¹Fabrice Gaillard, ²Yves Marrocchi, ¹Gregory Rogerie, ³Mohamed A. Bouhif, ¹Camille Bernard, ⁴Mathieu Roskosz
Earth and Planetary Science Letters, 692, 120245 Link to Article [DOI: 10.1016/j.epsl.2026.120245]

¹Institut Des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, 1a Rue de la Férollerie 2, Orléans, 45071 CEDEX, France
²Université de Lorraine, CNRS, CRPG, Nancy, F-54000, France
³Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, F-63000, France
⁴IMPMC, MNHN, CNRS, UMR 7590, Muséum National d’Histoire Naturelle, Sorbonne Universités, CP 52, 57 rue Cuvier, Paris, F-75231, France
Copyright Elsevier

The Mercury-Venus-Earth-Mars-Vesta planetary suite exhibits large variations in oxidation state as defined by the Fe to FeO ratio (i.e. core to silicate ratio), with increasingly oxygen-depleted bodies toward the centre of the solar system. As undifferentiated materials (i.e., chondrites) likely display a similar heliocentric FeO-gradient, planetary and chondritic oxidation states should be related in this respect. We develop an approach wherein, the equilibrium oxygen redistribution during gas – silicate melt – molten metal alloy during differentiation is resolved for bodies of various compositions and sizes. As a case study, three chondritic end-members were considered: enstatite, ordinary, and carbonaceous. A broad range of planetary oxidation states are obtained that encompass the above-mentioned planetary suite. The oxidation state during the growth of small bodies (<2000 km in radius) of constant bulk composition is affected by metal-vapour carbon redistribution, whereas on larger bodies, the incorporation of hydrogen, oxygen and silicon in the core prevails, causing the convergence toward a putative universal magma ocean FeO content. A dual regime is observed for the water content in the silicate magma ocean, which increases up to a planetary radius of ∼3000 km, whereas in larger bodies, hydrogen incorporation into the core brings about dehydration of the complementary silicate mantles. The accretion of ordinary chondrites perfectly matches the oxidation state of Mars and produces a core with C-H-S-N contents matching the Martian core density as suggested by the Insight missions. Finally, Vesta’s oxidation state seemingly requires an H2O-rich oxidizing component during the formation of planetesimals.