History of the early solar system as recorded by planetesimal metallic cores – IronMet

The origin and incorporation of volatile elements like nitrogen (N) and carbon (C) into planets are not well understood. This is despite the critical role they play in the geological evolution of planets and the emergence of life. Planets formed by accretion of planetesimals, the first planetary bodies of the solar system, which incorporated volatiles from the solar nebula during their formation. It is therefore critical to better understand the mechanism of incorporation of volatiles into planetesimal interiors before tackling the question of their effect on the evolution of planets. Most iron meteorites are remnant pieces of metallic cores of the earliest-formed planetesimals. Because N and C can partition into the core, iron meteorites are most appropriate to study their primordial abundances and isotopic compositions in planetesimals.

The liquid metallic cores of the same planetesimals may have generated magnetic fields by dynamo effect. Although accumulating evidence from meteorite paleomagnetic studies suggest that planetesimal magnetic fields may have been common, the processes generating and sustaining a dynamo in such bodies are largely unknown. Iron meteorites contain a ferromagnetic mineral called tetrataenite, that forms tens of million years after planetesimal formation. The paleomagnetic record of this mineral, which reflects the intensity of the ancient magnetizing field, is our only source of information regarding the late magnetic activity of planetesimals. However, the reliability of our interpretations of these records crucially depends on our understanding of the magnetization acquisition mechanism for tetrataenite, which is currently poorly understood. It is crucial to understand this process to achieve a comprehensive understanding of planetesimal dynamo activity.
The project IronMet focuses on these major challenges and has two overarching objectives: understand the mechanism of incorporation into iron meteorites of N and C, and understand the mechanism by which tetrataenite is magnetized. We propose an innovative combination of ultra-high-resolution techniques to achieve these objectives through a nanoscale approach. We will use atom probe tomography, nanoscale secondary ion mass spectrometry and X-ray photoemission electron microscopy to test critical hypotheses regarding the distribution and mobility of N and C in iron meteorites, the magnetization acquisition mechanism in tetrataenite, and the possible influence of these volatiles on this mechanism.
IronMet combines the partners’ expertise in planetology and material sciences down to the atomic level. Interdisciplinary in essence, it will have major and timely implications. First, questions related to the incorporation of life-essential volatiles into terrestrial planets in the early solar system are particularly sensitive. Our results will contribute to shedding light on these processes and help identify potential biases in the interpretation of bulk meteorite data. Second, paleomagnetic records of tetrataenite-bearing meteorites are essential to understand the magnetic and thermal history of planetesimals. Our results will largely increase the reliability of the interpretations of these records. Third, iron meteorites are increasingly recognized as the new frontier for the study of the earliest planetary environment and processes. IronMet will contribute to forming a new generation of iron meteorite scientists, taking this discipline to a new level following the recent loss of pioneers of the field. Finally, IronMet will contribute to the national effort aimed at making France a major actor in the development of atom probe tomography and its applications to geosciences.
The three partners are internationally recognized for their expertise in meteoritics, magnetism, isotope geochemistry and material science. They combine the complementary technical, analytical and thematic expertise needed to achieve the objectives of IronMet.