小行星防御动能撞击效果评估

以动能撞击防御潜在威胁小行星概念为背景,采用物质点法(Material Point Method,MPM)模拟了铝弹高速撞击S型小行星的过程,将撞击结果导入引力N体–离散元动力学模型中,对其后续演化过程进行仿真,并分析了撞击后碎片对地球的威胁指数。结果显示小行星在高速撞击的作用下部分破碎,大量碎片以与撞击方向相反的速度向外喷射,从而提升了小行星的撞击偏移效果。研究采用了两种不同结构的小行星模型:完整结构(monolithic structure)的小行星在遭受撞击后会喷射出比原小行星小得多的碎片,而碎石堆结构(rubble-pile structure)的小行星在撞击作用下可分裂成大小和速度分布较为均匀的碎片。威胁指数的分析表明动能撞击方式确实有效减小了小行星的威胁程度,撞击后的最大剩余碎片可被成功偏移至安全轨道,但仍有部分碎片会与地球相撞。与完整结构相比,针对碎石堆结构小行星的撞击防御的总体效果更好,次生灾害主要为大质量碎片的撞击。研究方法可用于未来开展防御小行星的动能撞击任务的撞击条件选择和撞击结果预估。

Evaluation of Effects of Kinetic Impact Deflection on Hazardous Asteroids

The kinetic impact deflection would result in a number of unexpected hazardous fragments. For this reason, understanding the outcomes of impact is fundamental to assess the effects of this mitigation technique. The process of hyper-velocity impact of a small artificial aluminum projectile on an S-type asteroid is investigated with the material point method(MPM). In order to evaluate the impact threat of the resulting fragments posed to the Earth, the impact outcomes are transferred to the heliocentric orbit of a hazardous asteroid. A parallel N-body code is applied to propagate the evolution of these fragments in the solar system. The impact hazard of the fragments on the Earth is analyzed and the role of asteroid interior structures is explored. The results show that the structure of the simulated body is partially destroyed by the kinetic impactor. Some of the resulting fragments move backward along the impact direction, enhancing the deflection efficiency. Furthermore, the collision outcomes proved to be very dependent on the internal structure of the asteroid. The fragments produced from the monolithic target are much smaller than those from the rubble-pile one, while the size and speed distribution of fragments in the former case is steeper and smaller. The hazard assessment implies that although the impact damage to the Earth is reduced from the deflection, there are still a number of small resulting fragments posing threat to the Earth. The expected damage caused by the deflected monolithic target is larger than the rubble-pile target because of the exist of numerous small dangerous fragments. The method presented in this study can be used to infer the impact condition and outcomes in future planetary defense missions.