ICE DIAPIRS ON EUROPA - IMPLICATIONS FOR LIQUID WATER

Early examinations of Galileo images of Europa revealed features that look like low topographic. domes. These small (5-10 km in radius) dome s have been interpreted as surface manifestations of diapirs. As a way to probe the subsurface structure of Europa, we investigate the possi bility that thermally-driven ice diapirism created these surface featu res. We use a previously developed analytic model for rising diapirs t o estimate the initial radii of the diapirs, their initial depth, the temperature of the medium through which they rise and their formation timescales. We assume that the diapirs originate at the boundary layer between solid ice and whatever underlies it, whether it be liquid wat er or solid rock. Our results show that the diapirs originate at a dep th of no more than a few tens of kilometers. Since the H2O layer on Eu ropa is substantially thicker than this, our results support the view that liquid water recently existed beneath the ice on Europa at this l ocation, at a depth of no more than a few tens of kilometers. Further, the ice must have been warm (250-270 K) and was therefore likely to h ave been convecting.