LIKE THE EARTH MERCURY HAS A GLOBAL MAGNETIC FIELD THAT CARVES OUT A CAVITY KNOWN AS THE MAGNETOSPHERE IN THE SOLAR WIND. UNLIKE THE EARTH HOWEVER MERCURY S MAGNETIC FIELD IS ORDERS OF MAGNITUDE WEAKER RESULTING IN A COMPACT MAGNETOSPHERE. OBSERVATIONS FROM THE MARINER 10 FLYBYS OF MERCURY IN 1974 THEREFORE SPARKED BOTH CURIOSITY AND CONTROVERSY AS THE SPACECRAFT DISCOVERED MERCURY S SMALL MAGNETOSPHERE COULD ACCELERATE PARTICLES TO RELATIVISTIC ENERGIES. THE MESSENGER SPACECRAFT WHICH ORBITED THE PLANET FROM 2011 TO 2015 WAS DESIGNED TO DETERMINE THE ORIGIN OF MERCURY S MAGNETIC FIELD THE DRIVERS FOR MAGNETOSPHERIC DYNAMICS AND THE PRIMARY PARTICLE ACCELERATION MECHANISMS. MESSENGER DISCOVERED THAT DUE TO THE PLANET S PROXIMITY TO THE SUN MAGNETIC RECONNECTION DOMINATES THE EFFECTS IN THE MAGNETOSPHERE AND MAY BE RESPONSIBLE FOR PARTICLE ACCELERATION. MAGNETIC RECONNECTION IS THE PROCESS BY WHICH MAGNETIC FIELD LINES BREAK AND RECONFIGURE INTO A LOWER ENERGY STATE CONVERTING MAGNETIC ENERGY INTO PLASMA ENERGY. FOR BOTH PLANETS RECONNECTION OCCURS AT THE DAYSIDE MAGNETOPAUSE THE BOUNDARY SEPARATING THE MAGNETOSPHERE FROM THE SOLAR WIND FLOW AND IN THE MAGNETOTAIL THE STRETCHED MAGNETIC FIELD LINES BEHIND THE PLANET IN THE NIGHTSIDE MAGNETOSPHERE. AT THE EARTH THE FREQUENCY AND INTENSITY OF MAGNETIC RECONNECTION DEPENDS SIGNIFICANTLY ON SOLAR WIND CONDITIONS WHEREAS RECONNECTION AT MERCURY IS MORE INSENSITIVE TO SOLAR WIND CONDITIONS RESULTING IN MORE FREQUENT AND MORE INTENSE RECONNECTION AT MERCURY. WE PLAN TO DISCOVER THE ROLE MAGNETIC RECONNECTION PLAYS IN PLASMA ACCELERATION AND MAGNETOSPHERIC DYNAMICS AT MERCURY BY: (1) DETERMINING THE RELATIONSHIP BETWEEN RECONNECTION AT THE DAYSIDE MAGNETOPAUSE AND THE HOT SOLAR WIND PLASMA THAT REACHES MERCURY S SURFACE AT HIGH LATITUDES (THE CUSPS ); (2) UNDERSTANDING THE CONNECTION BETWEEN ENERGETIC PARTICLE EVENTS AND MAGNETIC RECONNECTION SIGNATURES IN THE MAGNETOTAIL; AND (3) DISCOVERING THE DIFFERENCES BETWEEN EARTH S AND MERCURY S EVENTS OF INTENSE DAYSIDE AND MAGNETOTAIL RECONNECTION KNOWN AS SUBSTORMS. TO ANSWER THESE QUESTIONS WE WILL COMBINE MESSENGER DATA ANALYSIS AND BATSRUS-AMPS MHD-KINETIC MODELING TO GREATLY EXPAND UPON INITIAL STUDIES OF MERCURY S SYSTEM. WE WILL USE WELL-TESTED TECHNIQUES AND MODELING DEVELOPED FOR STUDYING EARTH S MAGNETOSPHERE TO MESSENGER MEASUREMENTS. OUR PROPOSED WORK MEETS PLANETARY SCIENCE S STRATEGIC OBJECTIVES OF UNDERSTANDING HOW PHYSICAL PROCESSES OPERATE AND INTERACT AND OF ENHANCING THE SCIENTIFIC RETURN OF ITS SPACECRAFT MISSIONS. SPECIFICALLY OUR PROPOSED INVESTIGATION WILL HAVE A SIGNIFICANT IMPACT ON THE PLANETARY SCIENCE COMMUNITY BY: (1) ESTABLISHING THE VARIABILITY OF MERCURY S CUSPS AND THEIR RELATION TO MAGNETIC RECONNECTION NEEDED INFORMATION FOR UNDERSTANDING THE COUPLING BETWEEN THE SOLAR WIND MAGNETOSPHERE EXOSPHERE AND SURFACE AT MERCURY; (2) PROVIDING CLOSURE TO OUTSTANDING QUESTIONS ON THE MARINER 10 ENERGETIC PARTICLE BURSTS AND INFORMING THE GENERAL PROCESSES BY WHICH MAGNETOSPHERES CAN PRODUCE ENERGETIC PARTICLES; AND (3) IDENTIFYING IF SUBSTORMS ARE A GENERAL PROCESS BEYOND STRICT TERRESTRIAL-LIKE MAGNETOSPHERES WITH MAGNETOSPHERE-IONOSPHERE COUPLING.