All asteroid spins evolve due to collisions. Geophysical analysis (Mao and McKinnon 2018b) implies Ceres might have been modestly despun (by ~6.5%) by impacts. Vesta’s postaccretion rotation rate, before the formation of the Veneneia and Rheasilvia basins, has also been proposed to have been higher (by ~6%) than today (Fu et al. 2014). We have designed Monte Carlo simulations to investigate Ceres’ and Vesta’s plausible spin evolution by impacts. We use the main belt asteroid size–frequency distribution, Ceres’ and Vesta’s cratering records, and their present‐day impact velocity probability distributions to quantify possible spin histories. We consider dynamical effects from escaping ejecta, adopt mass‐velocity scaling laws for two endmember surface materials (porous and nonporous), and track potential catastrophic disruptions. Results show that Ceres’ spin period likely changed by a fraction of an hour (up or down) compared with its “initial,” accretional spin, mostly due to large impacts. Different surface materials do not yield statistically distinguishable final spin distributions, but imply opposite crustal evolutions where Ceres loses/accretes mass, depending on surface porosity; as much as several 100 m worth of exogenous material, globally averaged, can be accreted if the surface remains porous. Vesta’s final Monte Carlo spin distribution is more concentrated around its “initial” value, possibly implying a more relict spin state than Ceres. However, explicitly modeling the angular momentum changes wrought by Vesta’s two existing planetary‐scale impact basins shows that their formation alone can account for Vesta’s proposed spindown, although spinup is a much more likely outcome because of the scale and location of the impacts.

中文翻译：

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谷神星和维斯塔的自旋进化

所有小行星自旋由于碰撞而演化。地球物理分析（Mao和McKinnon 2018b）表明，谷神星可能受到撞击的影响很小（〜6.5％）。在Veneneia和Rheasilvia盆地形成之前，Vesta的增生后旋转速率也被提出比今天更高（〜6％）（Fu等人，2014）。我们设计了蒙特卡洛模拟，以通过撞击研究谷神星和维斯塔的合理自旋演化。我们使用主带小行星的大小－频率分布，Ceres和Vesta的陨石坑记录以及它们当前的撞击速度概率分布来量化可能的自旋历史。我们考虑了逃逸喷射产生的动力影响，对两个端构件表面材料（多孔和无孔）采用了质量比例定律，并跟踪了潜在的灾难性破坏。结果表明，谷神星的自转周期与其“初始”增生自旋相比可能变化了一个小时（上下），这主要是由于影响较大。不同的表面物质不能产生统计上可区分的最终自旋分布，但是暗示着地壳演化的相反，根据表面孔隙度，谷神星失去/增加了质量。如果表面仍然是多孔的，则可以吸收多达全球平均数达100 m的外源物质。维斯塔（Vesta）的最终蒙特卡洛自旋分布更集中在其“初始”值附近，这可能意味着比塞雷斯（Ceres）更残lic的自旋态。但是，对维斯塔两个现有行星尺度撞击盆地造成的角动量变化进行显式建模表明，仅它们的形成就可以解释维斯塔提议的旋降，