Enceladus' Icy Plume - The E-Ring Cradle

2005年，卡西尼号宇宙飞船在三次飞掠土卫二的过程中，发现了一个巨大的气体尘埃羽状物，从地质上年轻、伤痕累累、非常温暖的南极地区散发出来。这一独特的探测清楚地表明，土星的E环是在小冰行星土卫二的地球物理活跃的南极。在这个项目中，我们计划建立一个E环粒子起源的模型，目标是推导冰粒的速度和大小分布。其基本思想包括土卫二南极冰壳的地下通道或裂缝中水蒸气中的冰粒的成核、生长和加速。这些研究将包括过饱和气体通道流动的热力学和流体动力学/动力学，固体冰粒从那里稳定地出现。为了重现观测到的尘埃羽流的特性，该模型必须包括允许羽流颗粒与通道壁碰撞等减速的过程。由此产生的粒子的速度和大小分布将决定土卫二羽流的性质，并最终决定随后的动力学和土星E环的外观。通过模拟和分析卡西尼号尘埃羽流和E环数据的迭代方法，我们试图获得地下通道地质和流动动力学的新见解，否则这些新见解将被南极冰所隐藏。此外，我们预计我们的模型预测将对即将到来的卡西尼号航天器在2008年及以后近距离飞越土卫二的计划至关重要。

During three flybys of Enceladus in 2005 the Cassini-spacecraft spotted a gigantic gas-dust plume emanating from a geologically young, scarred and remarkably warm region at the south pole. This unique detection made clear that the Saturn's E ring is seeded in the geo-physically active south pole of the small icy world Enceladus.In this project we plan to develop a model of the origin of the E ring particles with the goal to derive the velocity and the size distribution of the icy grains. The basic ideas include nucleation, growth and acceleration of icy motes in the water vapor in underground channels or cracks perforating the south-polar ice-shell of Enceladus. The studies will incorporate the thermo - and hydrodynamics/kinetics of the channel-flow of the supersaturated gas from where solid ice particles steadily emerge. In order to reproduce the properties of the observed dust plume, the model must include processes which allow for a deceleration of the plume-grains like collisions with the channel walls. The resulting distributions of velocities and sizes of the launched particles will determine the properties of Enceladus' plume and eventually the subsequent dynamics and appearance of the E ring of Saturn.With an iterative approach between modeling and analysis of the Cassini-date of the dust plume and the E ring we try to gain new insights in the underground channel-geology and flow dynamics which otherwise remained hidden by the south-polar ice. Furthermore, we expect that predictions of our modeling will be of vital interest for the planning of the upcoming close flybys of the Cassini spacecraft of Enceladus in 2008 and later.