The New Horizons spacecraft’s flyby of Kuiper belt object (486958) Arrokoth revealed a bilobed shape with highly flattened lobes both aligned to its equatorial plane, and a rotational axis almost aligned to the orbital plane (obliquity ~99°)^1,2,3,4. Arrokoth belongs to the cold classical Kuiper belt object population that occupies dynamically undisturbed orbits around the Sun, and as such is a primitive object that formed in situ. Therefore, whether its shape is primordial or evolutionary carries important implications for understanding the evolution of both Kuiper belt objects and potentially their dynamically derived objects, Centaurs and Jupiter-family comets^5,6. Applying our mass-loss-driven shape evolution model (MONET)⁷, here we suggest that the current shape of Arrokoth could be of evolutionary origin due to volatile outgassing in a timescale of about 1–100 Myr, while its spin state would not be dramatically affected. We further argue that such a process may be ubiquitous in the evolution of the shape of Kuiper belt objects shortly after their formation. This shape-changing process could also be reactivated when Kuiper belt objects dynamically evolve to become Centaurs and then Jupiter-family comets^5,6 and receive markedly increased solar heating.

新视野号飞船飞越了柯伊伯带天体（486958）阿罗科斯（Arrokoth），发现了双叶形状，高度平坦的裂片均对准其赤道平面，旋转轴几乎对准了轨道平面（倾角约99°）^{1,2,3， 4}。Arrokoth属于寒冷的古典柯伊伯带天体，它占据了绕太阳动态无扰动的轨道，因此是原位形成的原始天体。因此，无论其形状是原始的还是演化的，对于理解柯伊伯带天体的演化以及潜在地它们的动态衍生天体，半人马座和木星家庭彗星^5,6的演化都具有重要意义。应用我们的质量损失驱动的形状演化模型（MONET）⁷，在这里我们建议Arrokoth的当前形状可能是由于在大约1–100 Myr的时间范围内挥发出气而形成的演化起源，而其自旋态不会受到显着影响。我们进一步认为，这一过程可能在柯伊伯带天体形成后不久的形状演化中无处不在。当柯伊伯带天体动态演变成半人马座，然后成为木星家族彗星^5,6并获得明显增加的太阳热量时，也可以重新激活这种形状变化过程。