冥卫一潮汐阻尼对冥王星三个卫星轨道的影响
The Effect of Charon's Tidal Damping on the Orbits of Pluto's Three Moons
摘要：
冥王星最近发现的小卫星尼克斯和九头蛇几乎都有圆形的轨道，并且几乎与冥王星的主卫星卡戎共面。这是令人惊讶的，因为与冥王星的潮汐相互作用太弱，无法抑制它们的偏心率。我们考虑另一种可能性：尼克斯和九头蛇圆他们的轨道通过激发冥卫一的偏心率通过长期的相互作用，冥卫一反过来又阻尼自己的偏心率与冥王星的潮汐相互作用。这一过程的时间尺度可能小于太阳系的年龄，因为潮汐参数和月球质量是合理的。然而，正如我们通过数值和分析所显示的那样，尼克斯和卡隆之间的2：1和3：1共振强迫项的影响使这幅图复杂化了。在冥卫一潮汐阻尼的存在下，2：1项迫使Nix向外迁移，3：1项改变偏心阻尼率，有时导致偏心增长。我们的结论是，这种机制可能无法解释尼克斯和九头蛇目前的轨道。相反，我们认为它们是在原地形成的，具有低偏心率。我们还表明，尼克斯迁移速度的上限设定了冥王星-冥卫一潮汐循环时间尺度的下限，即>10^5年。此外，水螅观测到的适当偏心率可以用尼克斯的3：2强迫来解释。
英文摘要：
Pluto's recently discovered minor moons, Nix and Hydra, have almost circular orbits, and are nearly coplanar with Charon, Pluto's major moon. This is surprising because tidal interactions with Pluto are too weak to damp their eccentricities. We consider an alternative possibility: that Nix and Hydra circularize their orbits by exciting Charon's eccentricity via secular interactions, and Charon in turn damps its own eccentricity by tidal interaction with Pluto. The timescale for this process can be less than the age of the Solar System, for plausible tidal parameters and moon masses. However, as we show numerically and analytically, the effects of the 2:1 and 3:1 resonant forcing terms between Nix and Charon complicate this picture. In the presence of Charon's tidal damping, the 2:1 term forces Nix to migrate outward and the 3:1 term changes the eccentricity damping rate, sometimes leading to eccentricity growth. We conclude that this mechanism probably does not explain Nix and Hydra's current orbits. Instead, we suggest that they were formed in-situ with low eccentricities. We also show that an upper limit on Nix's migration speed sets a lower limit on Pluto-Charon's tidal circularization timescale of >10^5 yrs. Moreover, Hydra's observed proper eccentricity may be explained by the 3:2 forcing by Nix.
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