THE PROPOSED PROJECT WILL ENHANCE THE USABILITY AND CAPACITY OF A HIGHLY FLEXIBLE LANDFORM EVOLUTION MODELING FRAMEWORK KNOWN AS MARSSIM. THE MAIN AIMS OF THE PROPOSED EFFORT INCLUDE: PROVIDING A GRAPHICAL USER INTERFACE IMPROVING COMPUTATIONAL EFFICIENCY INCREASING MODEL AVAILABILITY THROUGH OPEN REPOSITORIES IMPLEMENTING FLEXIBLE AND COMMONLY USED DATA INPUT/OUTPUT FORMATS AND PROVIDING A VERSIONING AND REVISION FRAMEWORK. MARSSIM QUANTITATIVELY EVALUATES PROCESSES MODIFYING PLANETARY SURFACES INCLUDING ROCK WEATHERING MASS WASTING FLUVIAL EROSION SEDIMENT TRANSPORT AND DEPOSITION FLOW ROUTING OF SURFACE RUNOFF (INCLUDING EVAPORATION AND LAKES) IMPACT CRATERING GROUNDWATER FLOW AND SEEPAGE EROSION GLACIAL FLOW AND EROSION AEOLIAN DEPOSITION SUBLIMATION AND PRECIPITATION OF VOLATILES AND LAVA FLOW AND EMPLACEMENT. IT CAN SIMULATE MULTIPLE PROCESSES OPERATING EITHER SIMULTANEOUSLY AND/OR SEQUENTIALLY ACTING AT DIFFERENT RATES UPON THE LANDSCAPE. ORIGINALLY DEVELOPED FOR TERRESTRIAL STUDIES MARSSIM HAS SINCE BEEN APPLIED TO MARS THE MOON CALLISTO PLUTO HYPERION TITAN AND HELENE. MARSSIM IS PROGRAMMED IN STANDARD FORTRAN 95 AND HAS A COMMAND-LINE INTERFACE. THE MODEL IS PRESENTLY PUBLICALLY AVAILABLE THROUGH THE COMMUNITY SURFACE DYNAMICS MODELING SYSTEM (CSDMS). WE PROPOSE TO PROVIDE A GRAPHICAL USER INTERFACE AND DOCUMENTATION IN PYTHON A WIDELY-USED CROSS-PLATFORM ENVIRONMENT WITH GRAPHICAL INTERFACES. THIS PYTHON WRAPPER ON THE UNDERLYING FORTRAN CODE WILL MANAGE INPUT PARAMETERS (TOGETHER WITH HELP FILES AND PERMISSIBLE PARAMETER VALUES) AND INITIAL CONDITIONS AND OUTPUT FORMATS; MONITOR AND CONTROL PROGRAM EXECUTION (INCLUDING GRAPHICAL MONITORING OF SIMULATED LANDFORMS AND VALUES OF IMPORTANT OUTPUT VALUES); AND PROVIDE VISUALIZATION CAPACITY FOR PROGRAM RESULTS. THIS GRAPHICAL INTERFACE WILL MAKE THE MARSSIM PROGRAM MORE ACCESSIBLE FOR USERS WITH LIMITED PROGRAMMING EXPERIENCE AND WILL ALSO BE IDEAL AS A CLASSROOM-TEACHING TOOL. HOWEVER AT PRESENT THE MODEL LACKS A VERSIONING SYSTEM (E.G. SUBVERSION) THAT ALLOWS FOR SELECTIVE UPDATING AND SPECIALIZATION OF MODULES CONTROLLING INPUT/OUTPUT AND PROCESS FORMULATIONS. AS SUCH A VERSIONING SYSTEM WILL BE IMPLEMENTED. A NUMBER OF IMPROVEMENTS WILL BE MADE IN UPDATING A VARIETY OF NUMERICAL ALGORITHMS TO REFLECT THE ADVANCES IN COMPUTATIONAL METHODS OF THE LAST 3-5 YEARS INCLUDING IMPLEMENTATION OF SUPER-TIME STEPPING (BRINGING UP TO FIVE-TO-TEN FOLD IMPROVEMENTS IN COMPUTATIONAL EFFICIENCY OF NONLINEAR DIFFUSIVE PROCESSES) AND SOLVING SYSTEMS ON NON-UNIFORM GRIDS. THE MODEL INPUT AND OUTPUT DATA FORMATS AT PRESENT ARE IN A SIMPLE BUT NON-STANDARDIZED FORMAT FOR BOTH DATA MATRICES AND IMAGE DATA. A NUMBER OF USER-SELECTABLE INPUT-OUTPUT FORMATS WILL BE IMPLEMENTED INCLUDING NETCDF FOR MATRICES AND TIFF FOR IMAGES. OTHER FORMATS WE WILL UTILIZE ARE FITS HDF5 AND PDS4. A NUMBER OF ACCESSORY PROGRAMS ARE ALSO AVAILABLE IN THE PRESENT DISTRIBUTION INCLUDING OUTPUT FORMAT CONVERTERS AND PROGRAMS TO PROVIDE INITIAL CONDITIONS FOR SIMULATIONS INCLUDING CRATERED SURFACES LEVEL OR TILTED SURFACES AND PSEUDO-FRACTAL TERRAIN. WE WILL PROVIDE THE MODEL (WITH VERSIONING INTERFACE) EXAMPLE SIMULATIONS DOCUMENTATION AND A GRAPHICAL INTERFACE THROUGH SEVERAL REPOSITORIES INCLUDING NASA S GITHUB SITE CSDMS (WHICH ALSO USES GITHUB) AND THE PI S WEBSITE. PROGRAM RELEVANCE: ACCORDING TO ROSES APPENDIX C.7 THE OBJECTIVE OF THE PROGRAM IS TO PRODUCE TOOLS THAT WOULD ENABLE OR ENHANCE FUTURE SCIENTIFIC INVESTIGATIONS AND PRODUCTS OF SELECTED PROPOSALS WILL BE MADE AVAILABLE TO THE SCIENTIFIC COMMUNITY. THE AIMS OF THE WORK PROPOSED HERE DIRECTLY ADDRESS THESE OBJECTIVES AS WE PROPOSE TO UPDATE AND EXPAND THE UTILITY OF THE POWERFUL LANDFORM EVOLUTION TOOL MARSSIM AND MAKE IT ACCESSIBLE TO THE PLANETARY SCIENCE COMMUNITY AT LARGE.