GEODETIC EVIDENCE FOR POLAR WANDER ON MARS

Mars has long been considered a candidate planet for true polar wander, a reorientation of an entire planetary surface with respect to its spin axis. True polar wander on Mars may have resulted from changes in the inertia tensor as a result of redistribution of mass such as occurred during the rise of Tharsis. It has further been suggested that the occurrence, at low latitudes on Mars, of tensile structures,, grazing impacts, mantled terrain, paleomagnetic poles and anomalous moisture provide additional evidence for polar wander.

Mars currently has a polar radius some 22 km smaller than the equatorial radius. This is a considerable amount of flattening to be re-equilibrated completely had polar wander occurred at some time in the martian past. The Earth, for example, currently maintains an ellipticity about 0.5% greater than what would result from hydrostatic conditions in the interior. Some part of this excess ellipticity might represent a delay in the response of the equatorial bulge to the long-term slowing of the Earth's rotation. If Mars has undergone polar wander, then perhaps there is a remnant equatorial bulge in the martian geoid (the areoid) which can be used to locate the former spin axis. Recent geodetic data from the Mars Global Surveyor is used to evaluate this possibility