The motion of Mars' pole. I - Rigid body precession and nutation

Abstract

Abstract : Differences between the observed forced nutation component amplitudes of the Earth and predicted nutation amplitudes for a rigid Earth are a result of differences between the theoretical rigid structure of the Earth used in older models and the actual elastic Earth with a liquid core. However, except for the period of the Chandler wobble, the observations of the motion of the Earth's pole were not accurate enough to observe the effects of the elastic, liquid core Earth until the last 30 years. In more recent works, such as those by Wahr (198la,b), the nutation resulting from an elastic, liquid core Earth are modeled as perturbations of the rigid Earth model nutation. This is the approach adopted for the 1980 IAU Theory of Nutation to determine the amplitude of the various nutational elements (Kaplan 1981). These perturbations result in modifications to the nutation amplitudes for the Earth from about 1% to 0.01% of the theoretical rigid nutation amplitudes or about O.019 for the largest term in the series. Since the l950s the improvement in the measurement of the motion of the Earth's pole have made its observation a powerful probe of the structure of the Earth.