True polar wander of Enceladus from topographic data

Abstract

Many objects in the solar system are suspected to have experienced reorientation of their spin axes. As their rotation rates are slow and their shapes are nearly spherical, the formation of mass anomalies, by either endogenic or exogenic processes, can change objects’ moments of inertia. Therefore, the objects reorient to align their largest moment of inertia with their spin axis. Such a phenomenon is called True Polar Wander (TPW). Here we report the discovery of a global series of topographic lows on Saturn's satellite Enceladus that we interpret to show that this synchronously locked moon has undergone TPW by ∼55° about the tidal axis. We use improved topographic data from the spherical harmonic expansion of Cassini limb and stereogrammetric measurements to characterize regional topography over the surface of Enceladus. We identify a group of nearly antipodal basins orthogonal to a basin chain tracing a non-equatorial circumglobal belt across Enceladus' surface. We argue that the belt and the antipodal regions are fossil remnants of earlier equator and poles, respectively. We argue that these lows arise from isostasic compensation and that their pattern reflects spatial variations in internal dynamics of the ice shell. Our hypothesis is consistent with a variety of geological features visible in Cassini images.