Chinese scientists discovered the world's first alpine meteorite crater! Why are there no traces of meteorites in the crater?

According to Xinhua News Agency and other media reports, Chen Ming, a researcher at the Beijing High Pressure Science Research Center, and his team have made a major breakthrough in the study of planetary impact structures, discovering a peculiar meteorite crater, the Baijifeng meteorite crater, in Tonghua City, Jilin Province. On September 5, 2023, the results were published in the English academic journal "Matter and Radiation under Extreme Conditions".

▲The picture shows the Baijifeng crater taken by a drone

(Photo provided by the research team)

Meteorite impact crater, literally translated as "meteorite impact crater", there is currently an international view that "meteorite" should be removed, because the formation of "meteorite crater" is not necessarily caused by the impact of meteorites or asteroids, but may also be caused by comets, that is, dust and ice. In general, meteorite craters on Earth are ring-shaped pits or ring-shaped geological structures formed by the impact of small extraterrestrial bodies on the Earth's surface.

Although there are many famous meteorite craters in the world, such as the Barringer Crater in Arizona, USA, and the Wolf Creek Crater in Australia, some of which have become world-renowned tourist attractions, no researchers have discovered meteorite craters on high mountains before. The discovery of the Baijifeng crater caused a sensation because it is the impact structure with the largest vertical height difference on the surface known on Earth, and it is also the first meteorite crater located on a high mountain. This provides a new research object for exploring the impact crater formation mechanism and effect of special landforms.

According to reports, the newly discovered meteorite crater is located on the top of a mountain in Baijifeng National Forest Park in Tonghua City. It has a diameter of 1,400 meters. The height difference between the highest point on the rim of the crater and the lowest point in the center of the crater is more than 400 meters. It is in the shape of a cirque, like a huge funnel hanging on the mountain, magnificent and spectacular. Baijifeng National Forest Park is famous for the large number of "sky stones" covering the top of Baijifeng Mountain. Large pieces of rock fragments are piled up on the top of the mountain and the hillside, forming a stone waterfall. However, the cause of these "sky stones" has always been an unsolved mystery in the past.

▲The picture shows the impact rock fragments and the evidence of impact metamorphism

(Photo provided by the research team)

When an asteroid hits the flat surface of the Earth, a bowl-shaped pit is formed. However, when an asteroid falls on a special terrain on the Earth's surface, the propagation pattern and mechanism of the shock wave at the explosion point will change with the terrain (such as the direction of the mountain range). The study found that about tens of thousands of years ago, an asteroid with a diameter of tens of meters hit the top of Baijifeng Mountain at cosmic speed, causing a violent explosion and rock ejection in the target area, forming a huge cirque-shaped impact crater, shaping two new peaks, "Front Baiji" and "Back Baiji", and changing the original shape of the mountain.

Chen Ming introduced: "Baijifeng Mountain is mainly composed of bedrock materials such as Proterozoic sedimentary rocks and Jurassic granite. The stone waterfalls distributed on the top and hillside are the accumulation of sandstone, granite and other rock fragments ejected from the crater to the edge of the crater when the asteroid impact occurred. This discovery has solved the mystery of the formation of Baijifeng Tianshi. On Earth, it is rare for a large-scale meteorite crater to be located on the top of a high mountain as a whole. "This new discovery has enriched mankind's understanding of the history of planetary collisions and provided a new perspective for exploring the impact cratering mechanism of special topography and landforms and the impact metamorphic effect of materials.

In addition, when Chen Ming was interviewed by the Wanxiang Yue Xiaoxiang Kuaipao team earlier, he also answered questions such as "Are there meteorites in the craters?", "Why are there so many craters on the moon, but so few on Earth?", and "What is the economic significance of studying meteorite craters?" The following is the original interview text.

Are there definitely meteorites in craters?

There are two English names for meteorite crater in use internationally. One is a direct translation of "Meteorite impact crater", but now there is a concept that removes the "Meteorite" because the formation of "meteorite crater" is not necessarily caused by the impact of meteorites or asteroids, but may also be caused by comets, that is, dust and ice. So now the concept of meteorite crater is called impact crater in international scientific terms, which is "impact crater". In the last century, they talked about this meteorite crater and called it Meteorite crater. There is no problem in concept, but people who don't know much about this field will misunderstand and think that the meteorite crater must be full of meteorites.

In fact, it cannot be said that there are no meteorites in the crater, because in general, it is formed by the impact of meteorites, but we need to look at the energy of the impact. If a 30-40 meter asteroid hits the earth at cosmic speed, it can form a crater of about 1.2 kilometers, but the energy of this impact is released in an instant, which is equivalent to the explosion of 500 to 600 atomic bombs. Imagine: if an atomic bomb explodes in a place, can we find the shrapnel? Can we say that the material of the shrapnel does not exist? (The related material) definitely exists, but we can't find the shrapnel. Because the temperature of the impact core exceeds tens of thousands of degrees, and the pressure is also very high, it will vaporize at the moment of explosion.

Therefore, not all pits formed by meteorites falling on the surface are meteorite craters. There is a very important scientific concept about meteorite craters, which is that they must explode. Only pits formed by impact and explosion are meteorite craters in the strict scientific sense.

Why are there so many craters on the moon, but so few on Earth?

There are so many overlapping craters on the surface of the moon. Theoretically, the number of craters and the density per unit area on Earth are the same as those on the moon, because we belong to the same Earth-Moon system. The frequency of strong impacts that the Earth-Moon system has experienced in history should be similar. However, there are now 300,000 meteorites larger than 1 kilometer on the moon, but so far there are only 200 on our Earth. Where did the meteorites go on our Earth?

In fact, this is because since the formation of the earth, strong geological activities have caused plate tectonic movements, mountain building movements, volcanic eruptions, glacial movements, etc. on the earth's surface. In addition, there are the common weathering and erosion phenomena and sedimentation and burial of depressions. These can cause the meteorite craters formed on the earth's surface to be damaged, eroded, or even buried. Because of this, the number of meteorite craters preserved on the earth's surface is relatively scarce.

What is the significance of studying meteorite craters?

When we are preparing to explore the moon, Mars, and other planets in the future, we always need to have a full understanding of the geological phenomena on the surface of these planets. We know that at present, there are many technical issues involved in sending astronauts to the moon, and only a few can go there. Therefore, we are still subject to great limitations in understanding the topography, landforms, and geological structures of extraterrestrial planets. Of course, we can now achieve this through remote sensing technology, but if we want to understand the geological phenomena of a region, the evolutionary history of a planet, etc., we still need to have physical objects to study in the end. Therefore, we are now sending people to the moon, and the astronauts have to bring back samples. However, the samples returned by the Chang'e program are very few, only tens of milligrams, hundreds of milligrams, or thousands of milligrams.

In fact, we know that the causes of the craters on the moon and on Earth are the same, and the causes of the craters seen on Mars are also the same, because they are all a big family. If we can find craters on Earth and study their impact effects, then our samples will not be in the order of milligrams, but tons, tens of thousands, or hundreds of thousands of tons. We can study craters on a larger scale, which will enrich our understanding of the formation and evolution history of the Earth and extraterrestrial planets, which is very important. The study of craters on Earth can help or promote our exploration of extraterrestrial planets, but in fact, the significance of studying craters on Earth is far more than this.

We also need to consider the economic significance of studying meteorite craters. For example, impact is a geological process with extremely high temperature and pressure, which can create certain special mineral resources. For example, the world's largest gold deposit is in a meteorite crater; a large part of the world's oil and oil and gas are produced in meteorite craters; and the world's largest nickel deposit is in a meteorite crater; the largest diamond deposit is in a meteorite crater, as well as clay mines, etc. All this information needs to be obtained through studying meteorite craters.

So in general, meteorite crater research is an interdisciplinary science that we in China cannot lack.