There are three main schools of thought on the origin of the Moon, but they are still undecided. Some scientists believe that the Moon was formed 4.6 billion years ago from cosmic gases and dust, as was the Earth; others believe that the Moon is a child of the Earth, split off from it. However, the data brought back by Helios on several occasions show that the composition of the Moon and the Earth are very different. Many scientists believe that the Moon was accidentally sucked into the gravitational pull of the Earth many years ago, and thus accidentally incorporated into the Earth's orbit. But others cite celestial mechanics to argue against this.
Moon older than Earth:
Scientists were surprised to learn that 99 percent of the rocks brought back from the moon are older than 90 percent of the oldest rocks on Earth. Moon rocks brought back by astronauts have been dated to be 4.3 billion to 4.6 billion years old, which is equivalent to the history of the solar system.
Soil is older than rock:
The Sea of Tranquility, where American astronauts first landed, has soil older than rock. The difference between the two has been analyzed to be as much as 1 billion years. Chemical analyses show that the soil on the moon did not evolve from rocks, but may have come from somewhere else.
Impacts make loud noises:
Solaris hit the moon's surface during its explorations, and when the lunar lander and rockets returned. But each time, the moon rang like a big gong or bell, and during the Apollo 12 exploration, the moon's echoes lasted for four hours, a phenomenon that no scientist has been able to explain.
Black shadow area has rare metals:
When you look at the moon on Earth, you will see some black shadows, the astronauts landed on this plain-like black shadow area, found it difficult to drill holes in its surface, after researching the soil samples here contain metal elements such as titanium, berkelium, yttrium, etc., the scientists were very surprised, because these metal elements to be in the rather high heat ---- Celsius 6000 degrees or more before melting. 6,000 degrees Celsius or more before they could melt and mix with the surrounding rock.
Pure iron particles don't rust:
Rock samples brought back by astronauts from the moon contained particles of pure iron, which scientists believe did not come from meteorites. Some experts report that the iron particles have not rusted for years since they were brought back to Earth, the first time that pure iron has ever been seen in the scientific community.
Surface as smooth as a mirror:
Many parts of the Moon's surface are as smooth as a mirror. It seems to have been "scalded" by some unknown source of heat. Experts say this was not caused by a huge meteorite impact, and some scientists believe the heat from the sun was the main factor.
Shocked by magnetism:
Early studies of the moon said it had no magnetic field, but in recent years, after analyzing the moon's rocks, it became clear that they were strongly magnetic. However, if the Moon's rocks really had a magnetic field, there would be a core of iron, but now information tells us that such a huge hot core could not exist inside the Moon, nor could it have gotten its magnetic properties from the Earth's magnetic field, because the Moon would have to be very close to the Earth in order to get its magnetic properties from the Earth, and if it were, it would be destroyed by the force of the Earth's core.
Concentrate at the bottom of the crust:
Space probes have brought back information showing that the moon's crust has large chunks of concentrate underneath it, and there is also a force of attraction that makes the spacecraft tilt as it passes by. All scientists knew was that the concentrate was a heavy, dense substance, but nothing more.
Physical Characteristics
Equatorial Diameter 3,476.2 kilometers
Polar Diameter 3,472.0 kilometers
Obliquity 0.0012
Surface Area 3.976×107 square kilometers
Obliquity 0.0012
Volume 2.199×1010 cubic kilometers
Mass 7.349×1022 kg
Mean density 3.350 times that of water
Gravitational acceleration at the equator 1.62 m/s2
1/6th that of the Earth
Escape velocity 2.38 km/s
Rotation period 27 days, 7 hours, 43 minutes, and 11.559 seconds
(Synchronized rotation)
Rotation speed 16.655 m/s (at the equator)
Inclination of rotation axis varies between 3.60° and 6.69°
(angle of intersection with the ecliptic is 1.5424°)
Albedo 0.12
Observable magnitude at full moon -12.74
Surface temperature (t) -233 ~123 °C (mean -23 °C)
Atmospheric pressure 1.3 × 10-10 kPa
The Moon orbits the Earth in about one lunar month while moving half a degree per hour relative to the background stars, i.e., about the same apparent diameter as the lunar surface. Unlike other satellites, the Moon's orbital plane is closer to the ecliptic than to the Earth's equator.
The time it takes for the Moon to orbit the Earth (lunar rotation) for one week relative to the background stars is called a sidereal month; and the time between a new moon and the next new moon (or between two identical moon phases) is called a lunation. The lunation is longer than the sidereal month because the Earth itself advances some distance in its orbit around the Sun during the Moon's orbit.
Because the Moon's rotation period is exactly the same as its revolution period, we can only see the Moon always facing the Earth in the same direction. Since the early days of its formation, the Moon has been subjected to a torque that causes its rotation to slow down, a process called tidal locking. As a result, part of the angular momentum of the Earth's rotation is converted into the angular momentum of the Moon's revolution around the Earth, with the result that the Moon is moving away from the Earth at a rate of about 38 millimeters per year. At the same time, the Earth's rotation is getting slower and slower, and the length of the day is getting longer by 15 microseconds per year.
The gravitational pull of the Moon on the Earth is one of the causes of tidal phenomena. The Moon's orbit around the Earth is synchronous, and the so-called synchronous rotation is not strict. Because the moon orbit is elliptical, when the moon is in perihelion, its rotation speed will not catch up with the rotation speed, so we can see the eastern part of the moon surface up to 98 degrees east longitude, on the contrary, when the moon is in aphelion, the rotation speed is faster than the rotation speed, so we can see the western part of the moon surface up to 98 degrees west longitude area. This phenomenon is called libration. Since the Moon's orbit is inclined to the Earth's equator, the polar regions of the Moon make a wobble of about 7 degrees when the Moon moves in the starry sky, a phenomenon known as libration. Furthermore, since the Moon is only 60 Earth radii away from the Earth, if the observer observes from moonrise to moonset, the observation point will have a displacement of one Earth diameter, and the area of one degree of longitude on the Moon's surface can be seen more often. This phenomenon is called scale movement.
Strictly speaking, the Earth and the Moon orbit around the *** homogeneous center of mass, which is 4,700 km from the center of the Earth (i.e., 2/3 of the Earth's radius). Because the *** center of mass is below the Earth's surface, the Earth's motion around the *** center of mass seems to be "wobbling" in general. Viewed from the north pole of the earth, the earth and the moon both rotate in a clockwise direction; and the moon also orbits around the earth in a clockwise direction; even the earth rotates around the sun in a clockwise direction.
Many people do not understand why the values of the inclination of the Moon's orbit and the inclination of the Moon's rotation axis vary so much. In fact, the orbital inclination is relative to the central body (i.e., the Earth), while the rotational axis inclination is relative to the orbital plane of the satellite (i.e., the Moon) itself. While this definitional convention is well suited to the general case (e.g., the orbit of an artificial satellite) and is fairly constant in value, this is not the case for the Moon.
The Moon's orbital plane (the plane of the White Way) maintains an angle of 5.145 396° with the ecliptic (the plane of the Earth's rotational orbit), while the Moon's axis of rotation is at an angle of 1.5424° to the normal to the ecliptic. Because the Earth is not perfectly spherical, but is more elevated at the equator, the leucopause is in constant motion (i.e., the intersection with the ecliptic rotates clockwise), completing one week every 6793.5 days (18.5966 years). During this period, the angle of the White Way Plane with respect to the Earth's equatorial plane (which is inclined to the ecliptic at 23.45°) varies from 28.60° (i.e., 23.45° + 5.15°) to 18.30° (i.e., 23.45° - 5.15°). Similarly, the angle between the Moon's rotation axis and the white channel plane varies between 6.69° (i.e. 5.15° + 1.54°) and 3.60° (i.e. 5.15° - 1.54°). These changes in the Moon's orbit in turn affect the inclination of the Earth's rotation axis, causing it to oscillate by ±0.002 56°, known as the Chapter Motion.
The two points of intersection between the white and ecliptic planes are known as the lunar nodes -- the ascending (northern) node, through which the Moon passes north of the ecliptic plane, and the descending (southern) node, through which the Moon passes south of the ecliptic. A solar eclipse occurs when the new Moon is exactly on the nodes, and a lunar eclipse occurs when the full Moon is exactly on the nodes;
Period of the Moon Name Value (d) Definition
Sidereal Moon 27.321 661 Relative to background stars
Lunar Moon 29.530 588 Relative to the Sun (lunar phases)
Equinox Moon 27.321 582 relative to the equinoxes
Perigee Moon 27.554 550 relative to the perigee
Node Moon 27.212 220 relative to the ascending node
Other features of the Moon's orbit Name Numerical value (d) Definition
Remaining phase/day 19 years
Mean month Perigee distance ~364,397 km
Apogee distance ~406,731 km
Mean orbital eccentricity 0.0549003
Node recession period 18.61 yrs
Perigee kinematics period 8.85 yrs
Eclipse year 346.6 days
Repeat eclipses 18 years, 10/11 days
Mean inclination of orbit to the ecliptic 5°9'
Mean inclination of the Moon's equator to the ecliptic 1°32'
Human exploration of the Moon:
The first manmade object to reach the Moon was the unmanned Soviet Lunar lander Lunar 2. It crashed into the lunar surface on September 14, 1959 . Luna 3 photographed the backside of the moon on October 7 of the same year. Luna 9 was the first soft-landing vehicle on the Moon, and on February 3, 1966, it returned photos taken from the lunar surface. In addition, Luna 10 was successfully orbited on March 31, 1966, becoming the first artificial satellite on the Moon.
During the Cold War, the United States of America and the former Soviet Union wanted to stay ahead of each other in space technology. This space race came to a climax on July 20, 1969, when the first man landed on the moon. Neil Armstrong, commander of Apollo 11 in the United States of America, was the first man to set foot on the Moon, while Eugene Cernan, a member of the December 1972 Apollo 17 mission, was the last man to stand on the Moon. See: List of Lunar Astronauts
The Apollo 11 astronauts left a 9-inch by 7-inch stainless steel plaque on the surface of the Moon to commemorate the landing and to provide some information about the potential discovery of other life on it.
The plaque is depicted on both sides of the Earth and is signed by the three astronauts and by then-President Nixon of the United States of America.
Six Helios missions and three unmanned Luna missions (Luna 16, 20, 24) brought rock and soil samples from the moon back to Earth.
In February 2004, the President of the United States of America, George W. Bush, proposed to send a man back to the Moon by 2020. The European Space Agency (ESA) and the People's Republic of China (PRC) also have plans to launch probes to the Moon. The European Smart 1 probe was launched on September 27, 2003, and on November 15, 2004, it entered orbit around the Moon. It will survey the lunar environment and produce X-ray maps of the lunar surface.
The People's Republic of China has also been actively pursuing a lunar exploration program and seeking the feasibility of exploiting the Moon's resources, in particular the helium isotope helium-3, which is expected to be a future source of energy for the Earth. For information on the People's Republic of China's lunar exploration program, see the Chang'e Project entry.
Japan and India are not far behind. Japan has already set out a preliminary mission for future lunar exploration. Japan's Aerospace Exploration Agency (Aerospace Research and Development Agency) has even begun planning for a manned lunar base. India will launch Chandrayan, an unmanned lunar probe, first.
Myths about the moon:
In the ancient mythology of the People's Republic of China, there are countless stories about the moon. In ancient Greek mythology, the name of the goddess of the moon was Artemis, who was the twin sister of Apollo, the god of the sun, and she was also the goddess of hunting. The astronomical symbol of the moon resembles a curved crescent, symbolizing Artemis' sacred bow.
The Moon is the Earth's only natural satellite and is the closest celestial body to us, with an average distance from the Earth of about 384,401 kilometers. Its average diameter is about 3,476 kilometers, which is slightly larger than 1/4 of the Earth's diameter. The surface area of the Moon is 38 million kilometers, which is not as large as the area of our Asia. The mass of the Moon is about 735 billion billion tons, equivalent to 1/81 of the mass of the Earth, and the gravity on the surface of the Moon is almost equivalent to 1/6 of the gravity of the Earth.
Orbital Motion of the Moon The Moon orbits the Earth in an elliptical orbit. This orbital plane intercepts a large circle on the celestial sphere called the "white channel". The plane of the white channel does not coincide with the celestial equator, nor is it parallel to the ecliptic plane, and its position in space is constantly changing.
Cycle 173 days.
Rotation of the Moon The Moon rotates at the same time as it orbits the Earth, with a period of 27.32166 days, which is a sidereal month, so we cannot see the back of the Moon. This phenomenon, which we call "synchronized rotation", is almost universal in the satellite world
. It's generally thought to be the result of the long-term tidal action of the planets on the satellites. The libration is a wonderful phenomenon that allows us to see 59% of the moon's surface. The main reasons for this are:
1. the mismatch of rotational velocity and rotational angular velocity in different parts of the elliptical orbit. 2. the angle of intersection of the White Way and the Equator.
Physical Condition of the Moon - The main topography of the lunar surface is:
Crater The name was given by Galileo. It is a prominent feature of the lunar surface and covers almost the entire surface. The largest crater is Bailey's Crater near the South Pole, which is 295 kilometers in diameter, a little larger than Hainan Island. Smaller craters
may even be a crater of a few tens of centimeters. There are about 33,000 that are no smaller than 1,000 meters in diameter. That's 7-10% of the moon's surface area.
A Japanese scholar proposed a classification of craters in 1969, which is divided into the Clavian type (old craters, generally all
face, some still have mountains within mountains), the Copernican type (young craters, often "radial lines", the inner wall is generally with
concentric circles of segments, the center generally have a central peak), the Copernican type (young craters, often "radial lines", the inner wall is generally with
segmental mounds, and the center generally have a central peak). (the inner wall usually has a concentric segmental mound, the center usually has a central peak) Archimedean (lower ring wall, probably evolved from Copernican) Bowl and Dimple (small craters, some less than a meter in diameter).
The dark part of the Moon's surface seen by the naked eye is actually a vast plain on the surface of the Moon. For historical reasons, this misnomer has survived to the present day.
There are 22 identified lunar seas, in addition to some terrains known as "lunar seas" or "lunar-like seas". The vast majority of the 22 recognized are on the front side of the Moon. Three are on the backside and four are on the fringes. On the front side of the moon sea area slightly more than
50%, of which the largest "stormy ocean" area of more than five million square kilometers, almost nine France's area combined. Most of the lunar seas are roughly circular, oval, and surrounded by mountain ranges, but some are
continuous. In addition to the "sea", there are five terrain and similar "lake" ---- dream lake, dead lake, summer lake, autumn lake, spring lake, but some lakes than the sea is also large, such as the dream lake area of 70,000 square kilometers, than the sea of steam and so on, but also much larger
More. The parts of the Moon Sea that reach out to the land are called "bays" and "marshes," and they are located on the front side. There are five bays: Dew Bay, Summer Bay, Central Bay, Rainbow Bay, and Eyebright Bay; and three marshes: Rotten Marsh, Epidemic Marsh, and Dream Marsh, but there is no difference between a marsh and a bay.
The terrain of the Moon Sea is generally low, similar to the Earth's basin, the Moon Sea is 1-2 kilometers lower than the average level of the Moon,
The southeastern part of the lowest individual sea of the Sea of Rain is even 6000 meters lower than the surrounding area. The lunar surface also has a lower albedo (a physical measure of the ability to reflect sunlight), making it appear darker.
Lunar land and mountains The area of the Moon above the lunar sea, called the lunar land, is generally 2-3 kilometers above the level of the lunar sea, and appears brighter because of its high albedo. On the front side of the Moon, the area of the Moon's landmass is roughly equal to that of the Moon's sea
But on the back side of the Moon, the landmass is much larger than the Moon's sea. It is known from isotope measurements that the lunar land is much older than the lunar sea, and is the oldest topographic feature on the Moon.
On the Moon, in addition to the many craters that dog-ear the Moon, there are also mountain ranges that are similar to those on Earth. The mountains on the Moon often borrow the name of the mountains on Earth, such as the Alps, the Caucasus Mountains, etc., of which the longest mountain range is the Apennine Mountains, stretching 1000 kilometers, but the height is only higher than the lunar sea level of three or four kilometers. There are also some high peaks in the mountain ranges, but their heights were overestimated in the past. It is now believed that the height of most peaks is similar to that of the Earth's peaks, and that the highest peaks (which are also near the south pole of the Moon) are only 9,000 and 8,000 meters high.
There are six peaks above 6,000 meters on the lunar surface, 20 between 5,000 and 6,000 meters, 80 between 4,000 and 5,000 meters, and 200 above 1,000 meters.
The mountains on the Moon have a common feature: their slopes are very asymmetrical, with the seaward side being very steep and sometimes cliff-like, while the other side is fairly gentle.
In addition to mountain ranges and clusters, there are four cliffs on the surface of the Moon that are hundreds of kilometers long. Three of these cliffs protrude into the Moon's sea, and are also known as "lunar rifts".
Radials on the Moon Another major feature of the Moon's surface is that some of the "younger" craters often have beautiful "radials", bright bands of light extending in all directions from the craters as radials, which run almost straight through the mountain system, the lunar sea, and the craters. This is a bright band that extends in all directions from the craters as radial points and runs in an almost straight direction through the mountain system, the lunar sea and the craters. Radials vary in length and brightness, the most striking being that of the craters of the Tigrinya Valley, the longest of which is 1,800 kilometers long and is particularly spectacular at full moon. The second two craters, Copernicus and Kepler, also have quite beautiful radiating lines. According to statistics, there are 50 craters with radiation patterns.
The reason for the formation of the radiation pattern is still not conclusive. In essence, it is closely related to the theory of crater formation. Many now favor the meteorite impact theory, which suggests that on a moon with no atmosphere and little gravity, a meteorite impact could have sent hot debris far away. Other scientists believe that volcanoes cannot be ruled out, and that eruptions could have created radiant shapes that flew around.
Valley of the Moon (Moon Gap) The Earth has many famous rift valleys, such as the Great Rift Valley in East Africa. The Moon's surface also has such formations ---- The large black cracks that appear to be curved are lunar valleys, some of which stretch from hundreds to thousands of kilometers, and range in width from a few kilometers to several tens of kilometers. The wider valleys are mostly found in the flatter areas of the lunar landscape, while the narrower, smaller valleys (sometimes called lunar streams) are found everywhere. The most famous of these valleys is the Great Alpine Valley, which links the Rainy and Cold Seas southeast of Plato's Crater and cuts off the Alps from the surface of the Moon in a spectacular fashion. Photographs taken from space estimate it to be 130 kilometers long and 10-12 kilometers wide.
Where did it come from?
The moon is a spacecraft of aliens: this is not nonsense, because the power of science lies in the bold imagination, there will be no new breakthroughs without creativity, and the theory of relativity put forward by Albert Einstein at that time was not nonsense. What the Chinese lack in science is this boldness of vision.
Why we can't see the back of the moon
The moon always faces the earth in one direction. It's because the moon has the same period of autorotation and revolution. (Day 27.32166)
To understand this phenomenon, you can do an experiment. Draw a circle and mark the directions east, west, south, north and west. You stand at the center of the circle (representing the Earth), and find a friend who will stand on the circle and move counterclockwise along the circle with his face facing forward (i.e., without craning his neck), and ask him to keep his face toward the center of the circle, i.e., you, as he moves along the circle. So this process basically simulates the process of the moon spinning on the earth.
Obviously, in such a process, your friend is always facing you. Here's why, in such a process, the rotation period is equal to the spin period.
Your friend starts from your due north, rotates around you, and when he appears due north again, he completes one rotation cycle. (Similar to the time it takes for the moon to rotate around the earth.)
Let's see what his rotation time is. Let's also set your friend's initial pose when he is in your north position, with his face facing south.... Then we can see that when your friend moves counterclockwise to your west position, his spinning attitude is rotated 90 degrees counterclockwise. (If your friend does not "rotate" during the process, then when he is in this position, he is not facing you, but is still facing south. In the actual experiment, your friend was facing east, so he rotated 90 degrees counterclockwise from his initial position.
Similarly, when he walked south of you, he rotated himself 180 degrees from his initial position. When he walks due east of you, he self-propagates 270 degrees from his initial position. When he walks north of you again, he's traveled 360 degrees from his initial attitude. This means that he has completed one rotation cycle.
Because the completion of a revolution is the same as the completion of a rotation, the rotation period is equal to the rotation period in terms of time. Because during the whole process, your friend always faces you with his body face, that is to say, the moon always faces the earth with one face.
Guanghan Palace - the moon
Whenever the night falls, a round of bright moon rises in the night sky, clear moonlight sprinkled all over the earth, so that people produce countless feelings of reverie. Literati and writers are even more favorable to the moon, the Tang Dynasty poet Zhang Ruoxu's "the river where the moon is seen for the first time, the river where the moon is illuminated at the beginning of the year," as well as the Song Dynasty writer Su Shi's "When will the moon be there, ask for the blue sky with a glass of wine," which can be called the popular aria of the moon.
The moon is commonly known as the moon, also known as Taiyin. In ancient Chinese mythology, there are countless stories about the moon. In ancient Greek mythology, the name of the goddess of the moon was Artemis, and she was also the goddess of hunting. The astronomical symbol of the moon resembles a curved ebony eyebrow and symbolizes Artemis' sacred bow.
When the moon is in the sky, we can clearly see that it has dark and bright areas. Early astronomers, when observing the Moon, thought that the dark areas were covered with sea water and called them "seas". Famous ones are the Sea of Clouds, the Sea of Wetness, and the Sea of Tranquility. The bright part is the mountains, which are dotted with craters and mountain ranges. Bailey's crater, located near the South Pole, is 295 kilometers in diameter and could fit the entire island of Hainan. The deepest crater is Newton's Crater, which is 8,788 kilometers deep. In addition to craters, there are also ordinary mountain ranges on the lunar surface. High mountains and deep valleys appear on top of each other.
The age of the Moon is also about 4.6 billion years, and it is closely related to the Earth. The Moon also has a layered structure of shell, mantle and core. The average thickness of the outermost lunar crust is about 60 to 65 kilometers. Below the crust, at a depth of 1,000 kilometers, is the mantle, which accounts for most of the volume of the Moon. Below the mantle is the nucleus, which has a temperature of about 1,000 degrees Celsius and is probably in a molten state. The diameter of the Moon is about 3,476 kilometers, which is 3/11 of the Earth's. The volume is only 1/49 of the Earth's, the mass is about 735 billion billion tons, which is equivalent to 1/81 of the Earth's mass, and the gravity at the surface of the Moon is almost equivalent to 1/6 of the Earth's gravity.
The Moon's formation is based on the following points of view.
I. Splitting theory. This is one of the earliest hypotheses to explain the origin of the Moon. As early as 1898, George Darwin, the son of the famous biologist Darwin, pointed out in his article "Tides and Similar Effects in the Solar System" that the moon was originally a part of the earth, and then due to the earth's rotating speed was too fast, threw a part of the earth's material, which was detached from the earth to form the moon, and the big crater left on the earth was the present Pacific Ocean. This viewpoint soon received opposition from some people. They argued that the Earth could not have thrown out such a large piece of material at the speed of its rotation. Besides, if the moon was thrown out by the earth, then the material composition of the two should be the same. However, through the "Apollo 12" spacecraft from the moon to bring back rock samples for laboratory analysis, found that the two are very far from each other.
II. Capture theory. This hypothesis that the moon was originally just an asteroid in the solar system, once, because of orbiting near the Earth, was captured by the Earth's gravity, and never left the Earth. There is also a view close to the capture theory that the Earth kept accreting material that came into its orbit, and over time, more and more was accreted, eventually forming the Moon. But others point out that for a planet as large as the Moon, the Earth might not have had the power to capture it.
Three. The theory of homology. According to this hypothesis, both the Earth and the Moon are floating nebulae in the solar system, which were rotated and accreted to form a star at the same time. In the process of accretion, the Earth is correspondingly faster than the Moon and becomes the "older brother". This assumption has also been challenged by the existence of an objective. Through laboratory analysis of rock samples brought back from the Moon by the Apollo 12 spacecraft, it was found that the Moon is much older than the Earth. It is thought that the moon should be at least 7 billion years old.
Four. The Great Collision theory. This is a new hypothesis on the cause of the moon in recent years. March 20, 1986, held in Houston Johnson Space Center, the moon and planetary seminar, the United States of America, Los Alamos National Laboratory, Benz, Slattery and Harvard University Smith Center for Astrophysics of the Cameron *** with the proposed big collision hypothesis. This hypothesis suggests that early in the evolution of the solar system, a large number of "stars" were formed in interstellar space, and that the stars grew up by colliding with each other and accreting. The stars merged to form a primordial Earth, and at the same time an object equal to 0.14 times the mass of the Earth was formed. During their respective evolutionary processes, these two objects formed a metallic core dominated by iron and a mantle and shell composed of silicates. Since these two celestial bodies are not far from each other, the chances of an encounter are high. By chance, the smaller object crashed into the Earth at a speed of about 5 kilometers per second. The violent collision not only changed the motion of the Earth, so that the axis of the Earth tilted, but also the small object was broken by the impact, the silicate shells and mantle heat evaporation, the expansion of the gas as well as a large speed to carry a large number of crushed dust flew away from the Earth. The material that flew away from the Earth consisted mainly of the mantle of the colliding body and a small portion of material from the Earth, in the ratio of roughly 0.85:0.15. The metal nuclei that separated from the mantle at the time of the rupture of the impacting body were slowed down by the expanding away gases, and were accreted to the Earth in about four hours. The gases and dust that flew away from the Earth were not completely out of the Earth's gravitational control, and they combined by mutual accretion to form either a fully molten moon, or several small separated moons that were first formed, and then gradually accreted to form a large partially molten moon.
Moon composition
Four and a half billion years ago, the moon's surface was still a liquid magma ocean. Scientists believe that the minerals that make up the Moon, called kreep minerals (KREEP), show chemical clues left behind by the magma ocean. KREEP is actually a composite of what scientists call "incompatible elements" - substances that could not make it into the crystal structure, were left behind, and floated to the surface of the magma. KREEP is actually a composite of what scientists call "incompatible elements"-substances that can't enter the crystal structure and float to the surface of magma. For researchers, KREEP is a handy clue to the history of volcanism on the moon's crust, and can be used to speculate on the frequency and timing of impacts by comets or other celestial bodies.
The lunar crust is made up of several major elements, including uranium, thorium, potassium, oxygen, silicon, magnesium, iron, titanium, calcium, aluminum and hydrogen. Each element emits specific gamma radiation when bombarded by cosmic rays. Some elements, such as uranium, thorium and potassium, are already radioactive and can emit gamma radiation on their own. But whatever the cause, each element emits different gamma rays, each with a unique spectral signature that can be measured with a spectrometer.
Until now, the abundance of the moon's elements has not been measured comprehensively. Measurements from current spacecraft are limited to a portion of the lunar surface.
References: