Composition of Mars constrained using geophysical observations and mineral physics modeling

摘要

We use the total mass, possible core radius and the observed mean moment of inertia factor of Mars to constrain mineralogical and compositional structures of Mars. We adopt a liquid Fe-S system for the Martian core and construct density models of the interior of Mars for a series of mantle compositions, core compositions and temperature profiles. The moment of inertia factor of the planet is then calculated and compared to the observation to place constraints on Mars composition. Based on the independent constraints of total mass, possible core radius of 1630-1830km, and the mean moment of inertia factor (0.3645 ± 0.0005) of Mars, we find that Fe content in the Martian mantle is between 9.9 and 11.9mol%, Al content in the Martian mantle smaller than 1.5mol%, S content in the Martian core between 10.6 and 14.9wt%. The inferred Fe content in the bulk Mars lies between 27.3 and 32.0wt%, and the inferred Fe/Si ratio in Mars between 1.55 and 1.95, within a range too broad to make a conclusion whether Mars has the same nonvolatile bulk composition as that of CI chondrite. We also conclude that no perovskite layer exists in the bottom of the Martian mantle. Based on the inferred density models, we estimate the flattening factor and _(J2) gravitational potential related to the hydrostatic figure of the rotating Mars to be (5.0304 ± 0.0098) × ~(10 - 3) and (1.8151 ± 0.0065) × ~(10 - 3), respectively. We also discuss implications of these compositional models to the understanding of formation and evolution of the planet.