QUANTITATIVE MODELLING OF LINEAMENT HISTORY AND STRESSES ON EUROPA

It is uncertain whether Europa's level of geological activity has remained constant or dwindled in the geologically recent past, an issue critical to understanding the satellite's geology and potential habitability. We present initial results of efforts to combine GIS digital mapping, computer-assisted stratigraphic sorting, and potential-based stress modeling to determine the formational history of Europa's structures and the evolutionary history of the satellite.

Diurnal and nonsynchronous rotation stressing of Europa's surface is modeled by calculating the vector components of surface displacement, functions of the gravitational potential. The degree 2 Love numbers for an assumed ice shell thickness are used to determine the strain tensor, from which the stress tensor components are derived. This tensor is decomposed to obtain its eigenvectors and eigenvalues, which are the directions and magnitudes of the principal surface stresses.

To discern the temporal relationships among Europa's numerous lineaments, we have implemented a computer-assisted stratigraphic sorting technique. The system of intersecting lineaments as mapped using GIS is converted into a directed graph, in which each lineament is represented by a node, and each intersection is represented by an arc between nodes. We employ a topologic sort to order the nodes of a directed graph, requiring that no member can be reached from any node below it in the ordering. Topologic sorts are generally not unique, so we cannot be certain of lineament formation order, but the uncertainty in any particular lineament’s position in the sort can be quantified. Topologic sorts work only if the graph is acyclic, such that the lineaments formed in a clear sequence, and have not been reactivated. For Europa, if the graph is not acyclic we can enforce the acyclic condition to obtain an ordering, potentially inferring lineament reactivation. Equivalency classes are sets of lineaments with indistinguishable positions in the topologic sort, and should be approximately contemporaneous.

We will present results on quantitative comparisons between lineament orientations and plausible stress fields in the Conamara Chaos region, determining the most likely stress regime of formation for each set of temporally equivalent lineaments.