In this paper, computations of Mars' polar motion are presented for Mars models with three homogeneous layers as a function of the radius of the inner core and for different excitation possibilities ( atmosphere, ice caps, quakes). We estimated the amplitude of the two polar motion normal modes, i.e. the Chandler wobble and the Inner Core wobble, resulting from atmospheric excitation and for a reasonable interval of damping factor values. We show that the signature of the inner core in the polar motion is very small and is unlikely to be detected with the present observational precision. We further investigated the possibility of exciting the normal modes of Mars' polar motion through Marsquakes and show that the predicted quake moments are not large enough to excite polar motion to an observable level.