Rotational dynamics and zonal flows of planetary cores

地球的内部结构是众所周知的，包括一个固体内核被一个液体内核包围（两者主要由铁组成），一个厚厚的岩石地幔和一个薄地壳。然而，其他行星和我们的月球却不是这样。同样，木星和土星的一些卫星被冰壳和地下海洋覆盖，但对这些层的厚度知之甚少。了解行星体的内部结构是很重要的，因为它与它们是如何进化的有关，反过来，可以帮助我们了解太阳系是如何形成的。我的研究通过对行星和卫星旋转的观测来解决这一知识空白，这是为数不多的可以让我们远程获取其内部结构信息的技术之一。例如，月球在太空中的旋转轴方向取决于地球对其非球形施加的引力。但如果月球有一个大的流体核心，这个方向就会不同。我的研究计划是建立行星的旋转动力学模型，并将其旋转轴的预测与观测结果进行比较，从而提取其内部结构的信息。我将培养四名硕士学生，他们将把这些模型应用于月球（包括现在的和过去的）、水星以及木星和土星的冰冷卫星。就像地球海洋中有主要的洋流一样，大规模的流体运动也发生在地球的液体内核中。这些气流不能直接观察到，但它们负责创造地球磁场。通过分析磁场的变化，我们可以部分地重建这些流的几何形状及其随时间的波动。我的研究计划的一部分集中在理解这些核心流的本质。这对于了解行星磁场是如何产生的、如何改变极性以及预测地球磁场的变化是很重要的，而地球磁场的变化是设计通信卫星的一个关键方面。我的研究计划集中在地核中东西方向的流动，也就是所谓的地带性流动。这些气流带有角动量，所以它们的波动也可以在一天长度的变化中检测到。磁场和日长观测表明，在年代际上波动的纬向流在旋转轴方向上变化不大（刚性），但在千年时间尺度上的纬向流是非刚性的。我将训练两名博士生建立模型来研究刚性和非刚性流动的振荡模式（类似于弹簧悬挂的质量）。通过将我们的模型流与观测相匹配，我们将获得地核深处磁场的知识。此外，我们将确定流体岩心顶层的厚度和分层程度，这些属性将为地球的形成和演化提供重要线索。

The interior structure of Earth is well known, comprising a solid inner core surrounded by a liquid core (both dominantly composed of Iron), a thick rocky mantle and a thin crust. However, this is not the case for other planets and our Moon. Likewise, some moons of Jupiter and Saturn are covered by an ice shell and subsurface ocean, but little is known about the thicknesses of these layers. Knowing the interior structure of planetary bodies is important because it is linked to how they have evolved and, in turn, can help us understand how the solar system formed.My research addresses this gap in knowledge by using observations on the rotation of planets and moons, one of the very few techniques available that allows us to gain information on their interior structure remotely. The orientation of the rotation axis of the Moon in space, for example, depends on the gravitational force exerted by Earth on its non-spherical shape. But this orientation would be different if the Moon were to have a large fluid core. My research plan is to build models of the rotation dynamics of planets and to compare predictions of their spin axis with observations and thus extract information on their interior structure. I will train four M.Sc. students who will apply these models to the Moon (both at present but also in its past), Mercury and the icy moons of Jupiter and Saturn.Just as there are major currents in Earth's oceans, large scale fluid motions also take place in the Earth's liquid core. These flows cannot be observed directly, but they are responsible for creating the Earth's magnetic field. By analyzing changes in the magnetic field, we can partly reconstruct the geometry of these flows and their fluctuations in time. A part of my research program is focused on understanding the nature of these core flows. This is important in order to understand how the magnetic field of planets are generated, can change polarity, and to forecast changes in Earth's magnetic field, a crucial aspect for the design of communication satellites.My research plan is centered on east-west directed flows in the core, so-called zonal flows. These flows carry angular momentum so their fluctuations can also be detected in the changes in the length-of-day. Magnetic and length-of-day observations suggest that zonal flows fluctuating on decadal times have little variations in the direction of the rotation axis (rigid), however zonal flows at millennial timescale are non-rigid. I will train two Ph.D. students to build models to study the modes of oscillations (akin to a mass suspended by a spring) of rigid and non-rigid flows. By matching our model flows with observations, we will gain knowledge on the magnetic field deep inside the core. Furthermore, we will determine the thickness and degree of stratification in the top layer of the fluid core, attributes which will provide important clues on the formation and evolution of the Earth.