土星共轨卫星Janus和Epimetheus物理天平动的解析描述
Analytical description of physical librations of Saturnian coorbital satellites Janus and Epimetheus
摘要：
雅努斯和厄庇墨透斯以其独特的马蹄形轨道而闻名，这是由1：1的轨道共振造成的。每隔四年，这两颗卫星就会因为近距离相遇而交换几十公里的轨道。最近，Tiscareno等人（2009年）提出了一个基于卡西尼轨道器图像的旋转模型。这些作者通过将一个形状模型与最近的卡西尼国际空间站图像相拟合，推断出轨道周期内经度上旋转平动的幅度。通过准周期近似的轨道运动，我们描述了轨道交换如何影响卫星的旋转。为了这个目的，我们已经开发了一个形式主义的基础上的准周期序列的长周期和短周期的振动。在这个框架中，在轨道周期的天平动的振幅被发现成比例的轨道交换占一项。我们检查了分析准周期发展进行数值模拟，发现两个结果吻合良好。为了完成这项研究，关于短周期振动的结果进行了研究的帮助下绝热的方法。
英文摘要：
Janus and Epimetheus are famously known for their distinctive horseshoe-shaped orbits resulting from a 1:1 orbital resonance. Every four years these two satellites swap their orbits by a few tens of kilometers as a result of their close encounter. Recently Tiscareno et al. (2009) have proposed a model of rotation based on images from the Cassini orbiter. These authors inferred the amplitude of rotational librational motion in longitude at the orbital period by fitting a shape model to the recent Cassini ISS images. By a quasiperiodic approximation of the orbital motion, we describe how the orbital swap impacts the rotation of the satellites. To that purpose, we have developed a formalism based on quasi-periodic series with long and short-period librations. In this framework, the amplitude of the libration at the orbital period is found proportional to a term accounting for the orbital swap. We checked the analytical quasi-periodic development by performing a numerical simulation and find both results in good agreement. To complete this study, the results regarding the short-period librations are studied with the help of an adiabatic-like approach.
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