GLOBAL GEOLOGIC MAPPING OF ENCELADUS

The unusual geology of the Saturnian moon Enceladus was first recognized in images of the satellite returned by the Voyager spacecraft during their encounters with Saturn. Those images revealed a surface with evidence of tectonic activity and episodic partial resurfacing; suggesting a geologic history that was remarkably complex for a moon with a mean radius of ~250 km. The Cassini mission to Saturn has provided a wealth of additional information regarding the diverse geology of Enceladus. Most notable has been the detection of active plumes containing water vapor, dust, and other materials erupting from fractures near its south pole. The fractures, along with the terrain that surround them, are bound by a circumpolar chain of south-facing scarps and confined mountain chains that together define a geologic province referred to as the South Polar Terrain (SPT). Analyses of this region have revolutionized our understanding of the evolution of icy satellite surfaces. However, Enceladus’ south polar terrain tells only the most recent part of the story of this unique icy body. The rest of the story is buried in and, to some extent, obscured by: 1) the complex geological relationships between the SPT and other recognized geologic provinces on Enceladus, 2) the distribution and density of observed craters on the surface, and 3) the distribution, orientations, and cross-cutting relationships of tectonic features across the surface of Enceladus. Distinct geologic provinces on the leading and trailing hemispheres of Enceladus that share characteristics with the SPT have been recognized. Analyses of these provinces, and their relationship to each other, have provided insight into the thermal evolution of the satellite, the potential for reorientation of its spin-pole axis, and the potential for variability in the rheological and mechanical properties of its icy shell. The conclusions drawn from these analyses each provide a piece to the puzzle that represents the geologic history of Enceladus’ surface. Understanding that history requires integrating these insights (and others) into a self-consistent picture of the surface evolution of this unusual moon and here we report on progress toward that goal.