According to foreign media reports, it is well known that the asteroid hit the Earth 65 million years ago, resulting in the extinction of dinosaurs, because they have no early warning mechanism and no way to protect themselves. Obviously, humans are trying to avoid the same fate as dinosaurs < p > < / P > < p > to this end, NASA will launch a mission later this year to practice how to derail asteroids that may hit the earth in the future. The mission is called "double asteroid redirection test" (DART), and the unmanned spacecraft is planned as early as November 24 (February 2022 at the latest) It will take one year to reach the target, dimorphos. The asteroid is about the size of a stadium and runs around a larger planet called Didymos. < / P > < p > NASA plans to hit Didymos with a car sized dart spacecraft weighing about 330 kg at a speed of 6.5 kilometers per second, changing its orbit around Didymos for nearly 12 hours by a few minutes. Five years later, Europe NASA's Hera mission spacecraft will arrive at the site to check whether the mission is successful. The impact will only have a small impact on the dimorphos orbit, but it should be enough to make the asteroid deviate from the orbit that hit the earth in the future. Tom Statler, a scientist of NASA dart project, said: "we are doing this to have the ability to prevent a real disaster." < / P > < p > scientists have fully studied the potential changes of dimorphos orbit. But so far, we don't know what changes will happen to dimorphos itself after impact. By Harrison agrusa, a professor at the University of Maryland The leading researchers simulated the change of dimorphos itself by calculating how the momentum of the impact changed the roll, pitch and yaw of the asteroid. The result may be dramatic. Aglusa said: "it may start to rotate and enter a state of chaos." < / P > < p > this unexpected rotation poses many interesting challenges. For example, it will increase the difficulty of landing on the asteroid. The European space agency hopes to use two small spacecraft to try to land the asteroid during its Hera mission. It may also complicate future attempts to derail asteroids that hit the earth, because any rotation may affect the asteroid's orbit Path in space. < / P > < p > when the dart spacecraft hit dimorphos, its impact energy was equivalent to the explosion of three tons of TNT explosives, spraying thousands of pieces of debris into space. Professor stattler described that it was like a golf cart hitting a football field at a speed of 24000 kilometers per hour. Aglusa and his team said that the impact force would not immediately change the rotation of dimorphos, but Within a few days, the situation will begin to change dramatically. < / P > < p > soon, dimorphos will begin to shake slightly. This swing will be larger and larger, because the momentum from the impact makes the rotation of dimorphos out of balance, and there is no friction in the vacuum to slow it down. Dimorphos may start to rotate in a single direction or along the long axis similar to a barbecue rack. For observation For the, the seemingly calm satellite will take on a new form, start to swing back and forth violently, and its previously hidden side will appear. < / P > < p > in a few weeks, the rotation of dimorphos will become more intense, so that it will fall into a chaotic tumbling state and rotate uncontrollably around its axis. In more extreme cases, the tidal effect of Didymos may be eliminated If it is completely broken, dimorphos may begin to turn over completely. < / P > < p > what will happen depends on many factors. The shape of dimorphos will play an important role: if it is more slender than spherical, it will rotate more disorderly. So far, radar observations show that dimorphos is slender, but we won't know until a few hours before dart spacecraft hits it. < / P > < p > collision The location of the strike is also critical. The dart spacecraft will aim at the center of dimorphos with the goal of applying maximum force to change its orbit. However, the more the impact point deviates from the center, the more chaotic the spin generated by dimorphos will be. However, in most cases, dimorphos should swing back and forth playfully or roll in multiple directions within a few weeks. < / P > < p > five years later, when the European Space Agency's space agency When the spacecraft arrives, the scene may be quite dramatic. Due to human influence, Didymos may rotate wildly in its orbit. It may take decades or even centuries for Didymos's gravity to restore dimorphos to its original state, that is, the state locked by the tide. < / P > < p > the arrival of Hera spacecraft will enable us to determine what changes have taken place in dimorphos itself The only way to realize the impact is because the dart spacecraft will be destroyed by the impact, and dimorphos is too small to be observed in detail from the earth. The Italian made liciacube small satellite will be deployed before the impact and will take images when the impact roars out, but it can only take images for a few minutes, which is not enough to observe the subsequent impact of the impact. < / P > < p > The Hera mission also plans to deploy two satellites Smaller satellites, trying to land on the surface of dimorphos. The tumbling motion is not expected to hinder these efforts, but may make them more difficult. Without proper planning for this chaotic rotation, the satellite may bounce around and eventually fail to reach the position desired by scientists. Patrick Michel of the French National Center for scientific research (CNRS) "In any case, landing on such a small object is very difficult," Patrick Michel said < / P > < p > the rotational motion of dimorphos is not expected to affect the dress rehearsal of dart spacecraft to save the earth, nor pose any danger to the earth, but it will provide a lot of scientifically useful information. The spin state of asteroids may affect other properties, such as how much sunlight they reflect, which may affect their orbit, which may also be the orbit deflection of asteroids in the future "It's not as simple as letting a spacecraft hit an asteroid. You need to understand a lot of physics," said Paul wiegert, an astronomer at the University of Western Ontario < / P > < p > observing this system for many years, decades or even centuries will also give us an unprecedented opportunity to see how the double asteroid system will change after such an impact. The Hera mission spacecraft can observe how strong the tidal effect is in the process of restoring the system to normal, and help us understand two small asteroids like this The gravitational relationship between planets. (small) < / P > < p >