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，包括一个固体内核，周围是液体（既主要由铁组成），厚岩石的地幔和薄皮。但是，其他行星和我们的月亮并非如此。 同样，一些木星和土星的月亮被冰壳和地下海洋覆盖，但对这些层的厚度知之甚少。 了解行星体的室内结构很重要，因为它与它们的发展方式相关联，进而可以帮助我们了解太阳系的形成方式。我的研究通过使用对行星和月亮的旋转观察来解决知识的差距，这是对我们少数几个技术的旋转，使我们能够在其室内结构上获得信息。 例如，太空中月球旋转轴的方向取决于地球在其非球形形状上施加的重力。但是，如果月球具有大的流体核心，则这种方向将有所不同。我的研究计划是构建行星旋转动力学的模型，并将其旋转轴的预测与观测值进行比较，从而提取有关其内部结构的信息。 我将训练四硕士将这些模型应用于月球的学生（目前和过去），水星和木星和土星的冰冷月亮。正如地球海洋中有主要水流一样，大规模的流体运动也发生在地球液体中。无法直接观察到这些流，但是它们负责创建地球的磁场。 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及时的波动。 我的研究计划的一部分侧重于理解这些核心流的性质。 这对于了解行星的磁场是如何产生，可以改变极性的，并预测地球磁场的变化很重要，这是通信卫星设计的关键方面。 这些流带有角动量，因此在一天的变化中也可以检测到它们的波动。磁性和长度的观测表明，衰老时期的纬向流动在旋转轴的方向上几乎没有变化（刚性），但是在千年时间尺度上的区域流量是非rigid的。 我将培训两位博士学位。学生建立模型来研究刚性和非刚性流动的振荡模式（类似于春季悬挂的质量）。通过将模型流与观测值匹配，我们将在核心内部的磁场上获得知识。 此外，我们将确定流体核心顶层的厚度和分层程度，这些属性将提供有关地球形成和演变的重要线索。