The iron-snow regime in Fe-FeS cores: a numerical and experimental approach

在地球上，发电机的作用与地核冻结密切相关。有一个坚实的内核，其增长提供了一个浮力通量，驱动发电机。在这种情况下，浮力来源于固体内核和流体外核之间的成分差异。然而，在比地球小的行星体中，这种核心分化过程可能有所不同-铁可能沉淀在核幔边界（CMB）而不是中心，并可能以铁雪的形式落下，并在更深的地方重新熔化。随着时间的推移，化学稳定的沉积区形成，包括整个核心-此时固体内核开始生长。这个系统的动力学以及它是否能产生磁场还没有很好的理解。木卫三，它显示了一个现在的磁偶极子场，是一个候选者，它已经提出了这样的场景。我们计划研究这铁雪政权的数值和实验方法。在数值研究中，我们使用了一个2D/3D热化学对流模型，该模型考虑了铁晶体的结晶和下沉以及液芯相的动力学（对于3D情况，进一步研究Fe雪过程的旋转的影响）。数值计算将通过两个系列的实验来补充：（1）用X射线透视法研究金属合金，（2）用光学技术测量透明的类似物。实验将研究铁雪状态的典型特征。一方面，它们将作为一种工具来验证数值方法，另一方面，它们将产生重要的洞察子过程的铁雪制度，这是无法访问的数值方法，由于其复杂性。

In the Earth, the dynamo action is strongly linked to core freezing. There is a solid inner core, the growth of which provides a buoyancy flux that drives the dynamo. The buoyancy in this case derives from a difference in composition between the solid inner core and the fluid outer core. In planetary bodies smaller than the Earth, however, this core differentiation process may differ – Fe may precipitate at the core-mantle boundary (CMB) rather than in the center and may fall as iron snow and initially remelt with greater depth. A chemical stable sedimentation zone develops that comprises with time the entire core - at that time a solid inner core starts to grow. The dynamics of this system is not well understood and also whether it can generate a magnetic field or not.The Jovian moon Ganymede, which shows a present-day magnetic dipole field, is a candidate for which such a scenario has been suggested. We plan to study this Fe-snow regime with both a numerical and experimental approach. In the numerical study, we use a 2D/3D thermo-chemical convection model that considers crystallization and sinking of iron crystals together with the dynamics of the liquid core phase (for the 3D case the influence of the rotation of the Fe snow process is further studied).The numerical calculations will be complemented by two series of experiments: (1) investigations in metal alloys by means of X-ray radioscopy, and (2) measurements in transparent analogues by optical techniques. The experiments will examine typical features of the iron snow regime. On the one hand they will serve as a tool to validate the numerical approach and on the other hand they will yield important insight into sub-processes of the iron snow regime, which cannot be accessed within the numerical approach due to their complexity.