Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 563, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2021.116884
Keywords
liquid iron-sulfur alloys; density; thermal expansion; high pressure and temperature; telluric planetary cores; crystallizationregime
Categories
Funding
- ANR [2010-JCJC-60401]
- Region Ile de France grant SESAME [N.I-07593/R]
- INSU-CNRS
- Institute de Physique (INP)-CNRS
- University Pierre et Marie Curie-Paris 6
- French National Research Agency (ANR) [ANR-07-BLAN-0124-01]
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation Programme [724690]
- Belgian PRODEX program
- Belgian Federal Science Policy Office
- French Government Laboratory of Excellence initiative [ANR-10-LABX0006]
- Region Auvergne
- European Regional Development Fund [469]
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The local structure and density of liquid Fe-S alloys at high pressure were determined in situ by X-ray diffraction experiments. It was found that top-down solidification is the dominant scenario for Fe-S cores of asteroids and small planetesimals, while bottom-up growth of the inner core may occur in S-poor cases.
Local structure and density of liquid Fe-S alloys at high pressure have been determined in situ by combined angle and energy dispersive X-ray diffraction experiments in a multi-anvil apparatus, covering a large temperature and compositional range. Precise density measurements collected for increasing temperature allowed us to directly derive the thermal expansion coefficients for liquid Fe-S alloys as a function of composition. In turn, thermal expansion has been used to refine thermodynamic models and to address the crystallization regime of telluric planetary cores by comparing the adiabatic temperature gradient and the slope of the liquidus in the Fe-FeS system. For Fe-S cores of asteroids and small planetesimals, top-down solidification is the dominant scenario as the compositional domain for which the slope of the liquidus is greater than the adiabatic gradient is limited to a narrow portion on the Fe-rich side. However, bottom-up growth of the inner core is expected for S-poor cases, with this compositional domain expanding to more S-rich compositions with increasing pressure (size of the planetary body). In particular, bottom-up crystallization cannot be excluded for the Moon and Ganymede. (C) 2021 Elsevier B.V. All rights reserved.
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