Chandler wobble and Free Core Nutation for Mars

The NetLander Ionospheric and Geodesic Experiment (NEIGE) of the 2007 NetLander/Mars Sample Return mission will allow the determination of Mars’ orientation parameters. Two normal rotational modes of Mars are studied here which can play an important role in these quantities: the Free Core Nutation (FCN) and the Chandler wobble (CW). The influence of various rheological and structural assumptions about the planet on the periods of these modes is investigated. Special attention is paid to the effects of inelasticity and the possible presence of a solid inner core. It is found that inelasticity has an almost negligible effect on the FCN period but can change the CW period by several days. The presence of an inner core, on the other hand, almost does not influence the CW period but can cause important changes to the FCN period. For the FCN, also nonhydrostatic effects can have a large impact on the period. These additional factors determining the FCN period, besides core size and density, certainly complicate the procedure for deriving information on the core of Mars such as the core radius, but more importantly offer the possibility to study and constrain a wide variety of inner core outer core and mantle properties.