The Influence of Mantle Rheology on the Early Differentiation of Icy Satellites

除了围绕外行星运行的22颗主要卫星外，海王星和天王星的主体是以H2O为主但也含有氨和甲烷的冰状物质。这些卫星据信主要是在太阳星云消散之前积累起来的，它们对行星科学特别感兴趣，因为它们显示了一系列不同的地质特征，包括液态海洋、活动板块构造和火山活动的唯一地外证据。这些卫星的不同表面表现反映了自吸积以来活跃的不同内部过程，例如，这导致了内部不同程度的分化。控制早期分化的一个关键参数是通过对流从内部损失的热量。只有那些迅速建立对流系统的天体才能保持足够低的温度，以防止融化和完全分化，例如，似乎就是卡利斯托上的情况。为了探索早期的动态过程，必须从实验室的流变性测量中获得对结冰材料粘度的详细限制。目前，这些数据还不能反映冰雪卫星可能覆盖的各种条件和成分。在这个项目中，将研究冰和冰化合物在压力和温度下的机械性质，这些压力和温度与冰卫星内的所有条件相适应。此外，还将提取许多结冰材料的结构和弹性数据，包括没有高压数据的包合物。应力和应变关系将被用来从在钻石砧座单元中进行的实验中推导出流动规律。这些实验将采用一种新的方法，使用单晶X射线衍射来确定晶格应变。通过研究单晶和多晶组合，将对多晶组合中的局部应力扰动有新的基本见解。冰是开发此类模型的理想模型材料，这些模型对于解释硅酸盐材料的高压流变x射线测量至关重要。冰的结构、静态和动态特性将被整合到木星和土星的大型结冰卫星的内部组成和粘性的模型中。这些模型将被用来研究在吸积过程中和之后导致一些卫星分化为被冰包围的硅酸盐核心的因素，而另一些卫星则主要保持未分化。

Icy materials dominated by H2O but also containing ammonia and methane form the bulk of Neptune and Uranus in addition to the 22 major satellites orbiting the outer planets. These satellites, which are believed to have mainly accreted before the dispersal of the solar nebula, are of particular interest to planetary science as they show a range of diverse geological features including the only extraterrestrial evidence for liquid oceans, active plate tectonics and volcanism. The diverse surface expressions of these satellites reflect differing internal processes active since accretion, which have led, for example, to varying degrees of differentiation of the interiors. A key parameter controlling early differentiation was heat loss from the interior through convection. Only bodies that rapidly established convective regimes would have been able to maintain temperatures low enough to prevent melting and complete differentiation, as appears to be the case on Callisto, for example. In order to explore early dynamic processes, detailed constraints on the viscosity of icy materials must be obtained from laboratory measurements of rheological properties. Currently such data are not available for the range of conditions and compositions likely encompassed by the icy satellites. In this project the mechanical properties of ice and icy compounds at pressures and temperatures compatible with the entire range of conditions within icy satellites will be studied. In addition, structural and elastic data will be extracted for many icy materials including clathrates for which data at high pressures are absent. Stress and strain relations will be used to derive flow laws from experiments performed in the diamond anvil cell. These experiments will employ a novel approach of using single crystal x-ray diffraction to determine lattice strains. By examining single and multiple crystal assemblages, fundamental new insights will be made into local stress perturbations within polycrystalline assemblages. Ices are perfect model materials through which to develop such models, which are vital for interpreting high pressure rheological x-ray measurements on silicate materials. Structural, static and dynamic properties of ices will be integrated into models for the internal composition and viscosity of the large icy satellites of Jupiter and Saturn. These models will be used to examine factors during and subsequent to accretion which lead to some satellites differentiating into silicate cores surrounded by ices, while others remained mainly undifferentiated.