Tidal reorientation and the fracturing of Jupiter's moon Europa

The most striking characteristic of Europa is the network of long linear albedo markings over the surface, suggestive of global-scale tectonic processes. Various explanations for the fractures have been proposed: Freezing and expansion of an early liquid water ocean¹, planetary expansion due to dehydration of hydrated silicates², localization by weak points in the crust generated by impacts³, and a combination of stresses due to planetary volume change and tidal distortions from orbital recession and orbital eccentricity^4,5. Calculations by Yoder⁶ and Greenberg and Weidenschilling⁷ have shown that Europa may rotate slightly more rapidly than the synchronous rate, with a rotation period (reorientation through 360°) ranging from 20 to >10³ yr if a liquid mantle is present, or up to 10¹⁰ yr if the satellite is essentially solid⁷. Helfen-stein and Parmentier⁸ modelled the stresses due to nonsynchronous rotation, and concluded that this could explain the long fractures in part of the anti-jovian hemisphere. In this note, I present a global map of lineaments with long arc lengths (>20° or 550 km), and compare the lineament orientations to the tensile stress trajectories due to tidal distortions (changes in the lengths of three principal semiaxes) and to nonsynchronous rotation (longitudinal reorientation of two of the principal semiaxes). An excellent orthogonal fit to the lineaments is achieved by the stresses due to nonsynchronous rotation with the axis radial to Jupiter located 25° east of its present position. This fit suggests that nonsynchronous rotation occurred at some time in Europa's history.