IMPACT CRATERING IS THE MOST COMMON GEOLOGIC PROCESS IN THE SOLAR SYSTEM. BY VIRTUE OF ITS RELATIVELY SIMILAR SURFACE PROPERTIES TO THE MOON (AIRLESS HEAVILY CRATERED TERRESTRIAL BODY) ITS SIMILAR GRAVITY TO MARS AND ITS ENDMEMBER STATUS IN TERMS OF IMPACT VELOCITY MERCURY IS A KEY LINK TO UNDERSTANDING HOW VARIATIONS IN TARGET AND IMPACTOR PROPERTIES ALTER THE IMPACT PROCESS. WE PROPOSE THREE TASKS TO STUDY THE MERCURIAN IMPACT CRATER POPULATION USING MESSENGER DATA. IN OUR FIRST TASK WE WILL UPDATE AND IMPROVE THE GLOBAL CRATER LOCATION AND MORPHOLOGY DATABASE THAT WE PREVIOUSLY CREATED USING ONLY FLYBY DATA FROM MESSENGER AND MARINER 10. THE MESSENGER ORBITAL IMAGES PROVIDE IMPROVED RESOLUTION AND FAVORABLE SUN ANGLES FOR A LARGE PORTION OF THE PLANET AND THIS ENABLES SUBSTANTIAL IMPROVEMENTS FROM THE FIRST VERSION OF THE DATABASE. WE DESIRE TO REFINE THE MORPHOLOGICAL CLASSIFICATION SCHEME TO ENHANCE THE UTILITY OF THE DATABASE FOR END USERS. WE ALSO DESIRE TO EXTEND THE DATABASE TO SMALLER DIAMETERS IN ORDER TO CAPTURE THE FULL RANGE OF CRATER MORPHOLOGIES IN THE SIMPLE-COMPLEX CRATER TRANSITION A KEY TRANSITION FOR STUDIES OF IMPACT CRATERING MECHANICS. IN THE SECOND TASK WE WILL SELECT A SUBSET OF THE BEST-PRESERVED CRATERS AND CONDUCT A NUMBER OF MORPHOMETRIC MEASUREMENTS. WE WILL ANALYZE THE MORPHOLOGICAL AND MORPHOMETRIC DATA OF TASKS 1 AND 2 TO IDENTIFY REGIONAL TRENDS AND DRAW INFERENCES REGARDING THE IMPACT PROCESS. THE DATA FROM TASKS 1 AND 2 WILL BE UTILIZED TO SELECT STUDY CRATERS FOR TASK 3. IN TASK 3 WE WILL STUDY CRATERS OF SIMILAR SIZE BUT DIFFERENT MORPHOLOGIES IN THE DIAMETER RANGE FOR THE SIMPLE-COMPLEX TRANSITION AND THE CENTRAL-PEAK TO PEAK-RING TRANSITION. CRATERS OF SIMILAR SIZE LIKELY FORMED FROM SIMILAR KINETIC ENERGIES. USING DETAILED GEOLOGIC ANALYSES OF THESE TRANSITION-ZONE CRATERS WE WILL ISOLATE SOME OF THE EFFECTS OF VARYING IMPACTOR AND TARGET PROPERTIES ON THE CRATERING PROCESS. THE PROPOSED WORK WILL NOT ONLY ADVANCE KNOWLEDGE OF CRATERING MECHANICS BUT WE WILL BUILD KNOWLEDGE THAT WILL ENHANCE OUR ABILITY TO USE CRATER MORPHOLOGY TO PROVIDE UNIQUE INFORMATION ABOUT A PLANET'S CRUSTAL PROPERTIES PARTICULARLY WITH RESPECT TO REGIONAL VARIATIONS IN MERCURY'S CRUST. ALSO THE DATA SETS DEVELOPED IN TASKS 1 AND 2 WILL BE EXTENSIVELY USED BY OTHER RESEARCHERS. THE TASKS IN THIS PROPOSAL UTILIZE IMAGES AND ALTIMETRY DATA FROM THE MESSENGER MISSION TO UNDERSTAND GEOLOGIC PROCESSES ON THE PLANET MERCURY CONSISTENT WITH THE STATED REQUIREMENTS OF PMDAP. THE PROPOSED WORK IS CONSISTENT WITH NASA'S SCIENTIFIC GOAL OF UNDERSTANDING THE FORMATION AND EVOLUTION OF SOLAR SYSTEM PLANETS.