Brine mobilization during lithospheric heating on Europa: Implications forformation of chaos terrain, lenticula texture, and color variations

The background lineated plains on Europa are locally highly modified and de stroyed in regions known as chaos and lenticulae. Produced there are (1) is olated fragments and polygons of background material which rotate and trans late, (2) matrix, which fills in the areas between the fragments and polygo ns, and (3) surface discolorations. Using observations and constraints from high-resolution Galileo images, we find that a model for the formation of these terrains which involves mobilization and migration of brines, and a p ossible percolation phase transition as the Europan lithosphere is warmed, can readily explain the vast majority of their characteristics. In addition , the presence of melt fractions of a few percent in the adjacent ice frame work may enhance the creep rate and the accompanying deformation rates. The characteristics and distribution of lenticulae suggest that among the stro ng candidates for heat sources for brine migration and ice mobilization pro cesses is diapirism linked to solid-state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer.