火星内部構造の高温高圧実験による推定

Abstract

A model of the structure in the Martian interior was presented on the basis of the high pressure and temperature experiments on the homogeneous Martian mantle model composition of Morgan and Anders (1979). The sequence of phase assemblages with increasing depth in the Martian interior is summarized as follows: olivine+pyroxene+plagioclase (+minor phases) in the mantle at the depths shallower than 230km; olivine+pyroxene+garnet from 230 to 1, 280km; garnet+β-spinel and/or γ-spinel ((Mg, Fe)2, SiO4, )+magnesiowustite in the Martian transition zone from 1, 280 to 1, 800km; garnet+Mg-perovskite+Ca-perovskite+magnesiowustite in the Martian lower mantle from 1, 800 to 2, 020km. The core-mantle boundary is calculated on the basis of the total mass of Mars and the density profile of the mantle and core. This model satisfies the observed geophysical data of the mean radius and mean density. The moment of inertia factor of this model (0.363) is close to the observed value (0.365). Using the Martian basic data, such as the mean density, the total mass, and the density profile of Mars estimated on the basis of the results of the high pressure and temperature experiments, the realistic value of the total iron content and the moment of inertia factor have been estimated. The iron content of Mars which satisfies the mean density and the radius of Mars ranges from 19 wt. % to 27 wt. % with the temperature ambiguities of±200°C. This value is smaller than that of the bulk Earth. The moment of inertia factor of the Mars, which satisfies the mineralogical constraints of the high pressure phase transitions together with the observed data on the mean density and the radius of Mars, ranges from 0.353 to 0.38.