Zhao, B. ; Morard, G. ; Boulard, E. ; Boccato, S. ; Siersch, N. C. ; Rivoldini, A. ; Guignot, N. ; Henry, L. ; King, A. ; Zurkowski, C. ; Fei, Y. ; Antonangeli, D.

Poster presented at AGU 2023 San Fransisco on 2023-12-14

Abstract: The Fe-FeS binary is largely seen as the archetypal system to model the properties of the core of small to medium-sized telluric bodies. Noteworthy, while at the low pressures characteristic of the Moon the Fe-FeS is a simple binary eutectic, at the conditions relevant for planets such as such as Mercury, or satellite such as Ganymede, Io, and Europa, the Fe-S phase diagram is quite complex, with intermediate compounds of narrow stability field that incongruently melt. Fe-FeS compounds have thus been studied in the range 11-15 GPa, between room temperature to solidus, using in situ X-ray diffraction to assess stability and equation of state of the Fe3S2 solid phase. The stability field of FeS and Fe3S2 indicates that Fe3S2 is a potential crystallization product of S-rich telluric bodies and should be used as the end-member phase to model the properties of telluric planetary cores in the 12-20 GPa range together with, respectively, Fe or FeS depending on whether the S content is less than or grater than 27wt%. However, Fe3S2 is not expected to form in the cores of Europa, Io, or Ganymede, as they are too small, or in Mercury, as most likely too low in S. As C is another light element potentially present at a few wt% in the core of terrestrial planets, it is important to understand its effects on the properties of Fe-S alloys. Therefore, the local structure and density of ternary Fe-C-S liquid alloys have been studied in-situ by the combination of X-ray diffraction and absorption measurements between 1 and 5 GPa and 1600 to 1900 K. Obtained results allowed us to develop a thermodynamic model of the liquid Fe-C-S system that is used to correlate the densities proposed in recent models of the Moon with the S and C content within its core.

Note: MR43C-0105
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Funding: 3PORODPLANINT/3PORODPLANINT/3PORODPLANINT