Topographic evidence of True Polar Wander on Enceladus

Abstract:

The peculiar presence of the active hotspot at Enceladus' south pole raises the question of whether it formed in situor if the satellite reoriented over time and moved the hotspot there from a different location. Here we extend a spherical harmonic reconstruction of Enceladus’ shape to order 16 by combining Cassini limb profile data with the positions of a large, globally distributed collection of surface control points. We have discovered an aligned arrangement of deep topographic lows that define a circumglobal valley lying along a non-equatorial great circle across Enceladus' surface. In addition, we have found two antipodal basins located about 90 degrees from the great circle. We argue that these structures are evidence of True Polar Wander of an angle 75 to 90 degrees, where the great circle and the antipodal regions are remnants of old equator and poles, respectively.

Modeling of heat transport in Enceladus’ sub-surface ocean suggests that heat flux along the ice-ocean interface is strongest and weakest at high and low latitudes, respectively. The resulting basal melt/freeze distribution may produce latitudinal variations in ice shell thickness and density that can create the topographic depressions apparent at the surface through isostatic adjustment. Our hypothesis also agrees well with the surface geological features visible in Cassini images.