THE SOUTH POLAR TERRAIN (SPT) ON ENCELADUS (THOMAS ET AL. 2007) IS CHARACTERIZED BY PLUME ACTIVITY IN WHICH JETS OF VAPOR AND ICE EMANATE FROM FOUR LONG TIDALLY-CONTROLLED FRACTURES CALLED THE TIGER STRIPES (PORCO ET AL. 2006). A THERMAL ANOMALY OF ~10 GW ASSOCIATED WITH THE SPT HAS BEEN MEASURED WITH THE COMPOSITE INFRARED SPECTROGRAPH ON CASSINI (SPENCER ET AL. 2013) AND CORRELATES WITH THE LOCATION OF THE TIGER STRIPES. TIDAL DISSIPATION IS THE PROBABLE ENERGY SOURCE BUT THE EXPECTED PATTERN OF TIDAL HEATING IS SYMMETRIC ABOUT THE EQUATOR (BEUTHE 2013). HOWEVER THE HEAT FLOW AND ACTIVITY ARE OBSERVED ONLY IN THE SOUTH; NO CORRESPONDING THERMAL ANOMALY IS OBSERVED IN THE NORTH. ONE WAY TO BREAK THE SYMMETRY IN TIDAL HEATING WOULD BE LATERAL VARIATIONS IN THE THICKNESS AND STRENGTH OF THE ICE SHELL (BEHOUNKOVA ET AL. 2011) BUT A PHYSICAL MECHANISM IS NECESSARY TO ESTABLISH THIS MECHANICAL ASYMMETRY. .WORK PERFORMED UNDER A PRECURSOR GRANT STUDIED THE EFFECTS OF A LARGE IMPACT ON THE THERMAL EVOLUTION OF THE SPT. THE RESULTS OF THIS HYDROCODE MODELING INDICATE THAT A ~10 KM DIAMETER IMPACTOR WILL PENETRATE A THIN (~20 KM) ICE SHELL OR LEAVE A HIGHLY FRACTURED CRATER FLOOR IN A THICK (~40 KM) ICE SHELL; IN EITHER CASE EXPOSING THE SUBSURFACE OCEAN TO SPACE. THE IMPACT BREAKS THE SYMMETRY FORMS LONG-WAVELENGTH TOPOGRAPHY SIMILAR TO THAT OF THE PRESENT-DAY SPT AND ALLOWS FOR ENHANCED PLUME ACTIVITY AND HEAT FLOW IN THE IMPACTED REGION FOR SEVERAL MY. .HERE WE PROPOSE TO TEST THE SCENARIO DESCRIBED ABOVE AND DETERMINE IF THERE IS PRESERVED GEOLOGIC EVIDENCE OF THE EVENT. THE SIZE OF A PUTATIVE SOUTH POLAR IMPACT CRATER IS UNKNOWN BUT CANNOT BE LARGER THAN THE SIZE CURRENT SPT ROUGHLY 150 KM DIAMETER. IT IS POSSIBLE THAT NOT ALL THE SPT IS PART OF THIS CRATER AND THAT REGIONAL HEATING LATER MODIFIED THE ICE BEYOND THE EXTENT OF THE ORIGINAL CRATER. THE LACK OF CRATERS SUGGESTS THE SPT IS YOUNG AND ANY ORIGINAL IMPACT STRUCTURE WOULD HAVE BEEN HEAVILY MODIFIED BY GEOLOGIC ACTIVITY. THE BEST POSSIBLE EVIDENCE WOULD BE FOUND FAR FROM THE IMPACT SITE. WE FOCUS ON TWO POTENTIAL SIGNATURES FOR SUCH AN IMPACT: 1) SECONDARY CRATERS RADIATING AWAY FROM THE SPT; AND 2) DEGRADATION IN CRATER MORPHOLOGY WITH LATITUDE. .THIS DATA ANALYSIS EFFORT PURSUES TWO BROAD SCIENTIFIC OBJECTIVES. .OBJECTIVE 1: TO SEARCH FOR EVIDENCE THAT A LARGE IMPACT OCCURRED IN WHAT IS NOW THE SPT OF ENCELADUS. OBJECTIVE 2: TO ASSESS THE PROBABILITY OF AN SPT-FORMING IMPACT EVENT AS A FUNCTION OF TIME AND EVALUATE THE LIKELIHOOD THAT THE OBSERVED ACTIVITY IS IMPACT DRIVEN. .WE PROPOSE THREE TASKS: .TASK 1: MODEL THE EJECTA DISTRIBUTION FORMATION OF SECONDARY CRATERS AND LONG-TERM TECTONIC DEFORMATION THAT RESULTS FROM AN IMPACT CAPABLE OF FORMING A CRATER THE SIZE OF THE SPT. .TASK 2: EXAMINE CASSINI IMAGING SCIENCE SUBSYSTEM DATA TO LOOK FOR SECONDARY CRATERS RADIATING FROM THE SPT. LOOK FOR A PATTERN OF DEGRADATION OF OLDER CRATERS THAT DECREASES WITH LATITUDE WHICH WOULD INDICATE OVERPRINTING OF THE ORIGINAL CRATER TOPOGRAPHY WITH EJECTA. LOOK FOR EVIDENCE OF A CRATER RIM OR OTHER TECTONIC DEFORMATION THAT WOULD SUGGEST A REMNANT CRATER STRUCTURE. .TASK 3: DETERMINE THE EXPECTED INTERVALS OF SPT-FORMING EVENTS USING ESTABLISHED CRATER SIZE-FREQUENCY DISTRIBUTIONS FOR THE OUTER SOLAR SYSTEM. EVALUATE THE CONSISTENCY OF THIS TIMESCALE WITH THAT OF THE THERMAL EFFECTS PREDICTED FROM IMPACT AND GEOPHYSICAL MODELS. .THE PROPOSED WORK IS PRIMARILY ANALYSIS OF CASSINI IMAGING DATA IN ORDER TO ANALYZE THE GEOLOGIC HISTORY OF ENCELADUS. THE TASKS ARE THUS DIRECTLY RELEVANT TO CDAP'S OBJECTIVE OF BROADENING THE SCIENTIFIC PARTICIPATION IN THE ANALYSIS AND INTERPRETATION OF THE DATA RETURNED BY THE MISSION. OUR ANALYSIS ALSO ADDRESSES TWO OF THE CASSINI MISSION GOALS FOR ENCELADUS: DETERMINE THE CHARACTERISTICS AND GEOLOGICAL HISTORY OF ENCELADUS AND DEFINE THE DIFFERENT PHYSICAL PROCESSES THAT CREATED THE SURFACE OF ENCELADUS. .