How to monitor near-Earth asteroids? See China's Sky Eye and Compound Eye

In the solar system where we live, in addition to the eight planets and their satellites, there is a group of uninvited guests who occasionally visit the Earth and even savagely break into the Earth's atmosphere, disintegrate and explode in the atmosphere, and bring powerful shock waves to the creatures on Earth, damaging trees and houses and causing injuries. Under extreme conditions, they will reach the ground, and the powerful impact will cause earthquakes, tsunamis, volcanic eruptions, and even completely change the Earth's climate and environment, as well as large-scale species extinction on Earth. They are near-Earth asteroids.

It is said that 65 million years ago, a near-Earth asteroid with a diameter of about 10 kilometers hit the Gulf of Mexico region of North America, causing a mass extinction of species on Earth. The dinosaurs that had ruled the Earth for 160 million years also withdrew from the Earth's stage after this impact.

65 million years have passed, and these space terrorists have not given up. Just 10 years ago in 2013, a near-Earth asteroid with a diameter of about 18 meters exploded over Russia, with an energy equivalent to about 30 Hiroshima atomic bombs. Fortunately, the airburst height was about 30 kilometers high, and most of the energy was released in the air, but it still caused nearly 1,500 injuries in sparsely populated Russia.

There are millions of near-Earth asteroids with a diameter of only 20 meters around the Earth, and we have not yet discovered where more than 99.9% of these asteroids are. If the small size can reach 50 meters, it is enough to destroy a large city. There are hundreds of thousands of such asteroids around our Earth, and we have not yet discovered more than 95%. Near-Earth asteroids with a diameter of 140 meters can destroy a small or medium-sized country. There are about 30,000 near-Earth asteroids of this size, and we have not yet discovered more than 60%.

Therefore, we cannot take these terrorists in space lightly. Our top priority is to check their household registration and establish a catalog database. Do you know what telescopes scientists use to monitor near-Earth asteroids? Speaking of telescopes, you may think of the Hubble Space Telescope, the Chinese Sky Eye, and even the recently popular Chinese Compound Eye.

The picture comes from Tuchong.com

How do we discover near-Earth asteroids? In fact, the main function of these telescopes is not to discover near-Earth asteroids. Currently, the main equipment for discovering near-Earth asteroids is the optical telescope on Earth. The advantage of optical telescopes is that they have a long detection distance and a large detection field of view. For example, the world's most powerful near-Earth asteroid survey system, the Catalina Sky Survey System in the United States, can detect near-Earth asteroids with an equivalent diameter of 140 meters at about 150 million kilometers. The United States is building a new generation of large comprehensive survey telescopes SST, which can detect near-Earth asteroids with an equivalent diameter of 45 meters at 150 million kilometers. The SST telescope is expected to be officially operational in 2023, and it is expected to discover a large number of small and medium-sized near-Earth asteroids, which will increase the speed at which humans catalog these dangerous elements in space.

After discovering new asteroids, they need to be tracked and measured to determine their precise orbits, three-dimensional shapes, rotations, material composition, structures and other information. This is where radar telescopes come in handy. Radar telescopes have high-precision ranging capabilities, which can greatly improve the accuracy of orbital measurements of asteroids. By analyzing electromagnetic echo data, they can depict the three-dimensional shape of asteroids, surface material composition and other detailed information, which is extremely valuable for understanding the impact hazards of asteroids.

Since asteroids themselves do not emit electromagnetic waves, although the Chinese Sky Eye has a large aperture, it cannot independently complete the tracking and observation of asteroids. The Chinese Compound Eye, which is currently under construction, is a large radar array composed of many small radars. It can actively emit electromagnetic waves to the surface of an asteroid, receive echoes, and detect the physical characteristics of the asteroid surface. In the future, the Chinese Compound Eye may also cooperate with the Chinese Sky Eye, making full use of the active emission capability of the Chinese Compound Eye and the powerful receiving capability of the Chinese Sky Eye to conduct long-distance detection of asteroids. Contribute more Chinese strength to early warning of the risk of near-Earth asteroid impact.

Although radar is good, it is not omnipotent. Radar needs to actively transmit signals to the surface of the asteroid, which requires extremely high pointing accuracy, which requires the measurement data of the optical telescope for guidance. This is why radar can only be used to track asteroids, while optical telescopes are used to conduct wide-area surveys and searches of asteroids.

Although humans have built so many telescopes, our current near-Earth asteroid monitoring and early warning system is far from perfect. Optical telescopes on Earth can only work at night. If an asteroid hits from the direction of the sun, like what happened in Russia 10 years ago, we may not be aware of it. To solve the problem of monitoring and early warning of asteroids from the direction of the sun, we need to put the telescope in a suitable orbit in space, and scientists are working hard to do this.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Li Mingtao

Reviewer: Zhou Binghong (Researcher at the National Space Science Center, Chinese Academy of Sciences)

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.