Periodic Reporting for period 1 - HotCores (High Temperature Dynamics of Metals and the Earth’s Solid Inner Core)
Reporting period: 2022-12-01 to 2025-05-31
As the Earth cools, solid iron (Fe) crystallizes from the outer core to form the inner core, a form of mini-planet with a radius of 1220 km at the center of the Earth. The Earth's inner core affects our life at the surface; its growth provides a major source of energy for sustaining the Earth’s magnetic field. One may view the inner core as a freezing ball of Fe floating at the center of the liquid outer core, but seismic exploration reveal structures of increasing complexity, raising fundamental questions on the history and internal dynamics of this deep region of the planet.
Geophysical observations unearth the inner-core as it is today. Understanding the history of the inner-core and its effect on the global Earth dynamics, however, requires a reconstruction based on today’s observations and knowledge of the physical properties of the inner-core Fe alloy, how they could affect inner-core dynamics, and their relation with present-day geophysical observables. There are significant knowledge gaps and outdated principles regarding the underlying physical properties of the inner-core Fe alloy. In particular, temperature is close to melting, and the inner-core might even be partially molten. How does temperature affect of the mechanical properties of the inner-core Fe alloy? What is the effect of temperature and partial melting on seismic observables such as wave travel time and attenuation? This is poorly known, and it hinders our interpretation capability of the ever-growing body of geophysical observations.
In HotCores, advanced high pressure and/or high temperature experiments will be performed on Fe alloys and analogues. We are reenacting key events of the history of the inner-core in the laboratory, as Fe crystallizes at the inner and outer-core boundary, as the inner-core grows and dynamically evolves to its present state, and as we see it today through the lenses of geophysical exploration. What is the structure and dynamics of the inner-core? How will it evolve in the future? HotCores aims at providing the mineralogical foundation that will help to solve these mysteries.
Geophysical observations unearth the inner-core as it is today. Understanding the history of the inner-core and its effect on the global Earth dynamics, however, requires a reconstruction based on today’s observations and knowledge of the physical properties of the inner-core Fe alloy, how they could affect inner-core dynamics, and their relation with present-day geophysical observables. There are significant knowledge gaps and outdated principles regarding the underlying physical properties of the inner-core Fe alloy. In particular, temperature is close to melting, and the inner-core might even be partially molten. How does temperature affect of the mechanical properties of the inner-core Fe alloy? What is the effect of temperature and partial melting on seismic observables such as wave travel time and attenuation? This is poorly known, and it hinders our interpretation capability of the ever-growing body of geophysical observations.
In HotCores, advanced high pressure and/or high temperature experiments will be performed on Fe alloys and analogues. We are reenacting key events of the history of the inner-core in the laboratory, as Fe crystallizes at the inner and outer-core boundary, as the inner-core grows and dynamically evolves to its present state, and as we see it today through the lenses of geophysical exploration. What is the structure and dynamics of the inner-core? How will it evolve in the future? HotCores aims at providing the mineralogical foundation that will help to solve these mysteries.
The project is divided into several work-packages, addressing targeting key events affecting the inner-core Fe-alloy and leading to observations of the inner-core as we can see it today. Understanding the physical characteristics of metals under extreme pressure and temperature conditions is at the heart of all three, working either on iron-alloys themselves, or other metal analogues to constrain our physical models.
A new class of experiments at the European XFEL, capable of producing ultrashort and extremely intense X-ray flashes at a rate of 27,000 times per second, is the basis for the project's first package. The facility is coupled with static high pressure devices, such as diamond anvil cells, to reach the conditions of the Earth’s inner core. It is also used in conjunction with an intense optical laser, Dipole-100X, to produce temporally shaped pulses and shock waves into our samples. These allow to test and explore the physical properties of iron and iron alloys in conditions that could not be reached previously, which we are currently testing and exploring in the framework of the project.
These experiments are complimented with laboratory and synchrotron-based experiments addressing finer questions regarding iron alloys in the Earth inner-core. In particular, we wish to understand how the iron alloy can affect geophysical observables such as seismic wave velocities and anisotropy, seismic attenuation, and visco-elastic relaxation. To do so, we are in the process of developing new devices to work at conditions relevant to the Earth’s inner core. One route relies on experiments high temperature, close to melting, on metal analogues to develop physical models to be used in extrapolations. The other route uses combined conditions of pressures and temperatures. This work is ongoing and will be described more thoroughly as the project moves forward.
A new class of experiments at the European XFEL, capable of producing ultrashort and extremely intense X-ray flashes at a rate of 27,000 times per second, is the basis for the project's first package. The facility is coupled with static high pressure devices, such as diamond anvil cells, to reach the conditions of the Earth’s inner core. It is also used in conjunction with an intense optical laser, Dipole-100X, to produce temporally shaped pulses and shock waves into our samples. These allow to test and explore the physical properties of iron and iron alloys in conditions that could not be reached previously, which we are currently testing and exploring in the framework of the project.
These experiments are complimented with laboratory and synchrotron-based experiments addressing finer questions regarding iron alloys in the Earth inner-core. In particular, we wish to understand how the iron alloy can affect geophysical observables such as seismic wave velocities and anisotropy, seismic attenuation, and visco-elastic relaxation. To do so, we are in the process of developing new devices to work at conditions relevant to the Earth’s inner core. One route relies on experiments high temperature, close to melting, on metal analogues to develop physical models to be used in extrapolations. The other route uses combined conditions of pressures and temperatures. This work is ongoing and will be described more thoroughly as the project moves forward.
Research takes times! Two year into the project, we have laid out the work procedures, purchased and installed our instruments, and identified or hired most of the team members. This section will be filled as the project moves forward.