Abstract
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 a "heterogeneous viscosity", the possibility of the great effect of the climate friction becomes stronger than that concluded by previous research.
