A CURRENT HYPOTHESIS FOR THE EARLY CLIMATE OF MARS POSTULATES THAT THE SOUTHERN HIGHLANDS WERE COVERED BY A COLD-LOCKED ICE SHEET (E.G. RECENT WORKS BY HEAD FASTOOK WADSWORTH AND OTHERS). THIS IS IN CONTRAST TO THE HYPOTHESIS THAT EARLY MARS WAS WARM AND WET AND MAINTAINED FAVORABLE CLIMATIC CONDITIONS FOR AN ACTIVE HYDROLOGICAL CYCLE AND EVEN A VAST NORTHERN OCEAN. CONTRADICTING RESULTS FROM CLIMATE MODELING AND OBSERVATIONS OF THE GEOLOGIC RECORD ON MARS MUST BE RECONCILED IN ORDER TO GAIN A MORE COMPLETE UNDERSTANDING OF THE PROCESSES THAT GOVERNED THE EVOLUTION OF THE SURFACE OF MARS AND ITS ASTROBIOLOGICAL POTENTIAL. THE OVERARCHING GOAL OF THIS PROPOSED RESEARCH IS TO HELP ASSESS THE CLIMATIC CONDITIONS ON MARS DURING THE LATE NOACHIAN BY COMPARING THE GEOMORPHIC PROPERTIES OF VALLEY NETWORKS TO THOSE PRODUCED FROM LANDSCAPE EVOLUTION MODELS. OUR PRIMARY OBJECTIVES FOR THIS EFFORT ARE TO: (1) CHARACTERIZE EXTENSIVE VALLEY NETWORKS ON MARS USING SEVERAL INDICES COMMON IN THE TERRESTRIAL GEOMORPHOLOGY COMMUNITY (2) RUN NUMERICAL LANDSCAPE EVOLUTION MODELS FORCED BY BOUNDARY CONDITIONS REPRESENTING BOTH THE WARM-WET AND COLD-ICY HYPOTHESES (PLUS INTERMEDIATE MODELS TO THESE END-MEMBERS) TO GENERATE THE SAME GEOMORPHIC INDICES AND (3) TEST THE COLD-ICY AND WARM-WET HYPOTHESES BY COMPARING OBSERVED VALLEY NETWORK MORPHOLOGY WITH MODELED RESULTS USING DEVELOPED METRICS FOR COMPARISON. TO ACCOMPLISH THESE OBJECTIVES WE PLAN TO: (1) MOSAIC HIGH-RESOLUTION DIGITAL ELEVATION MODELS (DEMS) FOR AREALLY EXTENSIVE MARTIAN VALLEY NETWORKS (2) ANALYZE DEMS WITH THE TOPOTOOLBOX PLUG IN FOR MATLAB USING CHANNEL-LONG PROFILES SLOPE-AREA PLOTS AND RIVER CROSS PROFILES (3) MODEL END-MEMBER AND INTERMEDIATE SCENARIOS FOR AN ICY-COLD AND WARM-WET ENVIRONMENT IN VETTED LANDSCAPE EVOLUTION MODELS (I.E. LANDLAB AND MARSIM) WITH EXISTING AND ALSO MODIFIED COMPONENTS FOR CHANNEL INCISION DISTURBANCEDRIVEN DIFFUSION PRECIPITATION AND ICE SHEET MELTING AND (4) COMPARE THE EMPIRICAL RESULTS FROM THE MARTIAN SURFACE WITH PREDICTED MORPHOLOGIES PRODUCED FROM THE MODELING SCENARIOS. WE ANTICIPATE THAT THE RESULTS OF THIS RESEARCH WILL PROVIDE NEW INSIGHTS INTO THE CONDITIONS OF THE MARTIAN CLIMATE DURING THE LATE NOACHIAN. SPECIFICALLY THIS RESEARCH WILL ADD NOVEL (FOR MARS) QUANTITATIVE GEOMORPHIC TESTS TO ASSESS WHETHER THE ANCIENT CLIMATE WAS WARM AND WET COLD AND ICY OR SOMEWHERE IN BETWEEN. IF COLD-ICY HIGHLANDS CLIMATE MODELING PREDICTIONS ARE CORRECT THE OBSERVED MORPHOLOGICAL CHARACTERISTICS OF VALLEY NETWORKS SHOULD BE VALIDATED BY MODELING EFFORTS IN THOSE LANDSCAPE EVOLUTION MODELING SCENARIOS. IF THE GEOMORPHIC FEATURES AND INDICES ARE ONLY CONSISTENT WITH WARM-WET LANDSCAPE MODELING THEN NEW CONSTRAINTS MUST BE ADAPTED FOR FUTURE CLIMATE MODELS. THIS PROPOSED RESEARCH DIRECTLY CONTRIBUTES TO NASA'S MEPAG'S GOAL II OBJECTIVE C "UNDERSTAND THE PROCESSES AND HISTORY OF CLIMATE ON MARS' BY "CHARACTERIZING MARS' ANCIENT CLIMATE AND UNDERLYING PROCESSES" AND ALSO GOAL III OBJECTIVE A "UNDERSTAND THE ORIGIN AND EVOLUTION OF MARS AS A GEOLOGICAL SYSTEM" BY "DOCUMENTING THE GEOLOGIC RECORD PRESERVED IN THE CRUST AND INTERPRETING THE PROCESSES THAT HAVE CREATED THAT RECORD." THIS EFFORT WILL ALSO ADDRESS MDAP'S TOP LEVEL GOAL BY ENHANCING THE SCIENTIFIC RETURN FROM MISSION DATA AND WE EXPECT TO INCORPORATE MULTIPLE DATASETS FROM MARS EXPRESS MARS GLOBAL SURVEYOR AND MARS RECONNAISSANCE ORBITER. WE WILL COMPLETE DATA ANALYSIS THEORETICAL WORK AND MODELING BASED ON THE EXISTING DATASETS. THE VALLEY NETWORKS ARE PARAMOUNT TO UNDERSTANDING OF THE HISTORY OF WATER ON MARS AND ITS PAST CLIMATE WHICH IS ESSENTIAL IN ASSESSING MARS' ASTROBIOLOGICAL POTENTIAL.