What should humans do when an asteroid collides with Earth? This is the ultimate survival proposition explored in many science fiction movies. I also watched the movie 'The Wandering Earth', and the artist fully utilized their imagination, but some of the plot still has scientific basis Wu Weiren, academician of the CAE Member and chief designer of the Chinese lunar exploration project, told the Science and Technology Daily reporter during the Xiangshan Science Conference a few days ago. The boundary between science fiction and reality is not strictly guarded. At the beginning of this year, a small asteroid named "2024 YR4" attracted global attention due to the possibility of colliding with Earth. Although it was ultimately confirmed to be a false alarm, exploring near Earth asteroid defense is not an unfounded concern. At the 776th academic symposium of the Xiangshan Science Conference, experts such as Wu Weiren called on China to promote the implementation of the asteroid defense concept and to quickly carry out in orbit disposal demonstration and verification tasks. About 65 million years ago, a small asteroid with a diameter of about 10 kilometers collided violently near the Gulf of Mexico, triggering a global climate disaster and rewriting the history of Earth's biological evolution; In 1908, a small asteroid with a diameter of about 50 meters exploded over the Tunguska River in Siberia, burning more than 2000 square kilometers of forest; In 2013, a small asteroid with a diameter of about 17 meters exploded over Chelyabinsk, Russia, causing nearly 1500 people to be injured in the shock wave... These rare but deadly events warn humanity that the impact of near Earth asteroids on Earth is a potential threat and long-term challenge faced by human society. Wang Chi, an academician of the CAS Member and director of the National Space Science Center of the Chinese Academy of Sciences, said that humans have discovered more than 37000 NEAs. According to the theoretical population model of near Earth asteroids, humans have currently completed the cataloging of over 95% of near Earth asteroids with diameters up to 1000 meters. However, there are still a large number of small and medium-sized near Earth asteroids that have not been cataloged, and once they collide with Earth, they may trigger regional level disasters. The scientific community has identified asteroids with a minimum distance of 0.05 astronomical units (approximately 7.5 million kilometers) from Earth's orbit and a diameter greater than or equal to 140 meters as potential threat asteroids. Currently, more than 2400 such asteroids have been discovered. To prevent problems before they arise, the international community has taken action. In 2014, the International Asteroid Warning Network and the Space Mission Planning Advisory Group were established within the framework of the United Nations Committee on the Peaceful Uses of Outer Space to actively respond to asteroid threats. Countries and regions such as the United States, Russia, and Europe have established specialized agencies to coordinate and organize their own and local asteroid impact risk response efforts. As a major space power, China will not be absent from interstellar protection. The White Paper on China's Aerospace in 2021 proposes to demonstrate the construction of a defense system for near Earth small celestial bodies. At the second International Conference on Deep Space Exploration (Tiandu) held in 2024, China's first near Earth asteroid defense mission plan was released. Kinetic energy impact is the most practical means to deal with the danger of asteroids as extraterrestrial visitors, involving many aspects such as monitoring and early warning, disaster assessment, and in orbit disposal. At the Xiangshan Science Conference, how to dispose of asteroids in orbit has become a hot topic. Wu Weiren introduced that there are three methods for in orbit disposal. One is kinetic energy impact, which causes asteroids to change orbit or break apart through direct impact. This method is suitable for small asteroids with shorter warning times, or large asteroids with longer warning times. The second is nuclear explosion, which is suitable for larger asteroids with shorter warning times. The third is long-term forces, which can cause asteroids to change their orbits through contact or non-contact forces, including gravitational pull, laser ablation, ion beam pull, mass drive, solar pressure, and other methods. Among them, kinetic energy impact technology has high maturity, significant effects, and does not require long-term orbital operations. Kinetic energy impact is currently the most realistic and feasible in orbit disposal method for dealing with small and medium-sized near Earth asteroids, "said Wang Chi. In September 2022, the US "Double Asteroid Alignment Test (DART)" mission successfully completed a demonstration of kinetic energy impact in orbit disposal. The spacecraft collided with the satellite Dimofos of the near Earth binary asteroid system at a speed of 6.1 kilometers per second at a distance of about 11 million kilometers from Earth, shortening its orbital period around its parent star by 33 minutes. Conducting demonstration missions for kinetic energy impact in orbit disposal is also a direction that Chinese scientists are striving towards. Wang Chi suggested that China's first asteroid defense in orbit verification mission could change the orbit of a near Earth asteroid with a diameter of about 30 meters through kinetic energy impact, and comprehensively evaluate the impact effect through joint observation of ground-based and space-based equipment. When it comes to the idea of demonstrating the disposal of kinetic energy impacts in orbit, Wu Weiren proposed 12 words: accurately hit, push, evaluate, and explain clearly. Behind these 12 words, there are a series of scientific and engineering technical questions that urgently need to be answered. How to hit accurately? This requires precise measurement and determination of the target asteroid's orbit and three-dimensional morphology information before impact. Ji Jianghui, a researcher at the Zijinshan Observatory of the Chinese Academy of Sciences, said that space-based monitoring plays an irreplaceable role in this regard. He suggested that by optimizing the ground-based observation station network and coordinating with the space-based satellite network, a near Earth object monitoring and early warning system covering the whole day can be constructed to enhance the ability of asteroid orbit prediction and impact risk assessment. How to push it? This requires studying the impact effects such as crater formation, sputtering, and disintegration, as well as the laws of momentum transfer. Professor Li Jianyang from the Department of Space and Planetary Sciences at the School of Atmospheric Sciences, Sun Yat sen University, analyzed that the stress intensity, friction coefficient, and porosity of the target are the dominant factors affecting the transfer of impact momentum. The overall shape of the target, the terrain of the impact point, the proportion and distribution of rocks, etc. also affect the completion of the impact mission. To achieve maximum momentum transfer efficiency and orbital offset efficiency, complex factors such as impact energy, timing, and impact point need to be considered. How can it be evaluated? This requires obtaining three-dimensional morphology information of the impact crater and accurately measuring and determining the precise orbit information of the asteroid after the impact. However, when faced with the characteristics of fast spin and similar morphology and texture of small celestial bodies, obtaining this information is not an easy task. Huang Xiangyu, a researcher at the Beijing Institute of Control Engineering, believes that intelligent control technology for close range detection of small celestial bodies will play an important role. With the increasing number of scenarios for close range exploration of small celestial bodies, navigation and control technology is developing towards higher autonomy, intelligence, and multi task adaptability. Technologies such as intelligent collaborative perception, intelligent fusion navigation, and integration of intelligent perception and control decision-making are possible directions for future development. How can I explain it clearly? Wang Chi said that this requires a scientific assessment of the potential risks of fragmentation and disintegration after an impact, as well as the potential long-term orbital evolution risks. In this regard, it is necessary to actively engage in international cooperation on cutting-edge scientific issues in the field of asteroid defense. Wu Weiren also suggested vigorously promoting international exchanges and cooperation in asteroid defense, and jointly building an international integrated monitoring network for space and earth. We need to achieve joint implementation of tasks, joint development of products, joint loading of scientific payloads, and sharing of mission data, "said Wu Weiren." This is a common cause for all mankind. "Although Tianwen-2's breakthrough key technology faces many challenges, the dream of building a high-level Chinese asteroid defense system is becoming a reality. Not long ago, the Tianwen-2 mission probe of China's planetary exploration project arrived at the Xichang Satellite Launch Center and is scheduled to be launched in the first half of this year. According to the plan, Tianwen-2 mission will carry out multiple tasks such as the companion flight, sampling, return, and main belt comet 311P exploration of the near Earth asteroid 2016 HO3 through a single launch. Li Fei from China Aerospace Science and Technology Corporation introduced that Tianwen-2 has broken through the main key technologies of small body detection in areas such as capturing and autonomously rendezvous with weak asteroid targets, autonomous navigation for close range exploration of weak gravity asteroids, reliable attachment and fixation of weak gravity small body surfaces, inversion and 3D reconstruction of in orbit target characteristics, and autonomous management of probes with complex mission modes. It will lay a technical foundation for subsequent asteroid defense missions. The attending experts call for organizing domestic and foreign experts to discuss follow-up tasks as soon as possible, launching major national projects for asteroid defense, and strengthening research on near Earth asteroids. This not only concerns the bottom line of human survival safety and the survival of civilization, but also the answers to major scientific questions such as the origin of the solar system. Ji Jianghui said that the formation of asteroid populations is closely related to the collision history between asteroids in the main belt, which can provide important and reliable constraints on the formation history of planetary systems in the solar system. Identifying asteroid populations and determining their ages using orbital mechanics characteristics and material composition lines is an important direction of current research, while exploring the origin and evolution of near Earth asteroids is a key scientific issue worthy of attention. Guarding the land beneath our feet and gazing up at the starry sky above us, Chinese scientists have been on the road. (New Society)