After reading this article, you can also pick up meteorites in the wild!

Although I have been doing meteorite research,

But that was also my first time,

See with your own eyes the stars falling to the earth.

If we look up at the sky on a clear night, we can sometimes see shooting stars. When there is a meteor shower, young people usually like to compete to see who can see more shooting stars.

▲2001 Leonid meteor shower

Actually, there is no relationship between meteors and meteorites. Meteors are tiny dust particles in the universe. When they pass through the Earth's atmosphere at high speed, they emit light and heat due to friction. Therefore, most meteors are burned, and only a small part may remain. If you want to find the dust of these meteors, it is best to go outside the atmosphere, such as collecting it on the space station.

▲Fire meteor

Meteorites are related to fireballs. Fireballs are asteroids that enter the atmosphere. They hit the Earth at a speed of more than 10 kilometers or even 20 kilometers per second. When passing through the Earth's atmosphere, they form a fireball due to high-speed friction. Because fireballs are often relatively large, the unburned parts fall to the ground and are picked up by us. This is what we call meteorites.

How to distinguish real and fake meteorites?

From the falling process of meteorites, we can know that meteorites have a characteristic that distinguishes them from Earth rocks: during the high-temperature combustion process, the surface melts and quickly cools down to form a layer of glass, which we call a fusion crust.

▲Real meteorite

The thickness of this layer of glass on the surface is very thin, only about one millimeter, which is completely different from the inside of the meteorite, so it is easy to distinguish. In addition, this layer of glass often cracks into polygons, which will become very obvious after a long time.

We often receive so-called meteorites from enthusiasts, most of which are fake. Although some samples have "melt crust" on the surface, most of them are actually the paint skin of some desert stones, which is continuous with the internal components. In addition, some are black iron ore, which is not a real meteorite either.

The fusion crust is the most important feature of meteorites, which is essentially a layer of glass on the surface. Most fusion crusts are black, but a very small number of them are very special and present a beautiful green color like jade.

About 90% of meteorites contain metal particles. We know that metal is easy to rust, so the internal composition of meteorites without the fusion crust often appears as a rusty brown with varying shades. This is also an important feature for identifying most meteorites.

▲Chondrite

In addition to metal components, meteorites also contain some very small, round stone spheres, which are formed by melting without gravity, so they are very round. We call them chondrules, and meteorites with chondrules are called chondrites.

In addition, there are some meteorites that are composed of metals that you may be more familiar with, called iron meteorites. In front of the Xinjiang Geological and Mineral Museum in Urumqi, there is the largest iron meteorite in my country - the Xinjiang Iron Meteorite.

▲Xinjiang iron meteorite

If a piece of iron meteorite is cut and polished, and then the surface is etched with a very dilute acid, an uneven pattern will be produced.

▲Weisteden structure: 2 types of iron-nickel alloys

This pattern is actually due to the different nickel content in two different iron-nickel alloys, so their corrosion resistance is different, which will appear. It takes millions of years to slowly cool down to form, so there is no way to imitate it in the laboratory.

Have you ever seen a meteorite fall?

I just talked about fireballs. If a fireball is picked up by people immediately after it falls to the ground, we call it a witnessed landing meteorite.

The picture above shows Academician Ouyang Ziyuan leading researchers to inspect the most famous stone meteorite in my country in Jilin. It is also the largest stone meteorite shower in the world, with the largest piece weighing nearly 1.8 tons.

Witnessed meteorites are very rare. Because they were picked up right after they fell, they are very fresh. There are some very famous witnessed meteorites in my country, including the Qingzhen meteorite that fell in Guizhou Province in 1976, the Ningqiang meteorite that fell in Shaanxi Province in 1983, and the Suizhou meteorite and Yanzhuang meteorite containing high-pressure minerals. At present, there are only about 67 named witnessed meteorites picked up in my country, which is still very few.

Generally speaking, meteorites fall in sparsely populated areas, but in a few cases they can hit people, cars, or even homes.

In 2008, a meteorite fell in a small village called Xinglongquan, about 3km away from the Eastern Qing Tombs in Beijing. Not long after the hostess of the house left the sofa, a meteorite smashed through the roof, hit the sofa, and finally bounced onto the bed. The meteorite also left scratches on the mirror and broke into several pieces, weighing about 3kg in total. This is a very rare event, and fortunately, not only did no one get hurt, but it also made a fortune.

▲The Chelyabinsk meteorite in Russia

You may remember a piece of news. In 2013, a very famous Chelyabinsk meteor shower occurred in Russia. When the meteorite hit, the largest piece of meteorite directly hit the lake, and the fragments were scattered over a large area. The total weight of the collected samples exceeded 1 ton. The energy of the meteorite impact was very large, and the strong shock wave destroyed many buildings and indirectly caused more than 1,000 injuries.

Although an asteroid hitting the Earth is a very low probability event, it could be a disaster. Simulation calculations show that if the diameter of an asteroid exceeds 140 meters, then the impact of a meteorite will bring disaster to a region. If the diameter of an asteroid is more than one kilometer, it may cause a global disaster.

Let’s go to Antarctica to pick up stars!

We have seen very few meteorites falling on Earth, and we have picked up about 1,300 of them. In fact, there are more than 60,000 named meteorites, and we don't know when most of them fell.

So, where is a good place to pick up meteorites? Antarctica!

As we all know, Antarctica not only has a harsh climate, but also has many very dangerous places, so our inland team needs to see them off and drink farewell wine before going to the inland Antarctic for scientific research.

▲The departure ceremony of the 22nd Antarctic Expedition Inland Team (2005.12.23)

We went to Grove Mountain in Antarctica, which is more than 400 kilometers away from Zhongshan Station. It took us eight days to reach the camp on the last day of 2005. When we first arrived at the camp, although the 11 people in our team were doing various field surveys, the first thing everyone thought of was to look for stars.

The first person to find the meteorite was mechanic Xu Xiaxing, who immediately shouted, "Teacher Lin, Teacher Lin, come here quickly." Although I have been doing meteorite research, it was also the first time I saw a star fall to the earth with my own eyes, so I was quite excited at the time.

The next day was New Year's Day 2006. We did nothing else and put aside our research papers. The first thing we did was to look for meteorites. In the end, each of us found a meteorite, and I personally found the first meteorite, fulfilling my dream of looking for meteorites in Antarctica.

In the picture above, the surface of the Grove Mountain area in Antarctica is a blue-fluorescent ice surface, and part of the surface is covered with snow. The meteorite is very conspicuous against this background, so it is easy to find.

Because there are many rocks from Earth in the ice zone, it is difficult to find them. However, if you look at the fusion crust of the meteorite, it is still easy to identify it.

On January 16, 2006, many of us went to do our own research, and only four of us went to look for meteorites. We found more than 600 meteorites in total, with a total weight of about 19.2 kilograms, which is very rare.

▲Yellow and red symbols indicate where the meteorite was found

Green symbols indicate campsite locations

The local satellite image shows that the ice flows from the right to the left and is blocked by the mountains, while the meteorites are mostly distributed downstream of the mountains. The green symbol indicates our campsite. After we finish working in one place, we move to the next place. On the way to Camp 7, we sat in the car and stared at the ice surface. When we see a small black dot and it doesn't change, it may not be a shadow. So I asked the captain to stop the car, ran over to take a look, and sure enough, I found a very beautiful meteorite, very fresh, weighing 1.5 kilograms.

There are many difficulties you will encounter in Antarctica, one of which is albino weather, when the sky and the earth are covered in white. Not only can you not see anything, but you will also lose your sense of direction.

The most important and dangerous thing is the ice cracks, which are actually invisible because they are covered by snow. They only appear when a car runs over them. If the ice cracks are large, the car and the people will fall into them and will definitely not be able to get back out. This is very dangerous. This time, because of the experienced mechanics Xu Xiaxing and Li Jinyan, and the team leader Ju Yitai, it was relatively safe.

The first time we went to Grove Mountain, it was very dangerous. There were only 5 people and 1 car, and our team leader was researcher Liu Xiaohan. It was more difficult and dangerous than this time.

The main problem of living in Antarctica was that there were no vegetables to eat. Pork, beef, and mutton were all frozen hard and needed to be chopped with an axe. We only brought one cabbage with us, which we kept for making dumplings during the Spring Festival.

During the 58 days in the Antarctic interior, everyone completed their field research and picked up 5,354 meteorites. We were all very happy and felt much more relaxed on the return journey.

You may ask, do all meteorites fall to Antarctica? There are many meteorites there, so we go to Antarctica to look for them? Actually, no. The probability of meteorites falling anywhere on the earth is the same. There are probably a few meteorites in an area of ​​10,000 square kilometers per year, or even fewer.

There are two reasons why there are more meteorites in Antarctica. First, Antarctica is very cold and very dry. Meteorites are very afraid of water and can only be preserved for millions of years in a very dry environment. Second, meteorites flow with the ice and stop in places blocked by mountains. Strong winds blow away the ice, and meteorites remain. Therefore, Antarctica is the best place to find meteorites.

In addition to Antarctica, another good place to find meteorites is the desert. Because the desert is very dry, meteorites can be preserved in the desert for hundreds of thousands of years. However, there is no ice in the desert to transport meteorites, so compared to Antarctica, meteorites will not be concentrated in a certain place in the desert.

There are large areas of desert in northwest my country, especially in Xinjiang. In recent years, many meteorites have been discovered, and 251 Chinese desert meteorites have been named.

These meteorites are very precious and rare things. If we find a meteorite, we need to pay attention to some things.

First, take some clear photos of the meteorite from multiple angles to record the meteorite's appearance when it falls to the ground. Then use GPS to record the geographic coordinates, and also record the surrounding landforms. Pay special attention to storing the meteorite in dry conditions and keeping it sealed, because meteorites are afraid of water. Many people may use magnets to attract meteorites, but it is best not to do so, because this will change the magnetism of the meteorite. If you are sure it is a meteorite, don't do this.

Another important point is to contact a professional organization as soon as possible to help you classify, identify and name it. This requires providing a sample of no less than 20 grams, or 20% of the weight, as a specimen of the meteorite.

Unlike rocks on Earth, each meteorite has a name, and research results on unnamed meteorites cannot be published. We generally name meteorites after the place where they were discovered. If so many meteorites are found in the Grove Mountains area of ​​Antarctica, we would name them after the place name plus the time, for example, GRV stands for Grove Mountains, 02 stands for 2002, and 0090 is its number.

Where do meteorites come from?

You may ask, where do all these meteorites come from? The more than 60,000 meteorites found around the world can be roughly divided into three sources: asteroids, the moon, and Mars.

Asteroids are widely distributed throughout the solar system, mostly in the asteroid belt between Jupiter and Mars. Those that fall to Earth are near-Earth asteroids, whose orbits intersect with Earth's orbit.

We don't know the orbits of most asteroids, but for a few asteroids, we can set up cameras at three locations to shoot fireballs in the sky, use triangulation to calculate their orbits, and then find meteorites based on the calculated positions. With this method, a meteorite was found in Neuschwanstein Castle, a very famous castle in Germany. The left picture shows the orbits of some meteorites we know, but they are very few.

There is a type of meteorite that is even more special. In recent years, there have often been news reports saying when a meteorite with a certain number might intersect the earth at a close range.

In 2008, an observatory observed an asteroid and calculated that its orbit would not be close to the Earth, but would directly hit the Earth. 20 hours later, the asteroid did hit the Earth, and a meteorite was found at the predicted location.

▲The red dot indicates the location where the meteorite was successfully found within the predicted range

These meteorites are very special and include many different types. One type is ureilite, which contains diamonds and is so hard that it takes a day to cut off a small piece the size of a thumb.

In addition, there are lunar meteorites found in the African desert and my country's second Martian meteorite found in Grove Mountain in 2002.

What is the point of finding so many meteorites? First of all, for most people, this is a very rare gift from heaven, it is really a star in the sky. A small number of meteorites are very beautiful in appearance, so they are also collections of strange stone lovers.

Because meteorites are very rare, there is a certain market, but there are no clear laws and regulations in this regard. It is easy to find the transaction prices of some meteorites on the Internet. The price per gram ranges from a few dollars to one or two thousand dollars per gram, which is very different. This mainly depends on what type it is, whether it is very rare, and whether it has great scientific value.

▲Fukang olive meteorite

The most important value of meteorites lies in scientific research. They tell us how the solar system was formed, the evolutionary history of the planets, etc. Different types of meteorites tell different stories.

Most meteorites come from asteroids, which we call fossils of the solar system. Through them, we can understand how the solar system evolved from a nebula disk of dust and gas to the eight planets.

In addition to scientific research, there may be a risk of an asteroid hitting the Earth, so we also need to monitor, warn and defend against asteroid impacts through research.

In the future we will go into space, and we cannot bring everything from Earth, so asteroids are also very important space resources in the future.

Lunar meteorites are another story. Currently, our lunar samples are mainly collected and brought back to Earth by the Apollo missions, with a total of 382 kilograms of lunar samples collected in six missions. In addition, the former Soviet Union collected 300 grams of samples from the moon in three missions.

More than 400 lunar meteorites have been found, with a total weight of more than 600 kilograms, which exceeds the total weight of lunar samples brought back by Apollo.

▲The first lunar meteorite identified in human history

The first lunar meteorite (ALH81005) was found in Antarctica in 1981. After bringing the meteorite back, scientists studying lunar geology found that it was exactly the same as the lunar rock samples collected by Apollo, and soon determined that it was a lunar meteorite.

In fact, Japanese scientists found three lunar meteorites from Antarctica earlier, but they did not recognize them, so they lost the first opportunity to discover lunar meteorites.

▲Distribution of iron oxide content on the front and back of the moon

(Black dots indicate Apollo and Luna landing sites)

By comparing the distribution of iron oxide content on the front and back sides of the moon, we can see that the composition of the moon is uneven. The lunar samples collected by Apollo and the former Soviet Union were all in a very small area on the front side of the moon. The composition of the moon on the back side of the moon and other areas needs to be further analyzed and studied through lunar meteorites.

my country's Chang'e 3 landed on the front side of the moon, and Chang'e 4 was the first in human history to land on the back side of the moon, and it landed in a large and deep impact basin.

▲The oldest and largest impact crater, 13 kilometers deep,

Opening a window into the deep interior of the Moon

Last year, there were three Mars launch missions, namely the United States' Perseverance, the United Arab Emirates' Hope, and my country's Tianwen-1. The three Mars probes are all for remote sensing and will not bring back Martian samples. At present, Martian meteorites are the only Martian rock samples we can get. In fact, Martian meteorites were discovered very early and confirmed very late. The first Martian meteorite fell in France in 1815. At that time, it was only thought that this meteorite was very special. Because there were no Martian samples to compare, it was not certain that it came from Mars.

We can determine the age of rocks by measuring the radioactive isotope composition of the rocks (such as the decay of U isotopes). For example, the age of rocks formed by volcanic eruptions is zero, the age of asteroid meteorites is 4.5 billion years, and the age of lunar rocks is between 3 billion and 4 billion years.

The age of these Martian meteorites is 1.3 billion years, or even younger than 200 million years. This shows that they came from a celestial body larger than the moon, but based on this alone, it cannot be determined that it came from Mars.

After cutting open this Martian meteorite, glassy black spots were found inside. This is glass formed under high temperature conditions when the asteroid hit Mars, and Martian gas is contained in the glass. Its analysis results are exactly the same as those of the Viking analysis of the Martian atmosphere in 1976, which proves that this meteorite is indeed from Mars.

There are 268 Martian meteorites discovered so far, weighing more than 200 kilograms. Our understanding of Mars depends largely on the study of Martian meteorites.

Why do people care so much about Mars? Many people believe that there is life on Mars. In 1996, NASA scientists claimed to have found evidence of life in the ALH 84001 Martian meteorite, sparking controversy. Now it is generally believed that the previous evidence was either contamination from the Earth or artificially produced during the sample preparation process.

▲Mars meteorites: Debate on the remains of life on Mars

In any case, exploration of Mars' morphology and other aspects has found that there should have been rivers, lakes and even ancient oceans on Mars, and there is also some methane in the Martian atmosphere, which means that Mars at least once had the basic conditions for the existence of life. The ongoing Mars exploration program and future missions still regard the detection of life as the most important goal.

Another way to study life on Mars is to study environmental changes on Mars, that is, to determine whether it is habitable. One idea is to conduct relevant research through Martian meteorites.

After the magma of the Martian meteorite cooled, the rocks interacted with the groundwater, thus recording the information of the Martian groundwater at that time. Here we are concerned with the hydrogen isotope composition of water, that is, the D/H ratio. This ratio can distinguish the water on Mars from the water on Earth, which is equivalent to the fingerprint of water.

We say that there was water on Mars in the past, but there is no flowing water on the surface now, so some of the water has escaped into space. The more water that escapes, the heavier the remaining water is, that is, the greater the D/H ratio. Therefore, it is important to measure the D/H ratio of groundwater on Mars.

We cut the Martian meteorite into pieces, ground it into slices and studied it, and found that there were two places with relatively high water content: one was magma trapped in minerals, that is, glassy inclusions, and the other was the hydrous mineral apatite.

Since the samples to be analyzed are very small, we used the nano-ion probe equipment of the Institute of Geology and Geophysics, Chinese Academy of Sciences.

This instrument will form a very fine primary ion beam as small as 50 nanometers to bombard the surface of the sample. The secondary ions that are bombarded will be deflected when passing through a magnetic field. The smaller the mass, the greater the deflection, so ions of different masses can be separated, and then the receiver will record the strength of the information separately, so that the water content and D/H ratio of the sample can be obtained.

The results of the apatite experiment show that the water content in the Martian magma is very low, about one-tenth of that on Earth, which means that Mars is very dry. The glass inclusions reflect the mixture of water inside Mars and water on the surface of Mars. Based on this, we know that the hydrogen isotope composition of the Martian surface water is very heavy, about 7 times heavier than the ocean water on Earth, indicating that a lot of water has escaped from Mars.

We believe that there was flowing water on the surface of Mars about 3 billion years ago. As Mars gradually cooled, some of the water ran away, and some of the water became underground glaciers and permafrost. If there was a magma eruption 200 million years ago, the heat brought by it could melt the underground permafrost and glaciers to form water, which could provide an environment conducive to the existence of life.

From searching for scattered stars, to analyzing and studying these stars, to actively exploring various celestial bodies and collecting samples to return to Earth, we can better understand the origin and evolution of the Earth and the entire solar system. With the rapid advancement of technology, humans will eventually leave the cradle of the Earth and discover new continents.

Science Communication Research Center of Chinese Academy of Sciences

Editor | Cao Ruiyue

Proofreading | Li Sijin Li Chun

Audit | He Yong