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

地幔流变学对冰卫星早期分化的影响

• 批准号: 248760695
• 负责人: Dr. Tiziana Boffa Ballaran
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2016-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/248760695?language=en
• 关键词: Influence; Mantle; Rheology; Early; Differentiation

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.

冰质物质主要由H2O组成，但也含有氨和甲烷，形成了海王星和天王星的大部分，以及围绕外行星运行的22颗主要卫星。这些卫星被认为主要是在太阳星云分散之前吸积的，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外星证据。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，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。只有迅速建立对流机制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，木卫四似乎就是这种情况。为了探索早期的动力学过程，详细的约束结冰的材料的粘度必须从实验室测量的流变特性。目前，这些数据还不适用于结冰卫星可能包含的条件和成分范围。在该项目中，将研究冰和冰化合物在与冰卫星内各种条件相适应的压力和温度下的机械特性。此外，将提取许多冰材料的结构和弹性数据，包括在高压下缺乏数据的笼形物。应力和应变关系将被用来从金刚石压砧单元中进行的实验中推导出流动定律。这些实验将采用一种使用单晶X射线衍射来确定晶格应变的新方法。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产生根本性的新认识。冰是开发此类模型的完美模型材料，这对于解释硅酸盐材料的高压流变学X射线测量至关重要。冰的结构、静态和动态特性将被纳入木星和土星大型冰卫星的内部成分和粘性模型。这些模型将被用来检查吸积过程中和之后的因素，导致一些卫星分化成被冰包围的硅酸盐核，而其他卫星则主要是未分化的。