SPACE WEATHERING MODIFIES THE CHEMICAL MICROSTRUCTURAL AND SPECTRAL PROPERTIES OF GRAINS ON THE SURFACES OF AIRLESS BODIES AND IS DRIVEN BY MICROMETEORITE IMPACTS AND SOLAR WIND IRRADIATION (HAPKE 2001). OPTICALLY THIS PROCESS CAUSES THE ATTENUATION OF CHARACTERISTIC ABSORPTION BANDS AND REDDENING AND DARKENING OF REFLECTANCE SPECTRA. IN ADDITION TO SPECTRAL CHANGES SPACE WEATHERING CAUSES THE FORMATION OF FE NANOPARTICLES (NPFE) VESICULATED TEXTURES AND AMORPHOUS RIMS ON GRAIN SURFACES. PREVIOUS STUDIES OF RETURNED SAMPLES AND LABORATORY SIMULATIONS OF SPACE WEATHERING PROCESSES HAVE FOCUSED ON THE EFFECTS OF THIS PHENOMENON ON THE SILICATE MINERALS WHICH DOMINATE LUNAR SOILS (E.G. LOEFFLER ET AL. 2016 KELLER ET AL. 1997 NOGUCHI ET AL. 2011). HOWEVER THE SITUATION IS LESS CONSTRAINED FOR MINERALS FOUND ON MORE COMPOSITIONALLY-COMPLEX REGOLITHS E.G. CHONDRITIC BODIES. EXAMPLES OF THESE UNDERSTUDIED MINERALS INCLUDE FE- AND FE-NI SULFIDES (TROILITE PENTLANDITE PYRRHOTITE) AND FE-OXIDES (MAGNETITE). THESE MINERALS HAVE ALL BEEN IDENTIFIED IN RETURNED SAMPLES FROM S-TYPE ASTEROID ITOKAWA IN CARBONACEOUS CHONDRITE METEORITES THOUGHT TO BE ANALOGS OF THE TARGET BODIES OF THE HAYABUSA2 AND OSIRIS-REX MISSIONS OR IN REMOTELY SENSED DATA FROM THESE ASTEROIDS (BLAND ET AL. 2004 NOGUCHI ET AL. 2011 2014 LAURETTA ET AL. 2019). DESPITE THEIR PREVALENCE IN OUR SAMPLE COLLECTION THE PHYSICOCHEMICAL BEHAVIOR OF SULFIDES AND FE OXIDES UNDER SPACE WEATHERING CONDITIONS ARE STILL POORLY UNDERSTOOD. TO BETTER UNDERSTAND THE RESPONSE OF THESE PHASES TO SPACE WEATHERING PROCESSES IN TASK 1 I WILL PERFORM LABORATORY SIMULATIONS OF MICROMETEORITE IMPACTS AND SOLAR WIND IRRADIATION USING PULSED-LASER AND ION-IRRADIATION RESPECTIVELY ON SULFIDE AND FE-OXIDES MINERALS. I WILL THEN USE TRANSMISSION ELECTRON MICROSCOPY (TEM) TO CHARACTERIZE THEIR MICROSTRUCTURAL AND CHEMICAL RESPONSE TO THESE SIMULATED WEATHERING EVENTS. IN TASK 2 I WILL INVESTIGATE THE MICROSTRUCTURAL AND CHEMICAL FEATURES IN NATURALLY SPACE WEATHERED SULFIDE-BEARING GRAINS FROM ASTEROID ITOKAWA RETURNED BY THE HAYABUSA MISSION. I WILL USE ULTRAMICROTOMY AND FOCUSED ION BEAM SCANNING ELECTRON MICROSCOPY (FIB-SEM) TO PREPARE THE SAMPLES FOR ANALYSIS IN THE TEM AND I WILL USE ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDS) TO ANALYZE THEIR CHEMICAL COMPOSITION. COMBINING RETURNED SAMPLE ANALYSES WITH LABORATORY EXPERIMENTS WILL ALLOW ME TO ATTRIBUTE SPECIFIC CHEMICAL AND MICROSTRUCTURAL FEATURES IN NATURALLY SPACE-WEATHERED SAMPLES TO INDIVIDUAL CONSTITUENT PROCESSES. THIS COMPARISON WILL ENABLE ME TO INVESTIGATE THE RELATIVE CONTRIBUTIONS OF MICROMETEORITE IMPACTS AND SOLAR WIND IRRADIATION IN THE SPACE WEATHERING OF ASTEROIDAL REGOLITHS. THE PROPOSED ANALYSES WILL MAXIMIZE THE SCIENTIFIC RETURN OF THE HAYABUSA MISSION AND WILL HELP US PREPARE FOR SAMPLE RETURN FROM THE ONGOING OSIRIS-REX AND HAYABUSA2 MISSIONS. THESE RESULTS WILL ALSO CONTRIBUTE TO A BETTER UNDERSTANDING OF REMOTE SENSING DATA OF AIRLESS BODIES SURFACES AND HELP BUILD A MODEL FOR SPACE WEATHERING ACROSS THE INNER SOLAR SYSTEM. THIS RESEARCH IS DIRECTLY RELEVANT TO THE NASA LABORATORY ANALYSIS OF RETURNED SAMPLES (LARS) PROGRAM AND WILL DIRECTLY ADDRESS SECTION 2 (ORIGIN AND EVOLUTION OF SOLAR SYSTEM BODIES) OF APPENDIX C.18 (NNH19ZDA001N-LARS) OF THE ROSES-2019 NRA. MY GOAL IS TO MAXIMIZE THE SCIENCE DERIVED FROM PLANETARY SAMPLE-RETURN MISSIONS BY PERFORMING DIRECT ANALYSIS OF SAMPLES ALREADY RETURNED TO EARTH SPECIFICALLY WITH PARTICLES COLLECTED BY THE HAYABUSA MISSION