OBJECTIVES: THE OVERARCHING OBJECTIVE OF THE RESEARCH OUTLINED IN THIS PROPOSAL IS TO ELUCIDATE THE PROCESSES THAT LEAD ULTIMATELY TO FORMATION OF EARTH AND OTHER TERRESTRIAL-LIKE PLANETS IN THE SOLAR SYSTEM. OUR PRIMARY FOCUS WILL BE ON THE SORTING OF ELEMENTS AND THEIR ISOTOPES BY THEIR RELATIVE VOLATILITIES. TWO PROJECTS ARE PROPOSED: 1) EXPERIMENTS SIMULATING THE CHEMICAL AND ISOTOPIC EFFECTS OF COLLISION-INDUCED MELTING OF PLANET PRECURSORS; AND 2) EXPLICATION OF POSSIBLE CRYSTAL CHEMICAL CONTROLS ON HIGH-PRECISION OXYGEN ISOTOPE RATIOS THAT COULD INFLUENCE OUR INTERPRETATIONS OF THESE DATA IN EXTRATERRESTRIAL SAMPLES. APPROACH: FOR THE FIRST PROJECT (THE LARGEST OF THE TWO) THEIR APPROACH IS TO TEST THE EMERGING HYPOTHESIS THAT THE ISOTOPIC COMPOSITIONS OF ROCKY BODIES IN THE SOLAR SYSTEM ARE THE RESULT OF COLLISIONS. THEY PROPOSE A PROGRAM OF EXPERIMENTS TO MEASURE THE CHEMICAL AND ISOTOPIC CONSEQUENCES OF MELTING AND EVAPORATION USING CHONDRITIC STARTING MATERIALS. THE GOAL IS TO ASSESS THE MEANING OF HEAVY ISOTOPE ENRICHMENT OF MODERATELY REFRACTORY ELEMENTS IN ROCKY SOLAR SYSTEM BODIES BY CALIBRATING SELF-CONSISTENT MODELS FOR ISOTOPE FRACTIONATION DURING EVAPORATION. EXPERIMENTS WILL BE PERFORMED BY HEATING SAMPLES WITH AN INFRARED LASER AS THEY ARE AERODYNAMICALLY LEVITATED IN A GAS OF CONTROLLED COMPOSITION. BULK CHEMICAL COMPOSITIONS AND ISOTOPE RATIOS FOR SI MG FE AND O WILL BE MEASURED IN THE EVAPORATIVE RESIDUES PRODUCED UNDER A VARIETY OF CONDITIONS (E.G. DIFFERENT VALUES FOR FO2). RESULTS FROM THESE EXPERIMENTS CAN BE USED TO TEST QUANTITATIVELY THE HYPOTHESIS THAT EVAPORATION DURING COLLISIONS WAS THE PRIMARY CONTROL ON THE ISOTOPIC COMPOSITIONS OF SI MG FE AND O (MASS DEPENDENT ONLY) COMPRISING EARTH MARS VESTA AND OTHER BODIES. FOR THE SECOND PROJECT THEY PLAN TO FOLLOW UP ON OUR EARLIER STUDIES OF LUNAR HIGHLAND ROCKS SHOWING THAT THESE SAMPLES HAVE CURIOUSLY LOW MASS-INDEPENDENT OXYGEN ISOTOPE SIGNALS COMPARED WITH LUNAR BASALTS. THEY HAVE FOUND A CORRELATION BETWEEN SIGNALS OF THIS NATURE IN TERRESTRIAL ANALOGS AND CRYSTAL CHEMICAL PARAMETERS INCLUDING BULK MODULUS AND THERMAL EXPANSIVITY. IF THIS OXYGEN ISOTOPE SIGNAL IS CRYSTAL CHEMICAL IT PLACES A LIMIT ON THE USEFULNESS OF ULTRA-HIGH-PRECISION OXYGEN ISOTOPE RATIO MEASUREMENTS AS A MEANS FOR IDENTIFYING DISTINCT SOURCES OF OXYGEN IN EXTRATERRESTRIAL SAMPLES. ULTRA-HIGH-PRECISION OXYGEN ISOTOPE RATIO MEASUREMENTS IN LUNAR AND TERRESTRIAL MINERALS REPRESENTING DIFFERENT STRUCTURES (E.G. ORTHOSILICATES VS. TECTOSILICATES) ARE PLANNED TO RESOLVE THIS ISSUE. RELEVANCE TO EMERGING WORLDS: THE EMERGING WORLDS PROGRAM HAS THE STATED GOAL OF FOSTERING OUR UNDERSTANDING OF THE FORMATION AND EARLY EVOLUTION OF THE SOLAR SYSTEM INCLUDING THE FORMATION AND EVOLUTION OF PLANET PRECURSORS. THEIR WORK IS DIRECTED TOWARDS ACHIEVING A FULLER UNDERSTANDING OF HOW ROCKY BODIES ACQUIRED THEIR CHEMICAL AND ISOTOPIC CHARACTERISTICS AND SO IS RELEVANT TO THE GOALS OF THE PROGRAM.