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Carbon stability in planetary mantles has been studied by numerous authors because it is thought to be the source of C-bearing atmospheres and of C-rich lavas observed at the planetary surface. In the Earth, carbonaceous peridotites and eclogites compositions have been experimentally studied at mantle conditions (1) (2) (3). (4) showed that the fO2 variations observed in martian meteorites can be explained by polybaric graphite-CO-CO2 equilibria in the Martian mantle. Based on thermodynamic calculations (4) and (5) inferred that the stable form of carbon in the source regions of the Martian basalts should be graphite (and/or diamond), and equilibrium with melts would be a source of CO2 for the martian atmosphere. Considering the high content of iron in the Martian mantle (approx.18.0 wt% FeO; (6)), compared to Earth s mantle (8.0 wt% FeO; (7)) Fe/C redox interactions should be studied in more detail.