Libration and migration of propeller moons in Saturns dense rings

卡西尼号任务最有趣的发现之一是最大螺旋桨小卫星的非开普勒过量运动。在第一个项目阶段的研究表明，这些纵向天平动可能是由许多土星卫星引起的近共振扰动激发的，而环-小卫星相互作用有可能放大天平动振幅，正如我们的线性化小卫星-螺旋桨模型所建议的那样。在继续阶段，我们计划完成我们的数值模拟的共振驱动的小卫星天平动，通过将耗散效应模仿众多的不可逆的小卫星环的相互作用（物理碰撞，引力散射）。通过这种方法，可以预期静态振动特性，并且它们对耗散率的依赖可以帮助识别主导振动。这些特定的天平动振幅的放大-在前一个项目阶段中由线性化的小卫星螺旋桨振荡器的单一模式所证明-现在将通过小卫星在密集颗粒环流体中自由移动的流体动力学模拟来建模。这种方法将使我们能够捕获的小卫星螺旋桨相互作用，这可能会允许多个（相互作用）天平动模式的兴奋和放大的非线性字符。此外，我们将比较相关的结果与目前的卡西尼成像数据。

One of the most interesting findings of the Cassini-mission has been a Non-Keplerian excess motion of the largest propeller moonlets. Studies in the first project phase have indicated that these longitudinal librations might be excited by near-resonant perturbations caused by the numerous Saturnian satellites, while ring-moonlet interactions have the potential to amplify the libration amplitude, as suggested by our linearized moonlet-propeller model. In the continuation phase we plan to complete our numerical modeling of the resonantly driven moonlet-libration by incorporating dissipative effects mimicking the numerous irreversible moonlet-ring interactions (physical collisions, gravitational scattering). With this approach stationary libration properties can be expected and their dependence on the dissipation rate could help to identify dominating librations. The amplification of these certain libration amplitudes - demonstrated by the linearized moonlet-propeller oscillator for a single mode in the previous project phase - will now be modeled by hydrodynamic simulations of a moonlet freely moving in a dense granular ring-fluid. This approach will permit us to capture the non-linear character of the moonlet-propeller interactions, which may allow the excitement and amplification of multiple (interacting) libration modes. Further, we will compare the related results with the current Cassini imaging data.