Low hydrogen contents in the cores of terrestrial planets

Abstract : Hydrogen has been thought to be an important light element in Earth's core due to possible siderophile behavior during core-mantle segregation. We reproduced planetary differentiation conditions using hydrogen contents of 450 to 1500 parts per million (ppm) in the silicate phase, pressures of 5 to 20 GPa, oxygen fugacity varying within IW-3.7 and IW-0.2 (0.2 to 3.7 log units lower than iron-wüstite buffer), and Fe alloys typical of planetary cores. We report hydrogen metal-silicate partition coefficients of ~2 × 10$^{−1}$ , up to two orders of magnitude lower than reported previously , and indicative of lithophile behavior. Our results imply H contents of ~60 ppm in the Earth and Martian cores. A simple water budget suggests that 90% of the water initially present in planetary building blocks was lost during planetary accretion. The retained water segregated preferentially into planetary mantles.
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Vincent Clesi, Mohamed Bouhifd, Nathalie Bolfan-Casanova, Geeth Manthilake, Federica Schiavi, et al.. Low hydrogen contents in the cores of terrestrial planets. Science Advances, American Association for the Advancement of Science, 2018, 4 (3), pp.e1701876. ⟨http://advances.sciencemag.org/content/4/3/e1701876⟩. ⟨10.1126/sciadv.1701876⟩. ⟨cea-01736955⟩

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