On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid (65803) Didymos. Numerical simulations of the impact provide a means to find the surface material properties and structures of the target that are consistent with the observed momentum deflection efficiency, ejecta cone geometry and ejected mass. Our simulation that best matches the observations indicates that Dimorphos is weak, with a cohesive strength of less than a few pascals, like asteroids (162173) Ryugu and (101955) Bennu. We find that the bulk density of Dimorphos ρ_B is lower than ~2,400 kg m⁻³ and that it has a low volume fraction of boulders (≲40 vol%) on the surface and in the shallow subsurface, which are consistent with data measured by the DART experiment. These findings suggest that Dimorphos is a rubble pile that might have formed through rotational mass shedding and reaccumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater.

2022 年 9 月 26 日，美国宇航局的双小行星重定向测试 (DART) 任务成功撞击了双态近地小行星 (65803) Didymos 的天然卫星 Dimorphos。撞击的数值模拟提供了一种找到目标表面材料特性和结构的方法，这些特性和结构与观察到的动量偏转效率、喷射锥几何形状和喷射质量一致。我们的模拟与观测结果最相符，表明 Dimorphos 很弱，内聚强度不到几个帕斯卡，就像小行星 (162173) Ryugu 和 (101955) Bennu 一样。我们发现 Dimorphos ρ _B的堆积密度低于约 2,400 kg m ^{− 3} ，并且其表面和浅层地下的巨石体积分数较低 ( ≲ 40 vol%)，这与测量的数据一致通过 DART 实验。这些发现表明，Dimorphos 是一个碎石堆，可能是通过 Didymos 的旋转质量脱落和重新堆积而形成的。我们的模拟表明，DART 撞击导致了 Dimorphos 的整体变形和表面重塑。欧空局即将进行的赫拉任务可能会发现一颗重塑的小行星，而不是一个明确的陨石坑。