Rotational dynamics and zonal flows of planetary cores

行星核心的旋转动力学和纬向流动

• 批准号: RGPIN-2018-05796
• 负责人: Dumberry, Mathieu
• 金额: $ 6.27万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=762447
• 关键词: Rotational; dynamics; zonal; flows; planetary

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.

地球的内部结构是众所周知的，包括一个由液态核(两者主要由铁组成)包围的固体核心，一个厚厚的岩石地幔和一个薄的地壳。然而，对于其他行星和我们的月球来说，情况并非如此。同样，木星和土星的一些卫星被冰壳和次表层海洋覆盖，但人们对这些层的厚度知之甚少。了解行星体的内部结构很重要，因为它与它们是如何进化的有关，进而可以帮助我们了解太阳系是如何形成的。我的研究通过观察行星和卫星的自转来解决这一知识缺口，这是为数不多的使我们能够远程获得其内部结构信息的技术之一。例如，月球在太空中的自转轴方向取决于地球对其非球形形状施加的引力。但是，如果月球有一个大的液核，那么这个方向就会不同。我的研究计划是建立行星自转动力学的模型，并将对其自转轴的预测与观测进行比较，从而提取关于其内部结构的信息。我要培养四名硕士。学生们将把这些模型应用于月球(既包括现在也包括过去的月球)、水星以及木星和土星的冰冻卫星。正如地球海洋中有主要的洋流一样，地球的液核中也发生了大规模的流体运动。这些流动不能直接观测到，但它们创造了地球的磁场。通过分析磁场的变化，我们可以部分重建这些流动的几何形状及其在时间上的波动。我的研究计划的一部分是专注于了解这些核心流程的性质。这对于了解行星的磁场是如何产生的，如何改变极性，以及预测地球磁场的变化是很重要的，这是通信卫星设计的一个关键方面。我的研究计划集中在核心的东西定向流动，即所谓的纬向流。这些流动携带角动量，因此它们的波动也可以从日长的变化中检测到。磁场和日长观测表明，在十年时间上波动的纬向流在旋转轴方向上变化很小(刚性)，但在千年时间尺度上的纬向流是非刚性的。我将培训两名博士生建立模型，研究刚性和非刚性流动的振荡(类似于弹簧悬挂的质量)的模式。通过将我们的模型流与观测结果相匹配，我们将获得关于地核深处磁场的知识。此外，我们还将确定液核顶层分层的厚度和程度，这些属性将为地球的形成和演化提供重要线索。