MOTIVATION: KNOWLEDGE OF THE SPATIAL AND TEMPORAL DISTRIBUTION OF NEAR-SURFACE ICE IS IMPORTANT TO UNDERSTANDING THE HABITABILITY CLIMATE AND GEOLOGY OF MARS AND TO PREPARE FOR HUMAN EXPLORATION. RECENT NEUTRON AND GAMMA RAY SPECTROMETER IMAGING INDICATES PRESENT CONTINUOUS SHALLOW SUBSURFACE ICE AT MID-TO-HIGH LATITUDES THOUGH NOT AT TROPICAL LATITUDES BETWEEN +/-30 DEGREES NORTH. ICE-RELATED FEATURES FOUND AT HIGH LATITUDES ARE NOT SEEN AT LOW LATITUDES EXCEPT FOR LAYERED EJECTA CRATERS WHICH ARE THOUGHT TO FORM THEIR DISTINCT EJECTA BY TAPPING NEAR-SURFACE ICE. THUS ANALYSES OF LAYERED EJECTA CRATERS ARE KEY TO DETERMINING WHEN AND WHERE NEAR SURFACE ICE HAS BEEN PRESENT AT TROPICAL LATITUDES. RECENT WORK BY THE PI AND CO-I GRIMM DERIVING MODEL FORMATION AGES OF SEVERAL EQUATORIAL LAYERED EJECTA CRATERS INDICATES THESE CRATERS FORMED THROUGHOUT THE AMAZONIAN SUGGESTING BURIED ICE HAS BEEN AND STILL IS PRESENT IN THE TROPICS AT LEAST IN LOCALIZED AREAS. WHAT IS NOT UNDERSTOOD IS THE SPATIALLY HETEROGENEITY OF TROPICAL NEAR-SURFACE ICE AND IF ANY HETEROGENEITY HAS EVOLVED WITH TIME. THE LOCATION OF RADIAL EJECTA CRATERS THOUGHT TO FORM AS A CONSEQUENCE OF IMPACT INTO VOLATILE POOR TARGET MATERIALS WITHIN 10'S OF KMS OF LAYERED EJECTA CRATERS IMPLIES BURIED ICE COULD BE QUITE LOCALIZED. HOWEVER UNTIL FORMATION AGES OF BOTH LAYERED AND RADIAL EJECTA CRATERS ARE ASCERTAINED AND POSSIBLE CORRELATION OF AGE WITH SIZE AND LOCATION IS IDENTIFIED THE LOCAL EVOLUTION OF MARTIAN TROPICAL SUBSURFACE ICE ALONG WITH THE OVERALL EVOLUTION OF MARS' GROUNDWATER REMAINS AMBIGUOUS. .SCIENCE GOALS AND OBJECTIVES: THE SCIENCE OBJECTIVES WE PROPOSE ARE THE STEPS NEEDED TO ACHIEVE OUR OVERALL GOAL OF GAINING A BETTER UNDERSTANDING OF THE SPATIAL AND TEMPORAL EVOLUTION OF MARS'S EQUATORIAL NEAR-SURFACE ICE AND GLOBAL GROUNDWATER INVENTORY. WE SEEK TO DETERMINE: 1) THE MODEL FORMATION AGES OF LAYERED AND RADIAL. 2) IF RADIAL EJECTA ERODES AT A FASTER RATE THAN LAYERED EJECTA. 3) THE STATISTICAL SPATIAL-TEMPORAL CORRELATION OF CRATER AGES SIZES LOCATIONS AND EJECTA MORPHOLOGIES AND THE INFERRED SPATIAL HETEROGENEITY OF NEAR-SURFACE ICE THROUGH TIME. 4) NEW CONSTRAINTS FOR THE EVOLUTION OF MARS'S GROUNDWATER. .SUMMARY OF METHODOLOGY: WE HAVE SELECTED 60 RADIAL AND 60 LAYERED EJECTA CRATERS FROM THE ROBBINS AND HYNEK MARS GLOBAL CRATER DATABASE IN A REGION OF HIGHLANDS BETWEEN 0 TO 30 DEGREES SOUTH AND 340 TO 10 DEGREES EAST THAT ARE IMAGED BY THE MARS RECONNAISSANCE ORBITER (MRO) CONTEXT CAMERA (CTX). WE WILL USE CTX IMAGES TO IDENTIFY AND MEASURE SMALLER CRATERS (D<1 KM) SUPERPOSED ON THEIR EJECTA BLANKETS. THEN THE SUPERPOSED CRATER MEASUREMENTS WILL BE COMPILED INTO CRATER SIZE-FREQUENCY DISTRIBUTIONS TO ESTIMATE THE ABSOLUTE MODEL FORMATION AGES OF EACH CRATER. WE WILL COMPARE THE TEMPORAL PRODUCTION RATE OF THE RADIAL EJECTA CRATERS WITH ALL CRATERS TO DETERMINE THEIR PRESERVATION RATE. THEN WE WILL PERFORM TEMPORAL SPATIAL STATISTICAL ANALYSES TO DETERMINE IF AGES ARE CORRELATED WITH LOCATIONS SIZES AND EJECTA MORPHOLOGIES TO INFER THE SPATIAL HETEROGENEITY OF NEAR-SURFACE ICE WITH TIME. FINALLY RESULTS WILL BE SYNTHESIZED TO DETERMINE NEW CONSTRAINTS FOR THE EVOLUTION OF MARS'S GROUNDWATER. .