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F. H. Shu (Univ. of California, Berkeley)
The existence of chondritic meteorites has posed deep puzzles for our understanding of the origin of the solar system for two hundred years. Chondrites are believed to be primitive material that recorded the physical conditions under which solids in the solar nebula aggregated to form the interiors of the terrestrial planets and the cores of the giant planets. Chondritic meteorites contain a grainy matrix that has obviously never been heated to more than a few hundred K, intimately mixed with mm- to cm-sized balls of rock that have been brought briefly (hours for chondrules to days for refractory inclusions) to the melting temperatures of iron-magnesium silicates or calcium-aluminum silicates and oxides. Moreover, the calcium-aluminum-rich inclusions (CAIs) contain evidence for short-lived radioactivities that should have been long extinct at the birth of the sun and its planets, and yet were clearly alive at the origin of the meteoritical parent bodies. According to modern astronomical observations and theory, the solar nebula was not nearly hot enough to melt rocks at the distance of the asteroid belt where the parent bodies of meteorites reside, nor are time scales as short as hours to days natural for such regions. I will review a new theory developed by our group which suggests that chondrules and CAIs originated much closer to the protosun, and that they were irradiated by protosolar flares and cosmic-ray particles in the fierce interaction region between a strongly magnetized protosun and its surrounding protoplanetary disk, before being thrown to the distances of their modern host bodies by a powerful bipolar jet that is another byproduct of this interaction. I will present evidence unearthed since the initial development of the theory that supports its assumptions and conclusions, and I will conclude with some brief remarks about the changes brought to the question of our astronomical origins by the new perspective. This work was funded by NASA's program on Origins of Solar Systems.