Fig. 3
From: Mars core structure—concise review and anticipated insights from InSight
Melting relations in the Fe-FeS system in the pressure and compositional range suitable for Mars’ core. Isotherms show temperature (K) of appearance of first solid in the system depending on the composition and pressure. Thick lines delimit fields of first crystallizing solid: Fe, FeS, and Fe 3−x S 2 (Fe-FeS eutectic on left and incongruent melting of Fe 3−x S 2 on right). Gray box shows likely pressure and compositional range for core. Intersection of box with isotherms shows that for any crystallization of solids in the inner core, temperatures must be less than ∼1650 K. First solids to crystallize will be Fe 3−x S 2 if in S-rich compositions and will be Fe if S-poor. When eutectic reached, crystallizing solids will vary depending on subsolidus phase diagram but will ultimately be Fe + Fe 3S or Fe 3−x S 2+Fe 3S (Fei et al. 2000)