Recent spacecraft and radar observations found that ∼70% of short-period comet nuclei, mostly Jupiter-family comets (JFCs), have bilobate shapes (two masses connected by a narrow neck). This is in stark contrast to the shapes of asteroids of similar sizes, of which ∼14% are bilobate. This suggests that a process or mechanism unique to comets is producing these shapes. Here we show that the bilobate shapes of JFC nuclei are a natural byproduct of sublimative activity during their dynamical migration from their trans-Neptunian reservoir, through the Centaur population, and into the Jupiter family. We model the torques resulting from volatile sublimation during this dynamical migration, and find that they tend to spin up these nuclei to disruption. Once disrupted, the rubble pile-like material properties of comet nuclei (tensile strengths of ∼1–10 Pa and internal friction angles of ∼35) cause them to reform as bilobate objects. We find that JFCs likely experienced rotational disruption events prior to entering the Jupiter family, which could explain the prevalence of bilobate shapes. These results suggest that the bilobate shapes of observed comets developed recently in their history (within the past ∼1–10 Myr), rather than during solar system formation or collisions during planet migration and residency in the trans-Neptunian population.

最近的航天器和雷达观测发现，约 70% 的短周期彗星核，主要是木星家族彗星 (JFC)，具有双叶形（两个质量由窄颈连接）。这与大小相似的小行星的形状形成鲜明对比，其中约 14% 是双叶行星。这表明彗星特有的过程或机制正在产生这些形状。在这里，我们展示了 JFC 核的双叶形状是它们从跨海王星水库、半人马座种群并进入木星家族的动态迁移过程中升华活动的天然副产品。我们对这种动态迁移过程中挥发性升华产生的扭矩进行建模，并发现它们往往会使这些原子核旋转到破裂。一旦被打扰，彗核的碎石堆状材料特性（抗拉强度为~1-10 Pa，内摩擦角为~35）使它们重新形成双叶物体。我们发现 JFC 可能在进入木星家族之前经历了旋转中断事件，这可以解释双叶形状的流行。这些结果表明，观察到的彗星的双叶形状是在其历史上最近发展起来的（在过去的~1-10 Myr 内），而不是在太阳系形成或行星迁移和居住在跨海王星群体中的碰撞期间。