Internal Constitution of Mars

Abstract

THERE are three basic hypotheses to account for the low density of Mars compared with the Earth. Ramsay1 and Bullen2 suggest that both planets have the same overall chemical composition, but that differential self-compression in their respective gravitational fields combined with phase changes lead to differing densities. This hypothesis implies that the Earth's core represents a phase transformation from the non-metallic state of the mantle to a denser metallic state. Jeffreys3 and Urey4 assume that Mars and Earth consist chiefly of silicates and metallic iron. The composition of each of these phases is similar in both planets but Mars contains a smaller proportion of metallic iron. A third hypothesis has been proposed by Ringwood5,6, in which the relative abundances of the common metals, Fe, Mg, Al, Si and so on, are similar in Mars, Earth and Venus, and also similar to abundances in the Sun and in Type 1 carbonaceous chondrites. Differences in density between the planets are caused by differences in the amount of oxygen present, Mars being more oxidized than the Earth and Venus representing an intermediate state. Additional hypotheses on the constitution of Mars have been proposed7–9 but these are essentially combinations of the second and third hypotheses mentioned above, and will not be considered further.

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RINGWOOD, A., CLARK, S. Internal Constitution of Mars. Nature 234, 89–92 (1971). https://doi.org/10.1038/234089a0

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