I am the wind to the clouds, and today I want to talk about the great mystery of the small meteorite. I'm going to talk about meteorites from the following three aspects. The first one is to talk about what a meteorite is and what is the definition of a meteorite. The second part will share some practical tips. Let's take a look at whether a stone is an ordinary stone on Earth or a meteorite from outer space. And then what kind of impact will be there when an asteroid of different sizes hits the Earth? Okay, let's start with the first part, have you all seen a starry sky like this? I remember when I was a child, I really saw such a starry sky, in the summer, it was very hot in the countryside, there was no air conditioner and no electric fan, what should I do if I couldn't sleep when it was hot at night? We had a way to take the mat to the roof and cool off. I remember at that time, the production team still shared melons to eat, and then I would lie on the mat on the roof, cross Erlang's legs, while eating melons, while enjoying such a beautiful night sky, one by one stars, really just like the book said, like diamonds inlaid on the velvet curtain, very beautiful, when you are lucky, you can occasionally see meteors across the night sky, how are meteors formed? Meteors are dust particles from outer space that emit light by friction as they pass through the atmosphere. Meteors are relatively small, generally only the size of soybeans or mung beans, so they can't form meteorites, and meteorites are associated with the phenomenon of more violent fire meteors. Therefore, a meteor is a phenomenon formed by friction and combustion when a relatively large asteroid enters the Earth's atmosphere. If it happens at night, it will also be very bright at night, and then it will make a rumbling sound. On December 15, 2022, a fireball came unexpectedly. Rowing over the Danxi River in Jinhua, Zhejiang, many car dashcams have been photographed. So everyone must be curious, what did the meteorite fall from? Let's start with this picture, in the middle of our picture, this one has a red fireball, which is our sun, the only star in our solar system. The Sun is bounded outward by the four planets Mercury, Venus, Earth, and Mars, or the inland planets, and further out are the two gas giants of Jupiter and Saturn, followed by Uranus and Neptune. These two ice giants, together they make up the eight planets in our carbon system. If we look at this asteroid belt between Mars and Jupiter, there are many stones, how should the asteroid belt be understood? Let's take an analogy, if our solar system is compared to an edifice, then the sun is undoubtedly the main part of this edifice. Because the mass of the sun accounts for 99.8 percent of the entire mass of the solar system. The eight planets are part of the edifice in our solar system, and the asteroids are the bricks and sand left over after the edifice is built, so the asteroid will be known as the cornerstone of the formation of our solar system, or the fossil that evolved from our solar system. Of the meteorites collected so far, 99.8 percent of them are from asteroids, and only 0.2 percent are from the Moon and Mars. There are no meteorites of Mercury and Venus yet, why? Because Mercury is too close to the Sun, if a rock sputters out, it will also be affected by the strong influence of the Sun's gravity and change its orbit. Venus, on the other hand, has a very thick atmosphere, so it is difficult for the sputtered rocks to escape the constraints of its atmosphere. So how exactly should meteorites be defined? We say that meteorites are debris from the collision between heaven and earth, roaming in space. Then, when he roamed near the Earth, he was captured by the Earth's gravitational field, and then entered the Earth's atmosphere to rub and burn, glow and heat, forming the phenomenon we see as a fire meteor. After falling to the earth, this meteoroid did not burn up, so we call it a meteorite. The Han Dynasty historian Sima Qian has a few words to accurately give the definition of meteorite, and when the star falls to the ground, the stone is also. As the name suggests, it means that stars from outer space fall to the surface of the earth, and then the meteorite is not very accurate. China is the earliest country in the world to record fire meteors, and more than 4,000 years ago recorded an iron meteorite rain that occurred in Xia County, Shaanxi Province. In the local chronicles of the Ming Dynasty, a fire meteor event occurred in Nandan County, Guangxi more than 500 years ago is clearly recorded. Let's take a look at what he wrote. Zhengde Bingzi summer May night, Jingyuan northwest starfall, six zhang long, euphemistic like a dragon and snake, flickering, you see it from the shape, size, sound, brightness and duration of time, multiple angles, angles clearly recorded this time of the fire meteor event. In 1958, some villagers went into the mountains to look for iron ore and accidentally found dozens of such iron meteorites. In fact, our ancestors had learned to develop and utilize meteorites as early as the Shang and Zhou dynasties more than 3,000 years ago. Ah, this is a 14th century BC iron blade copper Yue unearthed from the Shang Dynasty site in Gaocheng, Hebei Province in 1972. The study found that this iron blade is not artificially smelted iron, but comes from iron meteorites. In ancient times, it was a ritual vessel, a symbol of power, status and status. It can be seen that meteorites were very sacred in the minds of the ancients. And not only our ancient Chinese thought so, but in the eyes of this pharaoh in ancient Egypt, he also thought so. More than 3,000 years ago, the tomb of the Egyptian pharaoh Tutankhamun was selected as one of the world's top ten rare tombs. Archaeologists found a special dagger inside his mausoleum, and hey, he wasn't very rusty. Then after research and analysis, it was found that its nickel content is very high, the mass percentage can reach about 12%, and it presents a very unique structure of this Weiss table lamp. Well, based on these two points, scientists confirmed the composition of this dagger, it is a meteorite. Okay, now let's move on to the second part, how do you identify a meteorite? First of all, the first important thing is to look at the appearance. We say that meteorites are formed by the combustion of the atmosphere, so the surface of the meteorite will melt and form a layer of glass. This layer of glass is usually black, but in rare cases it is green, etc. So meteorites are generally like wearing a black coat, which is about a millimeter thick. We call this coat a molten shell. Then there will be this air mark on this crust, which is formed by the interaction between meteorites and the atmosphere. This air mark is like a thumb on the seal, usually the larger the meteorite, the larger the air mark will be. Also, the original molten shell usually cracks, and it cracks in the form of irregular polygons. So, this molten shell gas mark and this crack is a very direct, simple and important evidence for us to judge a meteorite. Okay, let's look at the second one is to see that more than 90% of the meteorites inside are chondrites, and the characteristics of the meteorites of the balls are that they contain large and small chondrites inside. These pellets are about a millimeter in size. So why is this chondrite globular in shape? Because they are formed in the solar nebula, after high temperature melting, and then cooling and crystallization without gravity, they are spherical. Chondrites usually contain metals inside, so for a chondrite meteorite in a galaxy, you can also see shiny metal. For this meteorite that is not fresh, the metal will rust, and we will look rusty. So based on these, we can also judge that this is a meteorite. Then the third is weighing, we say that the density of ordinary stones on the earth is about 2.5 to 3 grams per cubic centimeter. And the density of our iron meteorites can reach eight, so the iron meteorites are equivalent to three times the size of the earth's rocks. And the density of stony meteorites is equivalent to 1.5 times that of Earth's rocks of the same size. Therefore, when we hold a meteorite in our hands, we can usually feel that it is heavier than ordinary stones. So the fourth one is pickled, uh, there is a type of meteorite called iron meteorite, so how should we understand iron meteorite? If we compare its small parent body to a hard-boiled egg, then the iron meteorite comes from this yolk, which means that it comes from this sample from the deepest part of the asteroid, because it is mainly composed of iron, so we call it an iron meteorite. How to pickle, we first cut it into a smooth plane, and then use a relatively fine acid, such as 10% nitric acid and 90% alcohol to mix it for pickling. It's interesting that before you pickle it, it's like a flat piece of smooth stainless steel. But after you pickle it, you will show such criss-crossing stripes. It turns out that this stripe is made up of two minerals, ironstone and nickel-grained stone. They have different degrees of corrosion resistance to acid, and the lines come out after pickling. We also have a name for this stripe called the Vesteden structure. The Vesteden structure is formed by the slow cooling of the interior of the asteroid parent over millions of years. It's something that humans can't imitate for the time being. The chondrites we just talked about, the density is heavy, and the Weiss lamp structure is used to identify asteroid meteorites. So how to identify meteorites from the Moon and Mars? Because the Moon and Mars are relatively large, the rocks on the Moon and Mars are relatively similar to the rocks on our Earth, so it is not easy to judge so much. In 1981, the United States found the first lunar meteorite at the South Pole. When they brought this lunar meteorite back, they compared it with the samples they had returned from the moon in the seventies, and it soon became clear that it was the same. Then it was confirmed that the meteorite came from the Moon. As for Mars, we humans have not returned samples from Mars so far, and we can't compare them. Martian meteorites are formed when an asteroid hits the surface of Mars, splatters out the rocks on the surface of Mars, and then floats into space and is captured by the Earth's gravity. Because Mars is a relatively large planet, Mars has a relatively large escape velocity, five kilometers per second. So you are going to dig it out, then you have to overcome its escape velocity. Then the energy required for the impact is relatively high. So this impact process will melt part of the excavated rock to form glass. Then this glass includes Martian nitrogen that encapsulates a part. Therefore, when scientists analyzed the gas wrapped in this sample and compared it with the Martian atmosphere detected by the Viking Mars rover, they found that they matched very well on a one-to-one line, and finally confirmed that its ** came from Mars, so the process was very difficult. So let's look at the second point, which is oxygen isotopes. Oxygen isotopes For meteorites, this sample is different, it has different oxygen isotopes. For example, if we look at the Martian meteorite, its oxygen isotopes are distributed almost along such a Martian mass shunt line, which is different from that of the Earth, the Moon and the asteroids. So by analyzing the oxygen isotope, we can also determine it's **. Then the third is to look at age, we say that people have a lifespan, a planet, and a lifespan, how do you look at the lifespan of a planet? If we compare magma to the blood of a planet, then the time of the last blood flow on the planet represents the end of the geological life of the planet. We now see that the earth is large, and the energy plants are still volcanic. So we say that our Earth is alive, but what about Mars, which is about half the size of Earth. Studies have shown that its volcanic activity stopped in 200 million years, and that the moon is half the size of Mars. China's Chang'e-5 sample study shows that the moon stopped volcanic activity 21 years ago, and the asteroid is even smaller. The largest asteroid has a radius of only a few hundred kilometers. So, it is generally believed that the asteroid died more than four billion years ago. So when you analyze a can of sample, and it's very young, only a few hundred million years old, then you probably suspect that it should come from a relatively large planet like Mars. The fourth point is to analyze the mineral composition of the meteorite itself. We say that rocks are made up of minerals, and minerals are made up of elements. So scientists have found that Mars, Vesta, Earth, and the Moon, these four celestial bodies are different in the ratio of iron and manganese elements in pyroxene. So we can also see their ** by analyzing the ratio of this element of minerals. Have you found that the identification of Martian meteorites is very complicated, and it requires professional knowledge and professional equipment to complete. Okay, let's summarize it now. We said that among the meteorites collected now, 99.8% of the meteorites are meteorites from asteroids, and the rest are from the moon or Mars.
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