cold night that lasts two weeks (a day on the moon lasts 28 earthly days).
4. Earthquakes originating at a depth of 20-30 kilometers underground.
The first three types of earthquakes are moderate and do not cause damage. The shallow earthquakes are weak. Between 1971-1972, 28 earthquakes with a magnitude of 5.5 were measured. on the Richter scale. The shallow earthquakes lasted 10 minutes each. In these cases the moon rang like a bell. Compared to the Earth, this is a long time. The duration of earthquakes on Earth is less than 2 minutes. The reason for this difference is that on Earth earthquakes are related to chemical weathering. The water weakens the stones and expands the structure of various minerals. When the energy is distributed along such compressed structures it acts like a foam and dampens the vibrations. The moon, on the other hand, is dry and cold and mostly hard like a block of stone or iron. The earthquakes vibrate like a tuning fork. Even if the earthquake is not strong, it lasts for a long time (38). Near the South Pole, an earthquake with a magnitude of 5.7 on the Richter scale was measured (39).
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