Secular Obliquity Variations Due to Climate Friction on Mars: Re-examination in Influence of Martian Internal Viscosity Structure

Secular obliquity variations due to climate friction on Mars are calculated. Martian interior is considered to be a three-layered structure. A viscosity of each layer is treated as a parameter. The results give knowledge as follows. First, under an internal structure with a crust of ``finite viscosity'' and/or a ``solid'' core, the effect of the climate friction becomes greater than that concluded by previous research. Second, under an internal structure with a mantle of ``heterogeneous viscosity'' the possibility of the great effect of the climate friction becomes stronger than that concluded by previous research.