OUR OBJECTIVE IS TO IMPROVE INTERPRETATION OF IN SITU AND REMOTE-SENSING DATA OF MERCURY. WE WILL USE UPDATED EXOSPHERE AND SPECTROPHOTOMETRIC MODELS THAT INCORPORATE NEW DATA FROM OUR PROPOSED LABORATORY SIMULATIONS OF SOLAR WIND ION IRRADIATION OF MERCURY'S REGOLITH SURFACE. CURRENT MODELS TO SIMULATE MERCURY'S EXOSPHERE AND TO ANALYZE SPECTROPHOTOMETRIC DATA OF THE SURFACE MAKE QUESTIONABLE ASSUMPTIONS ABOUT THE SPUTTER YIELD AND SPECTRAL CHANGES FROM ION IRRADIATION. THIS IS DUE TO THE LACK OF EXPERIMENTAL DATA FOR REGOLITH-LIKE LOOSE POWDERS. OUR LABORATORY STUDIES WILL BE THE MOST REALISTIC SIMULATIONS TO DATE FOR THE EFFECTS OF ION IRRADIATION ON REGOLITH-LIKE LOOSE POWDERS AND WILL PROVIDE QUANTITATIVE DATA FOR THE CORRESPONDING SPUTTER YIELD AND SPECTRAL CHANGES. WE WILL INCORPORATE THESE DATA INTO OUR EXOSPHERE AND SPECTROPHOTOMETRIC MODELS AND REINTERPRET ARCHIVAL DATA OF MERCURY. SPECIFIC PLANETARY SCIENCE QUESTIONS THAT WE WILL ADDRESS INCLUDE: (1) WHAT FRACTION OF THE NA EXOSPHERE OF MERCURY IS FORMED BY SOLAR WIND IONS? (2) IS THERE A SYSTEMATIC DIFFERENCE BETWEEN SPUTTERING IN MERCURY'S NORTHERN AND SOUTHERN CUSPS DUE TO THE OFFSET OF ITS DIPOLE MAGNETIC FIELD? (3) CAN ION SPUTTERING EXPLAIN ALL OR ONLY PART OF THE NA LOSS FROM THE PLANET? AND (4) HOW ARE MERCURY'S SPECTROPHOTOMETRIC PROPERTIES ALTERED BY SOLAR WIND IONS? FOR THE LABORATORY PORTION OF THIS WORK WE WILL CONSTRUCT A NOVEL BEAM LINE CONFIGURATION TO IRRADIATE REGOLITH-LIKE LOOSE POWDERS FROM ABOVE AND PERFORM IN-SITU 350-2500 NM SPECTROSCOPIC ANALYSES IN VACUO THEREBY AVOIDING ATMOSPHERIC CONTAMINATION OF THE IRRADIATED SAMPLES. SAMPLES WILL BE PREPARED IN AN INERT ENVIRONMENT TO FURTHER MINIMIZE SURFACE CONTAMINATION BY ATMOSPHERE. WE WILL IRRADIATE THE SAMPLES WITH H+ AND HE+ BEAMS AT TYPICAL SOLAR WIND ENERGIES OF 1 KEV/AMU WHERE AMU IS ATOMIC MASS UNIT. THESE ELEMENTS MAKE UP ~95% AND ~5% OF THE SOLAR WIND RESPECTIVELY. WE KNOW OF NO OTHER LABORATORY IN THE WORLD WITH ALL OF THE ABOVE CAPABILITIES. STATE-OF-THE-ART ION IRRADIATION STUDIES HAVE USED FLAT SURFACES (I.E. SLABS) OR POWDERS WHICH HAVE EITHER BEEN HIGHLY COMPRESSED OR EPOXIED. NONE OF THESE ARE RELIABLE SIMULANTS FOR THE LOOSE POWDERS EXPECTED TO COMPRISE REGOLITHS. MOST PREVIOUS IRRADIATION STUDIES WITH H+ AND HE+ HAVE USED ENERGIES 10-1000 TIMES HIGHER. OTHER HAVE USED IONS OF C N O NE AND AR AT TOO HIGH ENERGIES. THESE ELEMENTS COMPRISE<0.1% OF THE SOLAR WIND AND IT IS UNCLEAR WHETHER THE RESULTS CAN BE RELIABLY SCALED TO H AND HE AT THE RELEVANT ENERGIES. FOR OUR STUDIES SAMPLES WILL BE DERIVED FROM FELDSPARS EXPECTED TO BE COMMON ON THE SURFACE OF MERCURY. BOTH CRYSTALLINE AND GLASS POWDERS WILL BE USED THE LATTER TO ACCOUNT FOR SURFACE VITRIFICATION BY MICROMETEORITE IMPACT VAPORIZATION. SLABS WILL BE USED FOR COMPARISON REFERENCE MEASUREMENTS. OUR PROPOSAL IS RELEVANT TO THE SSW PROGRAM WHICH SOLICITS INNOVATIVE AND INTERDISCIPLINARY STUDIES TO SOLVE KEY SCIENTIFIC QUESTIONS IN THE FIELD. WE WILL ADDRESS (1) THE EVOLUTION AND MODIFICATION OF THE HERMEAN SURFACE AND (2) THE COMPOSITION AND EVOLUTION OF ITS EXOSPHERES ISSUES SQUARELY WITHIN THE SSW SCOPE. PAST PRESENT AND FUTURE MISSIONS FOR WHICH THIS WORK WILL BE RELEVANT INCLUDE MARINER 10 MESSENGER AND BEPICOLOMBO.