Sulfur can also exist in Mars' core. If it does, then the core may be quite large. Mars does not have a significant magnetic field, so that leaves to the conclusion that Mars's core is probably solid. Mars doesn't have plate tectonics, a crust made up of seperate sections that move about and sometimes crash into each other.
Since Mars is much smaller than Earth, it cooled quickly after formation and the crust thickened, forming one solid piece and eliminating any possibility plate tectonics, as is seen on Earth. Martian crust isn't broken into seperate plates, so Mars' liquid mantle has created the surface of the planet.