Rotational dynamics and zonal flows of planetary cores

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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.**