Low hydrogen contents in the cores of terrestrial planets

Vincent Clesi (1) , Mohamed Ali M.A. Bouhifd (1) , Nathalie Bolfan-Casanova (1) , Geeth Manthilake (1) , Federica Schiavi (1) , Caroline Raepsaet (2) , Helene Bureau (3) , Hicham Khodja (2) , Denis Andrault (1)

1 LMV - Laboratoire Magmas et Volcans
2 LEEL - UMR 3685 - Laboratoire d'Etudes des Eléments Légers
3 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

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.

Domains: Chemical Sciences; Material chemistry; Sciences of the Universe [physics]; Earth Sciences; Geochemistry

Vincent Clesi, Mohamed Ali M.A. Bouhifd, Nathalie Bolfan-Casanova, Geeth Manthilake, Federica Schiavi, et al.. Low hydrogen contents in the cores of terrestrial planets. Science Advances , 2018, 4 (3), pp.e1701876. ⟨10.1126/sciadv.1701876⟩. ⟨cea-01736955⟩