Searching for Evidence of Active Tectonics on Europa

Introduction: Voyager and Galileo showed that the surface of Europa has undergone significant reworking at some point during the moon’s history. The surface is covered in lineaments, which likely formed from the tides generated from Europa’s eccentric orbit around Jupiter [1]. There is also a relative paucity of visible impact craters, suggesting a surface age of about 80 million years [2]. Therefore, all of the visible surface features have formed within that time frame. This yields a maximum age of the surface, but the search for a minimum age for tectonic activity is more challenging. Ridgeless surface fractures [3] (also called troughs) are the youngest tectonic features on the surface, cross cutting all other fractures and occasionally regions of endogenic disruption (chaos). There have been several mechanisms to explain the formation of these fractures [1, 4-5], but the most likely of them seems to be formation by tectonic processes in the ice shell. The tectonic activity is likely caused by the tidal stress induced at the surface [1], but could also be a result of stresses induced by nonsynchronous rotation (NSR) of the ice shell, polar wander, or ice shell thickening. Europa is a good candidate to be currently undergoing active tectonics. Searching for the evidence of recent tectonic activity logically starts with the geologically young, ridgeless surface fractures. This project will develop comprehensive fracture maps of the re-cent surface fractures using the program Arc GIS. Fractures have been mapped onto spatially-referenced images with each fracture having a unique identifier and embedded information about the length and orientation, the fracture classification (described below), and the crosscutting relationship (older or younger) between young fractures that intersect. Preliminary mapping has identified at least six separate types of recent fractures that have distinct formation mechanisms: (1) tectonic fractures; (2) cycloidal fractures; (3) tailcracks; (4) endogenic process fractures; (5) flexure fractures; and (6) fold hinge fractures.