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arXiv 1308.1990astro-ph.EP
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妊神星卫星的动力学和起源

On the Dynamics and Origin of Haumea's Moons

Matija Ćuk, Darin Ragozzine, David Nesvorný

摘要:

矮行星妊神星有两颗大型卫星,Namaka和Hi'iaka,它们的轨道间距相对较大。这两颗卫星都有显著的偏心率和倾角,其模式与过去的轨道共振一致(Ragozzine和Brown,2009)。根据我们的分析,我们发现,目前的系统是不一致的卫星形成接近的主要和潮汐演化,通过平均运动共振。我们认为纳马卡只经历了有限的潮汐演化,导致相互8:3平均运动共振,重新分配偏心率和倾斜度之间的卫星。这种情况下需要Hi'iaka的原始轨道是轻微的偏心,我们建议,这种偏心率要么是原始的或收购,虽然遇到其他TNO。动力学稳定性和我们首选的潮汐演化模型都意味着卫星的质量只有以前估计值的一半左右,这表明高的重力和低的密度。由于这些卫星目前的轨道强烈暗示它们是从一个靠近它们目前位置的扁平圆盘形成的,我们得出结论,Hi'iaka和Namaka可能是第二代卫星,在过去的一个大卫星解体后形成,以前被认为是妊神星家族的母体(Schlichting和Sari,2009)。我们推导出该卫星的合理参数,与目前的妊神星形成模型一致(Leinhardt et al,2010)。这个假设的一个有趣的含义是,Hi'iaka和Namaka可能相对于妊神星的自转而逆行。妊神星卫星的逆行轨道将与现有的观测和我们的动力学分析完全一致,并且可以为该家族的起源提供一个独特的确认“中断卫星”的场景。

英文摘要:

The dwarf planet Haumea has two large satellites, Namaka and Hi'iaka, which orbit at relatively large separations. Both moons have significant eccentricities and inclinations, in a pattern that is consistent with a past orbital resonance (Ragozzine and Brown, 2009). Based on our analysis, we find that the present system is not consistent with satellite formation close to the primary and tidal evolution though mean-motion resonances. We propose that Namaka experienced only limited tidal evolution, leading to the mutual 8:3 mean-motion resonance which redistributed eccentricities and inclinations between the moons. This scenario requires that the original orbit of Hi'iaka was mildly eccentric; we propose that this eccentricity was either primordial or acquired though encounters with other TNOs. Both dynamical stability and our preferred tidal evolution model imply that the moons' masses are only about one half of previously estimated values, suggesting high albedos and low densities. As the present orbits of the moons strongly suggest formation from a flat disk close to their present locations, we conclude that Hi'iaka and Namaka may be second-generation moons, formed after the breakup of a past large moon, previously proposed as the parent body of the Haumea family (Schlichting and Sari, 2009). We derive plausible parameters of that moon, consistent with the current models of Haumea's formation (Leinhardt et al, 2010). An interesting implication of this hypothesis is that Hi'iaka and Namaka may orbit retrograde with respect to Haumea's spin. Retrograde orbits of Haumea's moons would be in full agreement with available observations and our dynamical analysis, and could provide a unique confirmation the "disrupted satellite" scenario for the origin of the family.

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