The thermal state and internal structure of Mars

The evolution and state of the interior of Mars are studied through the use of theoretically calculated thermal history and density models. These models satisfy the constraints of mean density, moment of inertia, and recent volcanism implied by the Mariner 9 photographs. Invoking melting of an Fe-FeS mixture permits initial core formation within the first billion years. At the present time the core radius ranges from about 1300 to 1800 km, depending on composition, and the core is liquid even if the composition is varied from the eutectic. Large-scale differentiation of the silicates occurs in the last 2 b.y. When the mean density is 3.96 g/cm3, the radius is 3389 km, and the moment of inertia factor is 0.377, the density models indicate high mantle densities near 3.74 g/cm3. Thus an FeO content of about 29% is implied, consistent with the production of a low-viscosity magma. Chemical models of the Martian mantle indicate a composition primarily of olivine with about 56% forsterite. In terms of evolutionary history, Mars is probably intermediate between the moon and the earth, its peak of activity being passed in the last billion years.