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arXiv 1503.06805astro-ph.EP
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冥王星-冥卫一双星环的演化

Evolution of a ring around the Pluto-Charon binary

B. C. Bromley, S. J. Kenyon

摘要:

我们考虑形成的卫星周围的冥王星-冥卫一二。这两个伙伴之间的早期碰撞可能产生了双星和一个狭窄的碎片环,其中出现了卫星冥河,尼克斯,伊兹密尔和九头蛇。卫星是如何从致密环中出现的还不确定。在这里,我们表明,一个粒子环传播的物理碰撞和集体引力散射,类似于迁移。在双星系统周围,这些过程发生在“最圆”轨道的参考系中,类似于开普勒势中的圆形轨道。星环的粒子在这些轨道上运动,避免了毁灭性的碰撞。阻尼和扩散也有助于粒子在与双星共振驱动的动力学不稳定性中幸存下来。在某些情况下,粒子被困在共振附近,随着冥王星-冥卫一双星的潮汐演化而向外扫过。通过简单的模型和数值实验,我们展示了冥王星-冥卫一撞击环是如何扩展成一个宽阔的圆盘的,而环双星就是从这个圆盘中生长出来的。在某些情况下,环可以远远超出最远的卫星Hydra的轨道,形成少数较小的卫星。如果这些小卫星存在,新视野号将找到它们。

英文摘要:

We consider the formation of satellites around the Pluto-Charon binary. An early collision between the two partners likely produced the binary and a narrow ring of debris, out of which arose the moons Styx, Nix, Kerberos and Hydra. How the satellites emerged from the compact ring is uncertain. Here we show that a particle ring spreads from physical collisions and collective gravitational scattering, similar to migration. Around a binary, these processes take place in the reference frames of "most circular" orbits, akin to circular ones in a Keplerian potential. Ring particles damp to these orbits and avoid destructive collisions. Damping and diffusion also help particles survive dynamical instabilities driven by resonances with the binary. In some situations, particles become trapped near resonances that sweep outward with the tidal evolution of the Pluto-Charon binary. With simple models and numerical experiments, we show how the Pluto-Charon impact ring may have expanded into a broad disk, out of which grew the circumbinary moons. In some scenarios, the ring can spread well beyond the orbit of Hydra, the most distant moon, to form a handful of smaller satellites. If these small moons exist, New Horizons will find them.

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