PROTOSTELLAR COSMIC RAYS AND EXTINCT RADIOACTIVITIES IN METEORITES

[[abstract]]Calcium-aluminumÈrich inclusions (CAIs) and chondrules of chondritic meteorites may originate with the melting of dustballs launched by a magnetically driven bipolar outÑow from the inner edge of the primitive solar nebula. Bombardment by protostellar cosmic rays may make the rock precursors of CAIs and chondrules radioactive, producing radionuclides found in meteorites that are difficult to obtain with other mechanisms. Reasonable scalings from the observed hard X-rays for the cosmic-ray protons released by Ñares in young stellar objects yield the correct amounts of 41Ca, 53Mn, and 138La inferred for meteorites, but proton- and a-induced transformations underproduce 26Al by a factor of about 20. The missing 26Al may be synthesized by 3He nuclei accelerated in impulsive Ñares reacting primarily with 24Mg, an abundant isotope in the target precursor rocks. The mechanism allows a simple explanation for the very di†erent ratios of 26Al/27Al inferred for normal CAIs, CAIs with fractionated and unidentiÐed nuclear (FUN) anomalies, and chondrules. The overproduction of 41Ca by analogous 3He reactions and the case of 60Fe inferred for eucritic meteorites require special interpretations in this picture.[[fileno]]2010507010018[[department]]天文