Low hydrogen contents in the cores of terrestrial planets

• Published in: Science advances 2018-03, Vol.4 (3), p.e1701876-e1701876
• Main Authors: Clesi, Vincent, Bouhifd, Mohamed Ali, Bolfan-Casanova, Nathalie, Manthilake, Geeth, Schiavi, Federica, Raepsaet, Caroline, Bureau, Hélène, Khodja, Hicham, Andrault, Denis
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Earth Sciences; Geochemistry; Material chemistry; Physical Sciences; Planetary Science; SciAdv r-articles; Sciences of the Universe
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.1701876

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 , 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.