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H. C. Connolly Jr., D. S. Burnett (California Institute of Technology)
If it were not for the ubiquitous presence of chondrules and CAIs (Ca-Al-rich inclusions) in chondritic meteorites, astophysical theories for the origin of our solar system would not predict their existence. After fine dust was concentrated relative to gas, it was then melted by some unknown high-temperature energetic process within our protoplanetary nebula to produce mm to cm-sized silicate spheres (chondrules and type B, CAIs) before accretion into kilometer-sized bodies and finally planets. Chondritic materials define the age of our solar system (4.566+2/-1 million years) and the duration of the mechanism which produced them through differences in initial abundance of various isotopes (e.g. Pb, 26Al, etc.). Type B CAIs are the oldest materials, forming some 0.7 to 1 million years before chondrules. The overall duration of chondrule production post-CAI formation lasted for 2-5 million years, almost the lifetime of the nebula. Thus the mechanisms which produced these objects existed from close to the formation of our dust-disk (they define t-start) to near the end of the lifetime of our nebula. A major constraint on the formation of chondrules is that they have been recycled, some experiencing multiple-episodes of heating to different temperatures. Others were fragmented, their pieces incorporated as new precursor material to become relic grains within chondrules. Any potential mechanism for producing these objects either operated repeatedly through the evolution of our disk and/or these objects were transported to a mechanism multiple times. Our new results show that type B CAIs, the largest of these melted spheres, were also partially remelted after their initial formation. Thus the origins of type B CAIs are similar to that of chondrules. Any theoretical model for their origins must include a method for the multiple thermal processing of these objects and relate this process to asteroid and planet formation.