| True polar wander (TPW) is the movement of the rotation axis with respect to surface topography or internal signatures of a deformable rotating body. Both TPW and differential rotation of surface layers with respect to deeper layers inside the rotating body have been proposed to explain tectonic stress patterns on Europa, position of diapirs on Enceladus and even ?real-time observed? longitudinal drifts of topographic features on Titan. Although such observations, indicating the importance of TPW and differential rotation for icy moons, have abounded in recent years, they have hitherto not been modeled by means of numerical rotationally and gravitationally fully self-consistent dynamical viscoelastic relaxation models. Usually numerical models remain limited to simplified assumptions concerning rotation dynamics in the elastic or fluid limit without explicitly modeling transient dynamical evolution. In this project, TPW and differential rotation are to be modeled for icy moons with shallow low-viscosity zones. This project will be innovative in two respects. TPW will be modeled by taking load-induced and tidal- and centrifugally-induced viscoelastic relaxation gravitationally self-consistently into account, thereby not being constrained to elastic or fluid limits. The second innovative aspect relates to modeling of shallow zones with extremely low viscosities (both inviscid and slush-like) and their influence on TPW and longitudinal shifts, again with gravitationally and rotationally self-consistent relaxation models. It is expected that the outcome of these models will considerably limit the range of scenarios and possibilities proposed for purportedly observed rotational variations on icy moons, and even might discard some of the proposed mechanisms. |
