The Possible Effect of the Venusian Non-zonal Gravity Field on Rotational Evolution of Venus.

概要

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The periodic change of the rotational rate of the Venus caused by the second sectorial trem of Venusian gravity field was estimated as such that ω=1.6258×10-18 sin 2(λ_??_+3°.24)rad⋅s-2, where λ_??_ is longitude of the Sun in equatorial coordinate system of Venus. Using the mechanical digital model of internal structure of Venus, the secular variation of the rotation rate of Venus caused by its permanent deformation due to the ω above is ωg=-6.3380×10-22 rad⋅s-2, in which, the primordial prograde(anticlockwise) rotation period of Venus T0=15h was used. If the effects of three factors, including the New, the torque of the solar gravitation tide, the Δh3, the zonal component of the angular momentum of the Venusian atmospheric circulation relative to the Venus-fixed axes and the second sectorial term mentioned above, are taken into account, the time of the rotational evolution of Venus from quick anticlockwise rotation to present period clockwise with 243 days is about t=34.6×108 years. However, If both the New and Δh3 are considered only, the time will be t=38.8×108 years. Conclusion: the non-zonal harmonics of Venusian gravity field probably played an important role on rotational evolution of early Venus.
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