We explore binary asteroid formation by spin-up and rotational disruption considering the NASA DART mission's encounter with the Didymos–Dimorphos binary, which was the first small binary visited by a spacecraft. Using a suite of N-body simulations, we follow the gravitational accumulation of a satellite from meter-sized particles following a mass-shedding event from a rapidly rotating primary. The satellite’s formation is chaotic, as it undergoes a series of collisions, mergers, and close gravitational encounters with other moonlets, leading to a wide range of outcomes in terms of the satellite's mass, shape, orbit, and rotation state. We find that a Dimorphos-like satellite can form rapidly, in a matter of days, following a realistic mass-shedding event in which only ∼2%–3% of the primary's mass is shed. Satellites can form in synchronous rotation due to their formation near the Roche limit. There is a strong preference for forming prolate (elongated) satellites, although some simulations result in oblate spheroids like Dimorphos. The distribution of simulated secondary shapes is broadly consistent with other binary systems measured through radar or lightcurves. Unless Dimorphos's shape is an outlier, and considering the observational bias against lightcurve-based determination of secondary elongations for oblate bodies, we suggest there could be a significant population of oblate secondaries. If these satellites initially form with elongated shapes, a yet-unidentified pathway is needed to explain how they become oblate. Finally, we show that this chaotic formation pathway occasionally forms asteroid pairs and stable triples, including coorbital satellites and satellites in mean-motion resonances.

中文翻译：

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小小行星周围卫星形成的直接 N 体模拟：DART 与 Didymos 系统相遇的见解

考虑到 NASA DART 任务与 Didymos-Dimorphos 双星的相遇，我们通过旋转和旋转破坏来探索双星小行星的形成，这是航天器访问的第一个小型双星。使用一套氮-体模拟，我们跟踪卫星在快速旋转的主星发生质量脱落事件后米级粒子的引力积累。这颗卫星的形成是混乱的，因为它经历了一系列的碰撞、合并以及与其他小卫星的紧密引力接触，导致卫星的质量、形状、轨道和旋转状态产生各种各样的结果。我们发现，在一次实际的质量脱落事件（其中仅脱落了主星质量的约 2%–3%）之后，类 Dimorphos 卫星可以在几天内迅速形成。由于卫星的形成接近罗希极限，因此卫星可以同步旋转形成。尽管一些模拟结果会产生像 Dimorphos 这样的扁球体，但人们仍然强烈倾向于形成扁长（细长）卫星。模拟二次形状的分布与通过雷达或光曲线测量的其他二元系统大致一致。除非 Dimorphos 的形状是异常值，并且考虑到基于光曲线确定扁球体次生伸长率的观测偏差，我们认为可能存在大量扁球体。如果这些卫星最初形成为细长形状，则需要一条尚未确定的路径来解释它们如何变成扁圆形。最后，我们表明这种混沌形成路径偶尔会形成小行星对和稳定的三颗小行星，包括共轨卫星和平均运动共振卫星。