SCIENCE GOALS AND OBJECTIVES: SPACE WEATHERING ALTERS THE COMPOSITION MICROSTRUCTURE AND OPTICAL PROPERTIES OF GRAINS ON AIRLESS BODY SURFACES. INVESTIGATING THE EFFECTS OF SPACE WEATHERING IN RETURNED SAMPLES IS CRITICAL FOR UNDERSTANDING THE EVOLUTION OF THE PLANETARY SURFACES FROM WHICH THOSE MATERIALS ARE SOURCED. OUR CURRENT KNOWLEDGE OF SPACE WEATHERING IS CONSTRUCTED FROM A COMBINATION OF RETURNED SAMPLE ANALYSES AND EXPERIMENTS THAT SIMULATE SPACE WEATHERING PROCESSES IN THE LABORATORY. OUR CHARACTERIZATION OF NATURAL SAMPLES HAS LONG FOCUSED ON LUNAR REGOLITHS AND MORE RECENTLY ON GRAINS FROM ASTEROID ITOKAWA. SUCH ANALYSES HAVE CONCENTRATED ON MINERALS THAT DOMINATE LUNAR AND ORDINARY-CHONDRITE REGOLITHS E.G. SILICATES SUCH AS OLIVINE PYROXENE AND PLAGIOCLASE. HOWEVER A KEY GROUP OF MINERALS HAS GONE WITHOUT DETAILED EXAMINATION: SULFIDES. .RECENT EXPERIMENTS PERFORMED BY OUR GROUP AND OTHERS HAVE INDICATED THAT THE MICROSTRUCTURAL AND CHEMICAL RESPONSE OF SULFIDES TO SPACE WEATHERING CONDITIONS DIFFERS SIGNIFICANTLY FROM THEIR SILICATE MINERAL COUNTERPARTS. SIMILARLY THESE EXPERIMENTS SUGGEST THAT SULFIDES PLAY AN IMPORTANT IF NOT DOMINANT ROLE IN THE SPACE WEATHERING OF CARBONACEOUS MATERIALS THAT ARE ANALOGOUS TO SAMPLES WE EXPECT TO RETURN WITH THE OSIRIS-REX AND HAYABUSA2 MISSIONS. IN ORDER TO BETTER UNDERSTAND THE RESPONSE OF SULFIDES TO SPACE WEATHERING WE PROPOSE TO CHARACTERIZE SULFIDE GRAINS FROM ASTEROID ITOKAWA RETURNED BY THE HAYABUSA MISSION. WE WILL PERFORM DETAILED STUDIES OF THE COMPOSITIONAL AND MINERALOGICAL CHANGES IN SULFIDE GRAINS AS A RESULT OF SPACE WEATHERING USING A COMBINATION OF FOCUSED ION BEAM SCANNING ELECTRON MICROSCOPY (FIB-SEM) AND TRANSMISSION ELECTRON MICROSCOPY (TEM). THESE ANALYSES WILL BE COMPLEMENTARY TO OUR ONGOING EXPERIMENTAL STUDIES SIMULATING SPACE WEATHERING OF SULFIDES IN THE LABORATORY. ANALYSES OF THESE SAMPLES WILL NOT ONLY MAXIMIZE THE SCIENTIFIC RETURN OF THE HAYABUSA MISSION BUT WILL ALSO PROVIDE VALUABLE INSIGHT RELEVANT TO THE EVENTUAL ANALYSIS OF RETURNED SAMPLES FROM THE OSIRIS-REX AND HAYABUSA2 MISSIONS. .IN ADDITION TO THE ANALYSES OF SPACE WEATHERED SULFIDES WE PROPOSE TO STUDY IN DETAIL THE MODIFICATION OF SOLAR FLARE TRACKS UNDER DIFFERENT THERMAL CONDITIONS. SOLAR FLARE TRACKS HAVE BEEN RECOGNIZED IN LUNAR SAMPLES AND IN HAYABUSA SAMPLES AND THEIR PRESENCE ENABLES US TO PUT CONSTRAINTS ON THE RESIDENCE TIMESCALES FOR GRAINS IN THE UPPER MM S OF THE REGOLITH ON AIRLESS BODY SURFACES. HOWEVER SOME PROCESSES HAVE BEEN SHOWN TO ALTER AND/OR ERASE THE RECORD OF THESE TRACKS SUCH AS ANNEALING. WE PROPOSE TO PERFORM IN SITU HEATING EXPERIMENTS IN THE TEM USING COMMON PHASES IN RETURNED SAMPLES TO STUDY THE EVOLUTION AND DESTRUCTION OF SOLAR FLARE TRACKS. WE WILL PERFORM BOTH THERMAL SHOCKS AND LONGER DURATION LOW-TEMPERATURE HEATING EVENTS TO UNDERSTAND THE CONDITIONS UNDER WHICH SOLAR FLARE TRACKS ARE ALTERED IN RETURNED SAMPLES. SUCH EXPERIMENTS ARE CRITICAL FOR INTERPRETING ANALYSES OF ALREADY-RETURNED AND FUTURE-RETURNED SAMPLES AND WILL ENABLE AN IMPROVED UNDERSTANDING OF REGOLITH DYNAMICS ON SMALL BODIES SUCH AS ITOKAWA BENNU AND RYUGU. WE ALSO PROPOSE TO SEARCH FOR SOLAR FLARE TRACKS IN RETURNED STARDUST SAMPLES WHICH COULD PROVIDE IMPORTANT INFORMATION ON THE SURFACE RESIDENCE TIMES FOR GRAINS ON COMETS. .RELEVANCE: THE PROPOSED WORK IS DIRECTLY RELEVANT TO THE SCOPE OF THE LABORATORY ANALYSIS OF RETURNED SAMPLES PROGRAM AS IT WOULD INCLUDE DIRECT ANALYSIS OF SAMPLES ALREADY RETURNED TO EARTH AND ADDRESSES THE NASA STRATEGIC OBJECTIVE TO ASCERTAIN THE CONTENT ORIGIN AND EVOLUTION OF THE SOLAR SYSTEM AND THE SCIENCE GOAL TO ADVANCE THE UNDERSTANDING OF HOW THE CHEMICAL AND PHYSICAL PROCESSES IN OUR SOLAR SYSTEM OPERATE INTERACT AND EVOLVE . .