Motion of Mars' Pole II. The Effect of an Elastic Mantle and a Liquid Core.

摘要

A first-order approximation of the effects of an elastic mantle and liquid core on the motion of Mars' pole are explored. The effect on Mars' Chandler wobble (Eulerian free nutation) is much less dependent on Mars' structure than the Earth's Chandler wobble depends on the Earth's structure. The period of the liquid core free-core nutation (FCN), however, is found to be very sensitive to the mean core radius; if the FCN period is known with an uncertainty of 2 days, then the mean core radius can be inferred with an uncertainty of only 6 km. The amplitude of the forced nutation in the liquid core models is also sensitive to the mean core radius. The sensitivity is high enough that measuring of the amplitudes of the three largest nutation components with an accuracy of a milliarcsecond will produce measures of the mean core radius with uncertainties of 32, 38, and 67 km, respectively. Elastic mantle, solid core models, however, are found to produce no significant difference in the motion of the pole compared to the rigid solid core model. Evidence for some sort of nonrigid polar motion is shown to exist from the Viking lander radar ranges of Mars. methods of obtaining higher quality observations of Mars' orientation in space, and the applicability of the methods derived for Mars to other planets in the solar system are discussed.