CASSINI HAS FOUND EVIDENCE FOR A SUBSURFACE OCEAN ERUPTING PLUMES OF MATERIAL FROM ENCELADUS' SOUTH POLE. ANALYSES OF THE PLUMES SUGGEST A MODERATELY SALINE HIGH PH OCEAN ENVIRONMENT CONTAINING ORGANICS CARBON DIOXIDE METHANE AMMONIA ARGON AND MOLECULAR HYDROGEN. THIS COMPOSITION SUGGESTS A POTENTIALLY HABITABLE ENVIRONMENT THAT MAY BE FAVORABLE FOR ORIGIN-OF-LIFE SCENARIOS. THE ABILITY TO SAMPLE THE SUBSURFACE OCEAN VIA THE PLUMES MAKES ENCELADUS A STRONG CANDIDATE FOR PROPOSED MISSIONS E.G. THE 'ENCELADUS LIFE FINDER' (ELF) AND 'ENCELADUS LIFE SIGNATURES AND HABITABILITY' (ELSAH) MISSIONS. INFERRING THE DEEP OCEAN COMPOSITION FROM PLUME ANALYSES IS VITAL FOR PROPOSED MISSIONS AND REPRESENTS A GAP IN KNOWLEDGE BETWEEN PROPOSED INSTRUMENT SUITES AND SCIENCE RETURN. MEASUREMENTS OF ENCELADUS' PLUME MAY NOT DIRECTLY REFLECT THE OCEAN COMPOSITION BECAUSE EQUILIBRIUM AND NON-EQUILIBRIUM PROCESSES WILL FRACTIONATE OCEANIC WATERS DURING TRANSPORT TO THE SURFACE. EFFORTS TO MODEL EQUILIBRIUM AND NON-EQUILIBRIUM FRACTIONATION PROCESSES IN THE PLUME ARE HINDERED BY A LACK OF EXPERIMENTAL DATA AT LOW-TEMPERATURES AND HIGH SALT CONCENTRATIONS RELEVANT TO ENCELADUS. TO ADDRESS THESE ISSUES WE PROPOSE THREE TASKS TO: (1) MEASURE LOW-TEMPERATURE PROPERTIES OF GASES AND AQUEOUS SOLUTIONS RELEVANT TO ENCELADUS (2) INCORPORATE EXPERIMENTAL AND LITERATURE DATA INTO PREDICTIVE NUMERICAL MODELS AND (3) APPLY A BOX MODEL TO UNDERSTANDING THE SUBSURFACE OCEAN AND PLUME COMPOSITION. THE EXPERIMENTAL MEASUREMENTS IN TASK 1 TARGET PROCESSES THAT FORM ENCELADUS' PLUME AND KEY KNOWLEDGE GAPS THAT HINDER NUMERICAL MODELING EFFORTS. WE WILL MEASURE HEAT CAPACITIES OF AQUEOUS SOLUTIONS TO CONSTRAIN THE TEMPERATURE-DEPENDENCE OF AQUEOUS CHEMISTRY MODELS. TO UNDERSTAND THE POTENTIAL PRESERVATION OF ORGANICS WITHIN GLASSES IN PLUME PARTICLES WE WILL MEASURE GLASS TRANSITION TEMPERATURES AND CRYSTAL NUCLEATION RATES IN AQUEOUS SOLUTIONS. FINALLY WE WILL DIRECTLY INVESTIGATE PROCESSES THAT FORM ENCELADUS' PLUME IN GAS SOLUBILITY DISSOLUTION AND EXSOLUTION EXPERIMENTS. IN TASK 2 WE WILL INCORPORATE THE NEW DATA INTO NUMERICAL MODELS OF AQUEOUS CHEMISTRY. IN TASK 3 WE WILL APPLY NEW EXPERIMENTAL DATA AND AQUEOUS MODELS TO ENCELADUS USING A BOX MODEL THAT ACCOUNTS FOR PLUME FRACTIONATION AND MASS FLUXES FROM ITS SOURCE IN THE DEEP OCEAN TO THE ERUPTED PLUME IN SPACE. OUR GOAL IS TO CONSTRAIN WHICH DEEP OCEAN COMPOSITIONS ARE CONSISTENT WITH PLUME MEASUREMENTS BY CASSINI (AND FUTURE SPACECRAFT) AND THE POTENTIAL HABITABILITY OF THE OCEAN. THE OUTCOMES OF THIS RESEARCH WILL ADDRESS FUNDAMENTAL QUESTIONS ABOUT ENCELADUS' OCEAN INCLUDING: (1) WHAT DO PLUME MEASUREMENTS INDICATE ABOUT THE OCEAN COMPOSITION? (2) WHAT ARE THE HABITABILITY PARAMETERS OF THE OCEAN SUCH AS PH SALINITY WATER ACTIVITY AND FREEZING TEMPERATURE? ARE THERE CHEMICAL GRADIENTS IN THE OCEAN IMPORTANT FOR LIFE? (3) WHAT DO SOLID PHASES IN THE PLUME IMPLY ABOUT CONDITIONS IN THE PARENT FLUID? COULD AQUEOUS GLASSES PRESERVE ORGANICS IN ENCELADUS' PLUME? THIS RESEARCH IS ALSO RELEVANT FOR UNDERSTANDING AQUEOUS SOLUTIONS ON OTHER ICY WORLDS SUCH AS CERES EUROPA AND TITAN AS WELL AS LOW-TEMPERATURE AQUEOUS CHEMISTRIES ON EARTH AND MARS. OUR PROPOSED RESEARCH IS TIMELY BECAUSE OUR WORK WILL BETTER CONSTRAIN THE OCEAN CHEMISTRY AND POTENTIAL HABITABILITY USING EXISTING CASSINI DATA INFORM FUTURE PLANNING OF ENCELADUS MISSIONS AND ALLOW A RAPID AND MORE ACCURATE INTERPRETATION OF RESULTS RETURNED FROM FUTURE MISSIONS. EXPERIMENTAL WORK WILL DIRECTLY MEASURE GAS EXSOLUTION PROCESSES THAT FRACTIONATE PLUME MATERIALS AND ALLOW THE DEVELOPMENT OF AQUEOUS MODELS TO UNDERSTAND THE CHEMISTRY OF ENCELADUS' OCEAN. OVERALL OUR MODELING EFFORTS WILL RESULT IN BETTER CONSTRAINTS ON THE COMPOSITION OF ENCELADUS' PLUME AND HABITABILITY PARAMETERS IN ENCELADUS' OCEAN INCLUDING GAS COMPOSITION SALINITY PH WATER ACTIVITY AND TEMPERATURE.