美国亚利桑那大学Denton C. Adeene的团队近日数值模拟了绕冥王星的古卡戎被捕获的过程。相关论文于2025年1月6日发表在《自然—地球科学》杂志上。

据了解，冥王星和卡戎是已知外太阳系外海王星天体中最大的双星系统。它们共享的外轨道轴表明，它们的进化史和碰撞起源是有联系的。它们的半径分别约为1200km和约为600km，而卡戎的宽圆轨道大约是冥王星半径的16倍，这就需要一种形成机制，将大质量分数置于轨道上，并具有足够的角动量来驱动潮汐轨道膨胀。

在这里，研究团队通过包括物质强度在内的模拟，对冥王星撞击卡戎被捕获的过程进行了数值模拟。在模拟中，摩擦分配了撞击的动量，导致卡戎和冥王星暂时连接在一起，而不是合并，因为撞击与目标的旋转一致。在这种“亲吻和俘获”的制度下，身体的结合被力量所阻止。

对于与系统角动量一致的前进目标旋转，卡戎然后潮汐解耦并上升到一个近圆轨道，从它向外迁移到与当前轨道一致的距离。在这种情况下，卡戎相对完整地被捕获，保留了它的核心和大部分地幔，这意味着卡戎可能和冥王星一样古老。

附：英文原文

Title: Capture of an ancient Charon around Pluto

Author: Denton, C. Adeene, Asphaug, Erik, Emsenhuber, Alexandre, Melikyan, Robert

Issue&Volume: 2025-01-06

Abstract: Pluto and Charon are the largest binary system in the known population of trans-Neptunian objects in the outer Solar System. Their shared external orbital axis suggests a linked evolutionary history and collisional origin. Their radii, ~1,200km and ~600km, respectively, and Charon’s wide circular orbit of about 16 Pluto radii require a formation mechanism that places a large mass fraction into orbit, with sufficient angular momentum to drive tidal orbital expansion. Here we numerically model the collisional capture of Charon by Pluto using simulations that include material strength. In our simulations, friction distributes impact momentum, leading Charon and Pluto to become temporarily connected, instead of merging, for impacts aligned with the target’s rotation. In this ‘kiss-and-capture’ regime, coalescence of the bodies is prevented by strength. For a prograde target rotation consistent with the system angular momentum, Charon is then tidally decoupled and raised into a near-circular orbit from which it migrates outwards to distances consistent with its present orbit. Charon is captured relatively intact in this scenario, retaining its core and most of its mantle, which implies that Charon could be as ancient as Pluto.

DOI: 10.1038/s41561-024-01612-0

Source: https://www.nature.com/articles/s41561-024-01612-0