Below the moon shell to 1000 km is the moon mantle, and some people limit the lower part of the moon mantle to 1388 km. The mantle of the moon accounts for more than half of the volume of the moon, and is mainly composed of basic rocks and ultrabasic rocks equivalent to the earth. The density of materials generally exceeds 3.5 grams per cubic centimeter, and the lower layer may be slightly lower by 5%. The center of the moon is the moon core from the bottom of the moon mantle to the depth of 1740 km, which is mainly composed of iron, nickel and sulfur. The temperature of the lunar core is roughly between 1000 degrees Celsius and 1600 degrees Celsius.
1956101On October 26th, an astronomer found that the alfin crater in the photo became blurred. This may be because the volcano is erupting, and the emitted gas blurs its outline. 1 958165438+1October 3, another astronomical discovery was made that the central peak in the crater presented an unusual scenery, and the crater was red, and then the brightness of the central peak suddenly increased by almost1times. There are signs that this is a volcanic eruption. 1959, 10 year123 October, the volcanic eruption of alfin crater was observed again, and the scale of this activity was much larger than that of a year ago.
According to the records of the automatic lunar seismic station established by astronauts on the moon, lunar earthquakes often occur on the moon. The lunar seismograph once measured 10000 lunar earthquakes. In addition, long-term observation also found that some small craters on the moon, such as the famous forest craters, have gradually shrunk and disappeared, leaving only a white spot, while some craters are getting bigger and bigger.
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General situation of the moon
First, the basic parameters of the moon:
Average equatorial radius: ae = 1738000.
Average radius: a = 1737400 meters.
Equatorial gravity acceleration: Ge = 1.6 18m/s 2.
Average rotation period: T = 27.32 166 days.
Flatness: f = 0.006
Mass: m ⊕ = 0.07348×1024kg
Gravity constant of lunar center: GM = 4.90793455×1012m3/S2.
Average density: ρ e = 3.34g/cm3.
The mass ratio of the earth-moon system E/M = 8 1.30068.
Average distance from the earth: r = 384,400km.
Escape velocity: v = 2.38/s.
Surface temperature: t =- 120 ~+ 150.
Ground atmospheric pressure: p =1.3×10-10 Pa.
Second, the circle structure
The moon is the only natural satellite of the earth and has a close evolutionary relationship with the earth. According to the analysis of the recorded data of Apollo 1 1 2 and the study of the moon surface and moon rocks, it is known that the moon today has a circular structure, but it is not exactly the same as the earth. There is a layer of lunar soil several meters to several tens of meters thick on the surface of the moon. The whole moon can be considered to be composed of lunar lithosphere (0 ~ 1000 km), asthenosphere (1000 ~ 1600 km) and lunar core (1600 ~ 1738 km). The lunar lithosphere can be further divided into four layers, namely, the lunar crust (0 ~ 60 km), the last lunar mantle (60 ~ 300 km), the mid-moon mantle (300 ~ 800 km) and the lunar seismic belt (800 ~ 1000 km). The asthenosphere is also called the next moon curtain. At the depths of the lunar shell 10 km, 25 km and 60 km, the wave velocity of the lunar earthquake changes sharply, indicating that there is obvious discontinuity at these depths. The surface of the moon is composed of basalt. The first lunar crust is 25 kilometers deep, and the second lunar crust is composed of gabbro and anorthite between 25 kilometers and 60 kilometers. Last month's mantle was composed of olivine rich in magnesium, while the mid-month mantle and the next month's mantle were composed of basic rocks. The focal position of the moon is between 600 ~ 1000 km, and the average focal depth of the moon is 800 km. Because the density of rocks on the surface of the moon is not much smaller than the average density of the whole moon, it can be considered that the moon core is not made of heavy elements such as iron and nickel, but may be plastic or partially melted. At the depth of 1000 km on the moon, the temperature of the lunar mantle will not be higher than1000 C. According to the understanding of the internal situation of the moon, the solid part of the circle structure is not unique to the earth itself. The above structure of the lunar sphere is also the result of the differentiation of the whole lunar material sphere during the evolution of the moon.
Third, the characteristics of the lunar surface
On the moon, the mountains are undulating, the peaks are densely covered, there is no water, and the atmosphere is extremely thin, and the atmospheric density is less than one trillion times the sea level of the earth. No volcanic activity, no life. This is a peaceful world. It is known that there are 22-month seas with a total area of 5 million square kilometers. Seen from the earth, there are 10 big moon seas: storm sea, rain sea, sea of clouds, wet sea and steam sea in the east, and dangerous sea, Chenghai sea, Jinghai sea, Fengfuhai sea and Jiuhai sea in the west. These Moon Seas are full of lava erupting from the interior of the Moon, and the craters of some Moon Seas basins are also covered by erupting lava, forming a large-scale dark lava plain. Therefore, the formation of the Moon Sea Basin and the subsequent lava eruption constitute one of the most important events in the evolution history of the Moon.
Craters on the moon, also known as craters, are the most obvious features on the moon. Crater, which means "bowl" in Greek, is also called bowl-shaped pit structure. There may be two reasons for the formation of craters, one is the result of meteorite impact, the other is volcanic activity; But most of the ring structures are the result of meteorite impact. 1924, A.C. Gifford compared the lunar crater with the crater on the earth and confirmed that the lunar crater was formed by the impact of meteorites. Therefore, meteorite impact is one of the main functions to form the surface morphology of the moon today. Many large craters are surrounded by radial stripes, which are made of high reflectivity materials, forming undulating terrain that can extend for hundreds of kilometers. There is a coating formed by sputtering materials around the crater; Splashed rocks hit the surface of the moon again, forming a second crater. Due to repeated meteorite impacts and rock splashes, as well as a large amount of magma ejected by the moon, many craters become blurred, or only the peak in the center of the crater is exposed on the surface covered by magma.
Judging from the condition of craters superimposed on the moon sea and the radioactive age determination of samples brought back from the moon, it shows that the moon sea material and craters formed at roughly the same time. The age of the Moon Sea is about 3.5 billion years, and the formation of the lunar highland existed at least 654.38+billion years before the eruption of lava in the Moon Sea, so the original lunar shell was formed earlier, which was the result of the continuous eruption of a large number of lava and the long-term division of lunar materials. The research shows that the spherical structure of the moon lasted for about 654.38+0 billion years after a long astronomical evolution stage of about 4.6 billion years ago. Many large craters on the moon are named after ancient and modern astronomers, such as Copernicus, Kepler, Eratosthenes, Ptolemy and Tycho. The crater on the surface of the moon is nearly 100 km in diameter, but only 10 cm. There are as many as 33,000 craters with a diameter greater than 1 km, accounting for 7 ~ 10% of the surface area of the moon. The largest crater on the moon is 235 kilometers in diameter. On the side of the moon facing away from the earth, there are dense craters, but the area occupied by the moon sea is small, and the thickness of the moon shell is thicker than that of the front, with the thickest point reaching 150 km and the thickness of the front moon shell about 60 km. Due to the lack of atmosphere and hydrosphere on the lunar surface, the morphological characteristics of the lunar surface formed by lava eruption and meteorite impact in the early moon can be preserved for a long time. Since 1969, astronauts have retrieved hundreds of kilograms of lunar rocks from the surface of the moon. Through the study and analysis of these moon rocks, it is considered that these moon rocks have melted and the surface material of the moon is mainly composed of magmatic rocks. The moon is at least 4.6 billion years old.
Fourth, the movement of the moon.
The earth and the moon form a celestial system called earth-moon system. In the Earth-Moon system, the earth is the central celestial body, so the movement of earth-moon system is generally described as the movement of the moon around the earth. However, the actual motion of earth-moon system is that the earth and the moon revolve around their common center of mass. The time for the Earth and the Moon to rotate around their common center of mass is 27 days, 7 hours and 43 minutes 1 1.6 seconds, that is, 27.32 166 days. The common center of mass is located in the earth body about 467 1 km from the center of the earth.
There are interactions between celestial bodies in the universe, and the so-called "tidal interaction" is one of the important forms of interaction. Because the distance between the earth and the moon is relatively close, this tidal effect is more obvious. Among the celestial bodies in the solar system, the tidal effect of the moon on the earth is about 2.2 times that of the sun, and it is much greater than other celestial bodies. Because of the tidal friction of the moon, the earth's rotation slows down, the daily time becomes longer, and the average length of a day increases by nearly two thousandths of a second every one hundred years. At the same time, due to the slow rotation of the earth, the moon slowly spirals outward. At present, the moon is moving away from the earth at a speed of 3 ~ 4 cm per year. Similarly, the earth's tidal action on the moon makes the moon's rotation period the same as its period of revolution. The rotation and revolution of the moon is from west to east. This rotation of the moon is called synchronous rotation. Therefore, since ancient times, people have always seen the moon facing the same direction of our earth.
When humans began to record the history of the earth, they had already measured the time by observing the position and phase of the moon. By studying the periodic movements of the moon and the sun, ancient China and Mesopotamia established calendars. By 300 BC, astronomers in Babylon had been able to predict solar eclipses.