There are so many craters on the moon, why only craters are left? Where did the celestial body that hit it go?

It is no exaggeration to say that the moon is riddled with holes. Then how are so many potholes formed? If any celestial bodies or comets hit it, where did they go?

Let's take a look at the main landforms of the moon first.

volcanic vent

Crater can be said to be the most prominent feature of the lunar surface, covering almost the entire lunar surface. The largest crater is Bailey crater near the South Pole, with a diameter of 295 kilometers, which is a little larger than Hainan Island. A small crater may even be a hole of dozens of centimeters. There are about 33,000 with a diameter not less than 65,438+0,000 m, accounting for 7-65,438+00% of the lunar surface area.

1969, a Japanese scholar put forward the classification of craters, which can be divided into Cravey type (ancient craters are generally unrecognizable, and some craters contain mountains), Copernicus type (young craters often have "radial lines", and the inner wall generally has concentric sections and a central peak), Archimedes type (the ring wall is low, which may have evolved from Copernicus type).

female horse

The dark part of the moon seen by the naked eye is actually a vast plain on the moon. Then why is there a sea in the name? In fact, it was also because people thought that there might be water in this dark part. At present, there are 22 moon seas, and some landforms are called "Moon Sea" or "Moon-like Sea".

Most of the 22 recognized ones are distributed on the front of the moon. Three in the back and four on the side. On the front, the area of Moon Sea is slightly over 50%, of which the largest "storm sea" covers an area of about 5 million square kilometers, almost the sum of nine French areas. Most of the moon seas are generally round and oval, and most of them are surrounded by some mountains, but some seas are connected together. Besides the sea, there are five lakes with similar topography-Hu Meng, Dead Lake, Fox Xia, Qiuhu and Chun Hu, but some lakes are bigger than the sea. For example, Hu Meng has an area of 70,000 square kilometers, which is much larger than Qihai. The parts of the moon and the ocean that extend to the land are called "bays" and "swamps", and they are both distributed on the front. There are five bays: Luwan, Xiawan, Central Bay, Hongwan and Yue Mei Bay. There are three kinds of marshes: humus, epidemic marshes and dream marshes. Actually, there is no difference between a swamp and a bay.

The topography of the Moon Sea is generally low, similar to the basins on the earth. The moon sea is1-2km lower than the average moon horizon, and the southeast of the lowest sea is even 6000m lower than its surroundings. The albedo of the surface of the moon (a physical quantity of the brightness of reflected sunlight) is also relatively low, so it looks darker.

Moon, land and mountains

The area above the Moon Sea is called the Moon Land, which is generally 2-3 kilometers higher than the Moon Sea. Because of the high albedo, it looks brighter. On the front of the moon, the area of the moon land is roughly equal to that of the moon sea, but on the back of the moon, the area of the moon land is much larger than that of the moon sea. Isotope determination shows that the moon and land are much older than the moon and ocean, and they are the oldest landforms on the moon.

On the moon, in addition to many craters where dogs and teeth meet, there are some mountains similar to those on the earth. Mountains on the moon often borrow the names of mountains on the earth, such as Alps and Caucasus mountains. The longest mountain range is the Apennines, which stretches for 1000 km, but its height is only three or four kilometers higher than the moon horizon. There are also some steep peaks in the mountains, whose height was overestimated in the past. At present, it is believed that the heights of most peaks are similar to those of the earth, and the highest peaks (also near the south pole of the moon) are only 9000 meters and 8000 meters.

On the moon, there are 6 peaks over 6000 meters, 20 at 5000-6000 meters, 80 at 4000-5000 meters, and 200 at 1000 meters.

The mountains on the moon have a common feature: the slopes on both sides are asymmetrical, and the slopes on the seaward side are steep, sometimes cliff-shaped, while the other side is quite flat.

In addition to the high mountains, there are four cliffs hundreds of kilometers long on the moon. Three of them stand out in the Moon Sea, also known as the "Moon Graben".

Lunar radiation pattern

Another major feature of the moon's surface is that some younger craters often have beautiful "radiation patterns", which are bright belts extending in all directions with craters as radiation points, and they pass through mountains, the moon sea and craters almost in a straight line. The length and brightness of radiation patterns are different, and the most striking one is the radiation pattern of Tycho crater. The longest one is 1800 km long, which is especially spectacular at the full moon. Secondly, Copernicus and Kepler craters also have quite beautiful radiation patterns. According to statistics, there are 50 craters with radiation patterns.

The reason for the formation of radiation pattern is still inconclusive. Essentially, it is closely related to the theory of crater formation. At present, many people tend to say that meteorite impact may make high-temperature debris fly far on the moon, with no atmosphere and little gravity. Other scientists believe that the function of volcano is not ruled out, and the eruption of volcano may also form a flying radiation shape.

Moon Valley (Moon Gorge)

There are many famous rift valleys on the earth, such as the Great Rift Valley in East Africa. There is also such a structure on the surface of the moon-those seemingly winding black cracks are the Moon Valley, and some extend for hundreds of meters to Qian Qian meters, with widths ranging from several kilometers to tens of kilometers. Most of those broad moon valleys appear on the flat land of the moon, while those narrow and narrow moon valleys (sometimes called moon streams) can be seen everywhere. The most famous Moon Valley is the alpine Moon Valley connecting Yuhai and Leng Hai, which is located in the southeast of Plato's crater. It cut off the Alps on the moon, which is very spectacular. The photos taken from space are estimated to be 130 km long and 10- 12 km wide.

The formation of lunar craters

1) meteorite impact

Without the protection of the atmosphere, any meteorite will directly hit the moon as long as it is consistent with the path of the moon.

Because meteorites will release a lot of heat and energy when they hit the moon at a very high speed, they will melt quickly at this time, so there will be many craters without meteorites on the moon.

Then why are there so many craters left on the moon? This has to start with the structure of the moon. Because of the lack of atmospheric activity on the moon. Plus the special geology of the moon. So the crater is well preserved. According to the origin of the moon, the moon hit the primitive earth and then smashed it into many pieces. So the moon in space was formed. Because the moon has no atmospheric protection, craters can be well preserved.

2) the influence of solar storms

Some scientists say that many high-energy particles emitted by solar storms are collected in the back area of the moon, and charges will accumulate in the lunar soil (also known as floating soil layer). When these charges accumulate to a certain extent, it will trigger a micro-explosion, and the charges will suddenly penetrate the soil. They estimate that 10-25% of the top dust explodes in this way, because the temperature on the back of the moon is lower, and the charge is easier to accumulate.

Permanently dark areas on the moon may be more active than previously thought. Although these areas are not directly illuminated and hit by sunlight or solar wind, they may still be hit by meteors like other parts of the lunar surface.

They are also irradiated by penetrating particles, and the floating soil in the permanent dark area has extremely low temperature, so its conductivity is extremely low and it will discharge for a long time. This makes the large-scale solar high-energy particle explosion charge the 1mm soil on the topsoil, reaching the dielectric breakdown point. "

Since it is dielectric breakdown, it is nothing.