1. Lineament Orientations through Time Near Europa’s Leading Point: Implications for Stress Mechanisms and Rotation of the Icy Shell Michelle M. Stempel and Robert T. Pappalardo LASP, CU-Boulder

2. Overview Demonstrate the stress pattern on the surface of Europa and how it changes with dependence. Explain fracture-formation models. Match lineament orientations in an equatorial region of Europa to a fracture-formation model. Place an upper limit on the number of degrees of rotation of the icy shell.

3. Nonsynchronous Stressing Mechanism

4. Stress pattern sweeps across the surface of Europa

5. Failure Models to Consider Faults can form: perpendicular to tensile stresses (left) in conjugate pairs when only compressive stresses are present (right), as in ECZ at 30-45˚ from greatest compressive stress for an icy lithosphere

6. Global Image Mosaic of Europa Study Area

7. Galileo E15REGMAP02 observation at~235 m/pixel.

8. Lineament orientations within each inferred stratigraphic level. youngest oldest

9. What can we conclude? E-W lineaments are predicted by formation due to an Equatorial Tensile Zone. The orientations shown are consistent with formation of lineaments within an Equatorial Compressive Zone. Upper limit of 90˚ of rotation of the icy shell. All 52 mapped lineaments are plotted. Note the distinct lack of North-South (N-S) and East-West (E-W) lineaments.

10. Future Work Determine stratigraphy lineament by lineament, using Geographic Information System (GIS) software. (current research) Evaluate precise stratigraphy to find examples of lineament orientation interweaving. Model the surface stresses of Europa and the regions where shear failure is expected. (to be completed this summer) Match lineament orientations to the stress model predictions, to rigorously determine an upper limit on the number of degrees of rotation of the icy shell of Europa. Predictions can be tested with future Europa Orbiter.