MERCURY S GLOBAL-SCALE MAGNETIC FIELD IS UNIQUE AMONG SUCH FIELDS IN OUR SOLAR SYSTEM. MESSENGER DATA HAVE SHOWN THAT IT IS AXIALLY SYMMETRIC WITH RESPECT TO THE PLANET S ROTATIONAL AXIS BUT ASYMMETRIC WITH RESPECT TO ITS GEOGRAPHICAL EQUATOR AND IS ABOUT 100 TIMES WEAKER THAN EARTH S FIELD. THIS FIELD IS MODULATED BY A SMALL ANNUAL INDUCTION SIGNAL AS A RESULT OF MERCURY S ECCENTRIC ORBIT. MESSENGER DATA TAKEN BELOW ~100 KM ALTITUDE ALSO LED TO THE DISCOVERY OF VERY WEAK LITHOSPHERIC MAGNETIC FIELDS. THESE SIGNALS ARE PARTICULARLY DOMINANT AROUND THE CALORIS IMPACT BASIN BUT ALSO OCCUR IN SOME SMALLER IMPACT BASINS. THESE LITHOSPHERIC FIELDS REFLECT THE PRESENCE OF MAGNETIZED ROCKS AND CALCULATIONS SHOW THAT AT LEAST SOME OF THAT MAGNETIZATION WAS ACQUIRED IN AN ANCIENT (>3 GYR OLD) FIELD. IMPROVED KNOWLEDGE OF THE CORE FIELD IS NEEDED TO STUDY THE INTERNAL STRUCTURE OF THE PLANET BUT ALSO TO MAKE FUNDAMENTAL PROGRESS IN UNDERSTANDING THE LITHOSPHERIC FIELD BECAUSE THE CORE FIELD AND MAJOR MAGNETOSPHERIC FIELDS MUST BE SUBTRACTED FROM THE OBSERVATIONS TO REVEAL THE LITHOSPHERIC SIGNALS. TO DATE LITTLE IS KNOWN ABOUT THE DEPTHS OF LITHOSPHERIC MAGNETIZATION AND THE PROCESSES RESULTING IN ITS OBSERVED SPATIAL DISTRIBUTION. FOR EXAMPLE WHETHER THE MAGNETIZATION RESIDES PRIMARILY WITHIN THE CRUST OR EXTENDS INTO THE MANTLE IS UNKNOWN BUT HAS IMPORTANT IMPLICATIONS FOR THE TYPES AND DISTRIBUTIONS OF MAGNETIC MINERALS. FURTHERMORE WAVELENGTHS IN THE LITHOSPHERIC FIELD OF SEVERAL HUNDRED TO A FEW THOUSAND KM ARE CURRENTLY UNCONSTRAINED. WE AIM TO ANSWER THE FOLLOWING QUESTIONS: (1) WHAT IS THE TIME-AVERAGED NON-DIPOLAR STRUCTURE IN THE CORE FIELD? (2) WHAT CONSTRAINTS CAN THIS PROVIDE ON THE DYNAMO REGION INCLUDING (I) ITS DEPTH WITHIN THE OUTER CORE (II) THE ROLE OF THE INNER CORE AND CORE-MANTLE BOUNDARY ON THE DYNAMO? (3) WHAT ARE THE SPATIAL PATTERNS IN AND INTENSITY OF THE LITHOSPHERIC MAGNETIC FIELD AT THE PLANETARY SURFACE? (4) WHAT MECHANISMS LED TO THESE AND WHAT CONSTRAINTS DO THE RESULTS PLACE ON THE INTENSITY OF MERCURY'S CORE FIELD EARLIER IN THE PLANET'S HISTORY? WE WILL CALCULATE CORE-FIELD MODELS (QUESTION 1) BY INVERTING FOR A LARGE-SCALE INTERNAL-SOURCE REGIONAL SPHERICAL-HARMONIC MODEL USING DATA FROM MAGNETICALLY QUIET ORBITS AND ACCOUNTING FOR EXTERNAL MAGNETOSPHERIC FIELDS. IN PARTICULAR TO DISCRIMINATE BETWEEN CONTRIBUTIONS FROM CORE-FIELD AND FIELD-ALIGNED CURRENTS WE WILL ESTIMATE AND SUBTRACT THE LATTER IN THE LOCAL TIME FRAME. THE CORE-FIELD MODELS AND THEIR SPHERICAL-HARMONIC SPECTRA PROVIDE CONSTRAINTS ON THE DYNAMO PROCESS ADDRESSING QUESTION (2). DETAILED LITHOSPHERIC MAGNETIC FIELD MODELS EVALUATED ON THE PLANET'S SURFACE WILL USE A RECENTLY DEVELOPED LOCALIZED SPHERICAL-HARMONIC APPROACH AFTER ACCOUNTING FOR CORE AND MAGNETOSPHERIC FIELDS (QUESTION 3). THE DISTRIBUTION OF MAGNETIZATION AND CONSTRAINTS ON MAGNETIZATION DEPTHS WILL BE INFERRED FROM THE RESULTING MODELS AND THE RELATIVE CONTRIBUTIONS OF INDUCED VS. REMANENT MAGNETIZATION QUANTIFIED FOR DIFFERENT MAGNETIC CARRIERS. THIS WILL ULTIMATELY PROVIDE CONSTRAINTS ON THE MECHANISMS OF MAGNETIZATION ACQUISITION AND THE ANCIENT CORE FIELD INTENSITY (QUESTION 4). MERCURY IS THE ONLY TERRESTRIAL PLANET BESIDES EARTH WITH AN ACTIVE CORE FIELD. UNDERSTANDING MERCURY'S PRESENT DYNAMO FIELD AND THE RECORD OF LITHOSPHERIC MAGNETIZATION IS KEY FOR CONSTRAINING CORE FIELD EVOLUTION MODELS WHICH IN TURN HELPS UNDERSTAND THE CHANCES FOR SURFACE HABITABILITY ON TERRESTRIAL PLANETS OUTSIDE OF OUR SOLAR SYSTEM. UNDERSTANDING THE MECHANISMS THAT CREATED THE LITHOSPHERIC MAGNETIC FIELD ON MERCURY WILL HELP US UNDERSTAND SIMILAR MECHANISMS ON OTHER TERRESTRIAL PLANETARY BODIES SUCH AS MARS AND THE MOON. THIS RESEARCH CONTRIBUTES DIRECTLY TO OBJECTIVE 1.5 OF NASA'S 2014 STRATEGIC PLAN. THE PROPOSED WORK WILL USE MESSENGER MAGNETIC FIELD DATA ARCHIVED IN THE PDS AND IS THUS RELEVANT TO THE DDAP SOLICITATION.