PROPOSAL SUMMARY: ENERGETIC PROTONS ARE HEAVILY LOST IN SATURN S INNER MAGNETOSPHERE DUE TO CHARGE-EXCHANGE COLLISIONS WITH THE NEUTRAL GAS FROM ENCELADUS. THEIR FLUXES (OR FLUX DEPLETIONS) ARE A GOOD WAY TO MAP THE GAS DENSITIES AND BOUNDARIES. IT IS THEORETICALLY PREDICTED THAT ENERGETIC WATER GROUP IONS IN APPROXIMATELY THE SAME ENERGY RANGE WOULD ALSO INTERACT STRONGLY WITH THE NEUTRALS AND BE LOST. BUT DATA FROM THE MAGNETOSPHERE IMAGING INSTRUMENT (MIMI) AT EVERY PHASE OF THE MISSION DOES NOT SHOW THIS TO BE THE CASE. RATHER IN REGIONS WHERE THE PROTON ENERGY SPECTRUM CAN BE WELL MODELED ASSUMING THAT CHARGE EXCHANGE IS THE DOMINANT LOSS PROCESS THE OXYGEN ENERGY SPECTRUM APPEARS TO BE INCONSISTENT WITH THAT SAME LOSS MECHANISM. THIS IS A PERSISTENT MYSTERY IN THE MIMI DATA AND IN THIS PROPOSAL WE WOULD LIKE TO CARRY OUT A SYSTEMATIC DATA ANALYSIS APPROACH TO RESOLVE IT. THE SOLUTION HAS CONSEQUENCES FOR THE DISTRIBUTION OF THE NEUTRAL GAS AT SATURN AND THE ULTIMATE SOURCE COMPOSITION AND CHARGE STATE OF ENERGETIC HEAVY IONS. SCIENCE QUESTIONS: (1) HOW CAN LOW-CHARGE STATE ENERGETIC WATER GROUP IONS SURVIVE WITHIN THE CIRCUMPLANETARY NEUTRAL GAS DISTRIBUTION AT SATURN? (2) WHAT PROCESSES ARE GOVERNING THE TRANSPORT AND INTERACTIONS BETWEEN ENERGETIC HEAVY IONS AND SATURN S NEUTRAL GAS TORUS? (3) WHAT ARE THE DIFFERENCES BETWEEN ENERGETIC PROTONS AND WATER GROUP IONS REVEALING ABOUT THE GAS DISTRIBUTION OR THE SOURCE COMPOSITION CHARGE STATE AND LOSS OF THE IONS? METHODOLOGY: (1) ANALYZE MIMI DATA AND FORM MISSION-AVERAGES OF RELEVANT ION ENERGIES AND CHARGE STATES. (2) ANALYZE PITCH ANGLE DISTRIBUTIONS AS A FUNCTION OF LOCATION IN THE MAGNETOSPHERE. THESE ARE AFFECTED BY ABSORPTIONS BY NEUTRALS AND INDICATE WHICH SPECIES ARE MOST AFFECTED BY THE GAS. (3) COMPARE THE MEASUREMENTS WITH SIMPLE MODELS THAT ACCOUNT FOR LOSSES IN GAS AND OTHER PROCESSES TO RESOLVE THE PHYSICS BEHIND THE MYSTERY. RELEVANCE TO CDAP: THIS PROPOSAL SEEKS TO ENHANCE THE SCIENTIFIC RETURN OF THE CASSINI MISSION BY ADDRESSING OPEN QUESTIONS RELATED TO SATURN S MAGNETOSPHERE USING CASSINI DATA. THE AO STATES THE OBJECTIVE OF CDAP IS TO INCREASE THE PARTICIPATION IN THE ANALYSIS OF CASSINI DATA. THE PI OF THIS GRANT IS NOT FUNDED BY ANY CASSINI TEAMS.