THE PRIMARY OBJECTIVE OF THIS PROPOSAL IS TO UNDERSTAND THE BEHAVIOR OF FE AND SI ISOTOPES DURING PLANETARY ACCRETION AND DIFFERENTIATION. THE PROPOSED WORK WILL INVESTIGATE AND DETERMINE IF THE PROCESSES OF PLANETARY ACCRETION AND DIFFERENTIATION UNDER VARIABLE REDOX CONDITIONS ARE RESPONSIBLE FOR MASS-DEPENDENT FE AND SI ISOTOPE FRACTIONATION OBSERVED IN A RANGE OF PLANETARY MATERIALS. WE PROPOSE TO USE A VARIETY OF ANALYTICAL TECHNIQUES TO ADDRESS OUR RESEARCH OBJECTIVES. SPECIFICALLY WE WILL CONDUCT INITIAL CHARACTERIZATION OF A VARIETY OF CHONDRITIC AND ACHONDRITIC METEORITES (RECORDING VARIABLE DEGREES OF DIFFERENTIATION AND REDOX CONDITIONS) USING EMPA AT THE LEROY EYRING CENTER FOR SOLID STATE SCIENCE AT ASU. WE WILL ALSO CONDUCT COMBINED FE AND SI ISOTOPIC INVESTIGATIONS OF PHASE SEPARATES AND BULK SAMPLES OF SUCH METEORITES USING THERMO-NEPTUNE MC-ICPMS IN THE ISOTOPE COSMOCHEMISTRY AND GEOCHRONOLOGY LABORATORY (ICGL) AT ASU. THE OBJECTIVE OF THIS STUDY ALIGNS WITH OBJECTIVE 1.5 OF 2014 NASA STRATEGIC PLAN TO "ASCERTAIN THE CONTENT ORIGIN AND EVOLUTION OF THE SOLAR SYSTEM AND THE POTENTIAL FOR LIFE ELSEWHERE". SPECIFICALLY THE PROPOSED WORK WILL ADDRESS NASA'S PLANETARY SCIENCE GOALS AS DESCRIBED IN CHAPTER 4.3 OF THE SCIENCE MISSION DIRECTORATE 2014 SCIENCE PLAN "ADVANCE THE UNDERSTANDING OF HOW THE CHEMICAL AND PHYSICAL PROCESSES IN THE SOLAR SYSTEM OPERATE INTERACT AND EVOLVE"