Mercury: Internal structure and thermal evolution |
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| Authors: | Robert W Siegfried Sean C Solomon |
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| Institution: | Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA |
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| Abstract: | Astronomical observations and cosmochemical calculations suggest that the planet Mercury may be composed of materials which condensed at relatively high temperatures in the primitive solar nebula and may have a basaltic crust similar to parts of the moon. These findings, plus the long standing inference that Mercury is much richer in metallic iron than the other terrestrial planets, provide important constraints which we apply to models of the thermal evolution and density structure of the planet. The thermal history calculations include explicitly the differing thermal properties of iron and silicates and account for core segregation, melting and differentiation of heat sources, and simulated convection during melting. If the U and Th abundances of Mercury are taken from the cosmochemical model of Lewis, then the planet would have fully differentiated a metal core from the silicate mantle for all likely initial temperature distributions and heat transfer properties. Density distributions for the planet are calculated from the mean density and estimates of the present-day temperature. For the fully differentiated model, the moment of inertia C/MR2 is 0.325 (J2=0.302×10?6). For models with lower heat source abundances, the planet may not yet have differentiated. The density profiles for such models give C/MR2=0.394 (J2=0.487×10?6). These results should be useful for preliminary interpretation of the Mariner 10 measurements of Mercury's gravitational field. |
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