Revealing the unknown planet within the Earth

Principal investigator (PI): Sébastien Merkel

PI's host institution : Université de Lille
Hosting laboratory : Unité Matériaux et Transformations
Duration: 60 months

ERC Advanced Grant 2021
Project ID: 101054994

Starting date: December 2022

The Earth’s inner-core (IC) is 1220 km radius planet within the Earth, made of solid iron (Fe) crystallizing from the outer core (OC) as the Earth cools down. The IC affects our life at the surface; its growth provides a major source of energy for maintaining the Earth’s magnetic field. One may view the IC as a freezing ball of Fe floating at the center of the OC, but seismic exploration reveal structures of increasing complexity, raising fundamental questions on the history and internal dynamics of the IC.

Geophysical observations unearth the IC as it is today. Understanding the history of the IC and the effect of the IC on the global Earth dynamics, however, requires a reconstruction based on today’s observations and knowledge of the physical properties of the IC Fe alloy, how they could affect IC dynamics, and their relation with present-day geophysical observables. There are significant knowledge gaps and outdated principles regarding the underlying physical properties of the IC Fe alloy.

The IC temperature is close to melting, and the IC might even be partially molten. How does temperature affect of the mechanical properties of the IC 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 propose to reenact key events of the history of the IC in the laboratory, as Fe crystallizes at the inner-outer-core boundary, as the IC 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 IC? How will the IC evolve in the future? HotCores aims at providing the mineralogical foundation that will help solving these mysteries.

HotCores: a five-year research project funded by the European Research Council (ERC) Advanced Grant program to reveal the unknown planet within the Earth