Formation of Moons and Equatorial Ridge around Top-shaped Asteroids after Surface Landslide
Formation of Moons and Equatorial Ridge around Top-shaped Asteroids after Surface Landslide
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DOI：
10.3847/2041-8213/ac922d
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发表时间：
2022-10-01
影响因子：
7.9
通讯作者：
Sugiura, Keisuke
中科院分区：
文献类型：
--
作者：
Hyodo, Ryuki;Sugiura, Keisuke
在近地小行星中观察到了顶部形状的小行星。据报道，它们中约有一半具有卫星（约为1重量%）。其中许多都有一个赤道脊。最近的一项研究表明，神秘的顶部形状的小行星（例如，Ryugu，Bennu和Didymos）可能是由于在分裂旋转期间附近的快速自旋期间的主要轴对称滑坡。这样的滑坡将不可避免地在小行星周围形成一个短时间尺度（类似于3小时）的微粒盘。然而，长期的完整的动力学演化没有调查。在这里，我们进行了连续模拟（类似于700小时），调查从表面滑坡，形成一个顶部形状的小行星和颗粒盘到盘的演变事件的顺序。我们表明，磁盘迅速蔓延，并产生月亮（类似于300小时内）。形成的月球的质量与在顶部形状的小行星周围观察到的一致。我们还表明，赤道脊是自然形成的，因为一小部分的磁盘颗粒重新选择性地吸积到赤道地区的主要。我们设想，Ryugu和Bennu可能曾经有一个古老的卫星，后来由于连续的卫星轨道演化而丢失。或者，在一个有卫星的顶部形状的小行星上，如Didymos，没有发生会导致其丢失的重大轨道演变。我们的研究也将定性适用于任何碎石堆小行星附近的分裂旋转周期。
Top-shaped asteroids have been observed among near-Earth asteroids. About half of them are reported to have moons (on the order of similar to 1 wt.% of the top-shaped primary) and many of them have an equatorial ridge. A recent study has shown that the enigmatic top-shaped figure of asteroids (e.g., Ryugu, Bennu, and Didymos) could result from an axisymmetric landslide of the primary during a fast spin-up near the breakup rotation period. Such a landslide would inevitably form a particulate disk around an asteroid with a short timescale (similar to 3 hr). However, the long-term full dynamical evolution is not investigated. Here, we perform a continuous simulation (similar to 700 hr) that investigates the sequence of events from the surface landslide that forms a top-shaped asteroid and a particulate disk to disk evolution. We show that the disk quickly spreads and produces moons (within similar to 300 hr). The mass of the formed moon is consistent with what is observed around the top-shaped asteroids. We also demonstrate that an equatorial ridge is naturally formed because a fraction of the disk particles re-accretes selectively onto the equatorial region of the primary. We envision that Ryugu and Bennu could once have an ancient moon that was later lost due to a successive moon's orbital evolution. Alternatively, at a top-shaped asteroid that has a moon, such as Didymos, no significant orbital evolution of the moon has occurred that would result in its loss. Our study would also be qualitatively applicable to any rubble-pile asteroids near the breakup rotation period.