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arXiv 1402.0625astro-ph.EP
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冥王星-冥卫一的完整潮汐演化

Complete Tidal Evolution of Pluto-Charon

W. H. Cheng, Man Hoi Lee, S. J. Peale

摘要:

冥王星和它的卫星冥卫一的自转速率与它们的轨道平均运动同步。这是潮汐演化的理论终点,角动量的转移已经停止。在这里,我们遵循冥王星的潮汐演化从一个初始状态具有当前的系统的总角动量,但与冥卫一在偏心轨道与半长轴$a \approx 4R_P$(其中$R_P$是冥王星的半径),符合其影响的起源。使用两种潮汐模型,其中潮汐耗散函数$Q \propto$ 1/频率和$Q=$常数,其中演化的细节强烈依赖于模型。在分析中包含的引力调和系数$C_{22}$的两个机构允许顺利,自洽的演化的双重同步状态,而它的省略挫败成功的演化在某些情况下。也可以包括带状谐波$J_2$,但不会对整体演化产生显著影响。冥卫一与冥王星的耗散比控制着轨道偏心率的行为,在最后接近双同步旋转之前,一个明智的选择会导致一个几乎恒定的偏心率。潮汐模型是完整的,在这个意义上,潮汐演化的每一个细微差别都是在守恒总角动量的情况下实现的--包括当冥卫一的自旋减小时,暂时捕获到自旋轨道共振中,并阻尼了相同的振动。

英文摘要:

Both Pluto and its satellite Charon have rotation rates synchronous with their orbital mean motion. This is the theoretical end point of tidal evolution where transfer of angular momentum has ceased. Here we follow Pluto's tidal evolution from an initial state having the current total angular momentum of the system but with Charon in an eccentric orbit with semimajor axis $a \approx 4R_P$ (where $R_P$ is the radius of Pluto), consistent with its impact origin. Two tidal models are used, where the tidal dissipation function $Q \propto$ 1/frequency and $Q=$ constant, where details of the evolution are strongly model dependent. The inclusion of the gravitational harmonic coefficient $C_{22}$ of both bodies in the analysis allows smooth, self consistent evolution to the dual synchronous state, whereas its omission frustrates successful evolution in some cases. The zonal harmonic $J_2$ can also be included, but does not cause a significant effect on the overall evolution. The ratio of dissipation in Charon to that in Pluto controls the behavior of the orbital eccentricity, where a judicious choice leads to a nearly constant eccentricity until the final approach to dual synchronous rotation. The tidal models are complete in the sense that every nuance of tidal evolution is realized while conserving total angular momentum - including temporary capture into spin-orbit resonances as Charon's spin decreases and damped librations about the same.

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