Carbon is extremely abundant in the solar system (10 × Si, 20 × S) in Cl carbonaceous chondrites (3.2 wt%) and it dissolves readily in liquid Fe at low pressures (4.3 wt% at 1420 K). Despite these properties it is rarely considered a potential light element in the Fe-rich core, because it is volatile, even at low temperatures as CO. In this paper I show that carbon volatility is a strongly pressure-dependent phenomenon and that it applies during condensation from a solar gas ( ∼ 10-3 atm), but not at the pressures and temperatures generated during planetary accretion and differentiation (0.01-5 GPa). Thus, impact heating and degassing of the protoearth should have led to an Fe-rich melt with around 2-4 wt% carbon, compared to the 0.01-0.6 wt% in iron meteorites and 0.3-3 ppm C predicted to be present in Fe condensed from the solar gas. Experiments (to 9 GPa) and thermodynamic calculations on the systems FeC and FeCS show that carbon solubility in Fe melt increases slightly with pressure but that carbon could not conceivably constitute more than half the light element content of the core. The addition of even very small amounts of carbon (
