Knowledge about meteorites 1. Meteors and meteorites Meteors are a natural phenomenon. In the space near the earth, in addition to planets, there are also many interstellar substances. These interstellar substances are as small as dust. They are as big as a mountain. They rotate around the sun in space and move according to their own speed, orbit and certain revolution period. These interstellar materials can also be called meteoroids. They do not emit light themselves. They usually orbit the sun at a speed of tens of kilometers per second and form an elliptical orbit. When they intersect with the Earth's spherical orbit, they have a chance to form meteoroids. The earth's revolution speed reaches more than 30 kilometers per second, and the speed of meteoroids is faster than that of the earth. If the meteoroids come head-on, they will pass through the atmosphere at a high speed of more than 70 to 80 kilometers per second. If the body catches up from behind, it will enter the atmosphere at a speed of more than ten kilometers per second. Small meteors and comets often hit the earth. According to statistics, 24 million meteors enter the earth's atmosphere every day and night. On the night of the meteor shower in November 1833, hundreds of billions of meteors bombarded the earth. The ratio of the number of meteors intercepted by the earth to the number of meteors passing by the earth was extremely small. The density of meteor material in the interstellar space around the earth is about 10-23g/cm3-10-21g/cm3. According to statistics, the weight of cosmic dust rain falling on the earth is 90 tons per year, and the weight of high-speed meteor material falling on the ground every day is 10 tons. tons, the weight of low-speed meteorite material is 400 tons. If the average number of meteorites arriving on the surface every day and night reaches 10 tons, then counting more than 2 billion years ago (as now), there will be as much as one ton per square kilometer, nearly 10 centimeters thick. It is said that the soil in the garden is full of meteorite, but most of it is burned out due to the barrier effect of the atmosphere. Meteoroids rub and collide with atmospheric molecules, ionizing the air and heating it to hundreds, thousands or even tens of thousands of degrees. Under the action of high-temperature airflow, meteoroids burn, glow, and vaporize. Because the meteoroid telemotion process is gradual It burns, leaving traces of ionized air along the way, and part of it remains and falls to the surface to become meteorites. If meteorites explode in the air and then splash down like raindrops, it is called meteorite rain. Meteoroids begin to burn and glow at an altitude of 110-130 kilometers above the ground, and are basically burned out at an altitude of 80 kilometers. However, a few meteoroids continue to burn until they are 10-20 kilometers above the ground. At this time, due to the decrease in altitude, The density of the atmosphere increases, the resistance increases, and the falling speed slows down. At this time, a molten shell about one centimeter thick is formed on the surface of the meteoroid. Because it is in a high-pressure environment, the molten shell often appears as a groove-like air mark pressed in like a finger. According to statistics, the number of meteorites falling to the earth every year is <1kg19000±, 1kg4100±, 10kg830±. However, most meteorites fall into oceans and desert areas. There are very few meteorites known and collected by people. They are very few and rough. According to statistics, about 500 meteorites hit the earth every year and only 20 can be found, so they are rare and precious. These extraterrestrial visitors have very important research value. Due to their peculiar shape and origin from the universe, they add a sense of mystery and have become people's collections and ornaments. Meteorites have become an important category of ornamental stones. There are currently more than 10,000 meteorites collected on the earth, most of which are stony meteorites (meteorites for short), followed by iron meteorites and stony iron meteorites. Type I carbonaceous chondrites only account for about 0.6%, but they It is of valuable significance to understand the abundance of elements in the universe, a large amount of ammonia, nucleic acids, fatty acids, 11 kinds of amino acids and other organic compounds, and to understand the origin of life. Meteors and meteorites cannot be completely equated with each other. From an astronomical point of view, meteors are some small interstellar materials, generally ranging from a few millimeters to more than ten millimeters in size. They are generally believed to be the remnants of comets. Meteorites may be fragments of asteroid collisions, ranging from hundreds of grams to large ones up to hundreds of tons. There are also differences in the probability of appearance time. Meteors mostly appear at midnight from July to September (autumn), and meteorites appear from May to June. Meteorite categories Meteorites are divided into categories based on structure, structure, and silicate content. There are three categories: iron meteorites, stony iron meteorites, and stony meteorites (meteorites). According to the different minerals that appear, they are further subdivided into different names.

1. Iron meteorites (iron meteorites) account for 6% of the total meteorites, composed of 91% metallic iron and 8% nickel, containing Co, P, Si, S, Cu, and C. Density

is about 8-8.5g/cm3. Iron meteorites are subdivided into four types: harzburgite, octahedron, nickel-poor breccia porphyry, and nickel-rich breccia porphyry. They are transitional in composition and can be gradually formed by slow cooling of the same iron-nickel melt.