Theoretical study on mantle overturn processes in the moon and small rocky planets.

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Theoretical and numerical studies on the evolution of the interiors of the Moon and small rocky planets were performed on the basis of the consideration about the variety of raw materials of these bodies by using a model of proto-planetary disk. A series of cumulate rock layers, formed in the early Moon due to cooling and solidification of a magma ocean, should have overturned toward stable structure. During the overturn process, Mg-rich olivine cumulate likely becomes to melt again, which is consistent with the exposure of Mg-rich mafic minerals on the lunar far-side. The present moment of inertia factor of the Moon is explained by the density profile after the completion of overturn. Recent spacecraft data shows that Mercury has a significantly reduced composition enriched in sulfur as well as E-chondrites, which is consistent with our disk model, and also has a thin silicate mantle with thickness less than about 400 km. We performed thermal history simulations considering such a new structure. It is suggested that the liquid core of Mercury is thermally convective until present, allowing dynamo action producing the intrinsic magnetic field of Mercury.