THE GALILEAN SATELLITES WITH ICY SURFACES (EUROPA GANYMEDE CALLISTO) ARE HOST AMONG OTHER THINGS TO A VARIETY OF LARGE IMPACT FEATURES THAT ARE IF NOT UNIQUE TO THESE BODIES RARELY ENCOUNTERED ON PLANETARY AND SATELLITE SURFACES IN THE SOLAR SYSTEM. THESE FEATURES INCLUDE IMPACT BASINS WITH CENTRAL PITS DOMED FLOORS AND SO-CALLED "PENEPALIMPSESTS" AND "PALIMPSESTS" IN THE TERMINOLOGY OF SCHENK (2005). IT IS LIKELY THAT THE PARTICULAR COMBINATION OF GEOPHYSICAL FACTORS AND IMPACTOR CHARACTERISTICS THAT IS SHARED BY THESE SATELLITES IS RESPONSIBLE FOR THESE FEATURES. OUR PROPOSAL WILL ADVANCE AND TEST HYPOTHESES FOR THE CAUSES OF THE CHARACTERISTICS OF THESE BASINS. WE HYPOTHESIZE THAT THE PARTICULAR PROPERTIES OF THE FORMATION OF THESE BASINS ARE GOVERNED MORE SPECIFICALLY BY THE INTERPLAY OF SEVERAL FACTORS: 1) THE PRESENCE OR ABSENCE OF A LIQUID WATER MELT POOL (EITHER PRE-EXISTING AT DEPTH BELOW THE SURFACE OR GENERATED DURING THE IMPACT) VS WARM ICE (AGAIN EITHER PRE-EXISTING OR IMPACT-GENERATED) 2) THE LITHOSPHERIC TEMPERATURE GRADIENT 3) SURFACE GRAVITY (AS COMPARED TO SMALLER GRAVITY ON MID-SIZED SATELLITES WHERE THE FEATURES OF INTEREST ARE NOT FOUND AND FINALLY 4) THE ROLE OF THE CHARACTERISTICS OF THE IMPACTOR: SPECIFICALLY THE IMPACTOR'S SIZE VELOCITY COMPOSITION AND THE ANGLE OF THE IMPACT. WE HAVE FORMULATED SPECIFIC AND TESTABLE HYPOTHESES ABOUT THE ROLE OF EACH OF THESE FACTORS IN THE FORMATION AND EVOLUTION OF THE IMPACT BASINS. THE PRIMARY WORK THAT WE PROPOSE TO CARRY OUT WILL BE DETAILED MODELLING OF THE FORMATION AND EVOLUTION OF THESE IMPACT FEATURES. OUR MAIN TOOLS FOR THE PROPOSED WORK WILL BE 1) THE CTH CODE FROM SANDIA NATIONAL LABORATORY AND 2) THE MARC CODE FROM MSC SOFTWARE. CTH IS A POWERFUL AND FLEXIBLE HYDRODYNAMICS CODES THAT ARE IN WIDESPREAD USE IN THE PLANETARY SCIENCE COMMUNITY. WE WILL USE CTH FOR SIMULATING THE EARLY-TIME GENERATION OF IMPACT CRATERS THAT SET THE STAGE FOR LATE-TIME EVOLUTION THAT WILL DETERMINE THE FINAL CHARACTERISTICS OF THE IMPACT FEATURES. THE MARC CODE WILL BE USED TO MODEL LONG-TERM PROCESSES THAT DETERMINE IMPACT BASIC CHARACTERISTICS. MARC SIMULATES MULTIPLE PHYSICAL PROCESS INCLUDING THERMAL DIFFUSION AND RHEOLOGICAL PHYSICS FOR ELASTIC PLASTIC AND VISCOUS FLOW. THIS PACKAGE IS WELL SUITED FOR STUDY OF CREEPING FLOW OF GEOLOGICAL MATERIALS AND COI DOMBARD AND COLLABORATORS HAVE USED IT EXTENSIVELY FOR THE STUDY OF TOPOGRAPHIC MODIFICATION ON VARIOUS BODIES INCLUDING ICY SATELLITES. THE FINAL OUTPUT OF THE MARC CALCULATIONS WILL BE COMPARED QUANTITATIVELY AND STATISTICALLY AGAINST THE IMPACT FEATURE FACIES AND TOPOGRAPHY TO DETERMINE WHICH OF THE SPECIFIC HYPOTHESES FOR THE FORMATION OF LARGE IMPACT FEATURES ON THE GANYMEDE AND CALLISTO. ULTIMATELY THE WORK IN THIS PROPOSAL WILL RESOLVE A LONG-STANDING PROBLEM THAT HAS PUZZLED THE OUTER-PLANET SCIENCE COMMUNITY FOR SEVERAL DECADES. ADDITIONAL WORK WILL BE CARRIED OUT BY THE TEAM TO IMPROVE MAPPING AND CREATION OF IMPROVED DIGITAL ELEVATION MODELS FOR RELEVANT IMPACT FEATURES.