The chondrules, calcium-aluminum-rich inclusions (CAIs), and rims in chondritic meteorites could be formed when solid bodies are lifted by the aerodynamic drag of a magnetocentrifugally driven wind out of the relative cool of a shaded disk close to the star into the heat of direct sunlight. For reasonable self-consistent parameters of the bipolar outflow, the base and peak temperatures reached by solid bodies resemble those needed to melt CAIs and chondrules. The process also yields a natural sorting mechanism that explains the size distribution of CAIs and chondrules, as well as their fine-grained and coarse-grained rims. After reentry at great distances from the original launch radius, the CAIs, chondrules, and their rims would be compacted with the ambient nebular dust comprising the matrices, forming the observed chondritic bodies.

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Protostars emit more x-rays, hard and soft, than young sunlike stars in more advanced stages of formation. The x-ray emission becomes harder and stronger during flares. The excess x-rays may arise as a result of the time-dependent interaction of an accretion disk with the magnetosphere of the central star. Flares produced by such fluctuations have important implications for the x-wind model of protostellar jets, for the flash-heating of the chondrules found in chondritic meteorites, and for the production of short-lived radioactivities through the bombardment of primitive rocks by solar cosmic rays.

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We report the discovery of a large anomaly in the isotopic composition of Mg in a Ca‐Al rich chondrule from the Allende meteorite. This anomaly is manifest independently of instrumental fractionation and is due to an enrichment of about 1.3 percent in 26Mg while the abundances of 25Mg and 24Mg are terrestrial in value. There is a strong correlation in this chondrule between the 26Mg excess and the Al/Mg ratio so that the most plausible cause of the anomaly is the in situ decay of now extinct 26Al (τ½ = 0.72 × 106 yr). Mineral phases extracted from a Ca‐Al‐rich aggregate have distinct Al/Mg but show identical, small Mg anomalies which are apparent after correction for fractionation (δ26Mg = 0.3%). These data indicate that this aggregate was isotopically homogenized in a high Al/Mg environment after the decay of 26Al had occurred or that some of the Mg anomalies are due to effects other than in situ decay of 26Al.

Two explanations exist for the short-lived radionuclides (T 1/2 5 Myr) present in the solar system when the calcium-aluminum-rich inclusions (CAIs) first formed. They originated either from the ejecta of a supernova or by the in situ irradiation of nebular dust by energetic particles. With a half-life of only 53 days, 7 Be is then the key discriminant, since it can be made only by irradiation. Using the same irradiation model developed earlier by our group, we calculate the yield of 7 Be. Within model uncertainties associated mainly with nuclear cross sections, we obtain agreement with the experimental value. Moreover, if 7 Be and 10 Be have the same origin, the irradiation time must be short (a few to tens of years), and the proton flux must be of order F $ 2 ; 10 10 cm À2 s À1 . The X-wind model provides a natural astrophysical setting that gives the requisite conditions. In the same irradiation environment, 26 Al, 36 Cl, and 53 Mn are also generated at the measured levels within model uncertainties, provided that irradiation occurs under conditions reminiscent of solar impulsive events (steep energy spectra and high 3 He abundance). The decoupling of the 26 Al and 10 Be observed in some rare CAIs receives a quantitative explanation when rare gradual events (shallow energy spectra and low 3 He abundance) are considered. The yields of 41 Ca are compatible with an initial solar system value inferred from the measured initial 41 Ca / 40 Ca ratio and an estimate of the thermal metamorphism time (from Young et al.), alleviating the need for two-layer proto-CAIs. Finally, we show that the presence of supernova-produced 60 Fe in the solar accretion disk does not necessarily mean that other short-lived radionuclides have a stellar origin.