Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA.
Department of Astronomy, University of Maryland, College Park, MD, USA.
Nature. 2023 Apr;616(7957):457-460. doi: 10.1038/s41586-023-05878-z. Epub 2023 Mar 1.
The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on 26 September 2022 as a planetary defence test. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. Here we report a determination of the momentum transferred to an asteroid by kinetic impact. On the basis of the change in the binary orbit period, we find an instantaneous reduction in Dimorphos's along-track orbital velocity component of 2.70 ± 0.10 mm s, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact. For a Dimorphos bulk density range of 1,500 to 3,300 kg m, we find that the expected value of the momentum enhancement factor, β, ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m, [Formula: see text]. These β values indicate that substantially more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.
美国宇航局双小行星重定向测试（DART）任务于 2022 年 9 月 26 日世界协调时 23 时 14 分对双小行星（65803）Didymos 的卫星 Dimorphos 进行了动能撞击，这是一次行星防御测试。DART 是首次在与行星防御相关的小行星大小和速度范围内进行的超高速撞击实验，旨在验证动能撞击作为一种小行星偏转手段的有效性。在这里，我们报告了通过动能撞击传递给小行星的动量的确定。根据双星轨道周期的变化，我们发现 Dimorphos 的沿迹轨道速度分量瞬时减少了 2.70±0.10mm/s，表明由于撞击产生的喷射流的反冲，动量传递增强。对于 Dimorphos 的体密度范围在 1500 到 3300kg/m3 之间，我们发现，由于动量增强因子β的值在 2.2 到 4.9 之间，取决于 Dimorphos 的质量。如果假设 Dimorphos 和 Didymos 的密度相等，均为 2400kg/m3，[公式：见正文]。这些β值表明，从逃逸的撞击喷射物传递到 Dimorphos 的动量比与 DART 相撞的动量多得多。因此，DART 的动能撞击在偏转小行星 Dimorphos 方面非常有效。
