A new astrophysical setting for chondrule formation

Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete va porization of a dusty region of the solar nebula (dust/gas ratio of about 1 0 to 50 times solar). These chondrules formed under oxidizing conditions be fore condensation of iron-nickel metal, at temperatures greater than or equ al to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium. and sul fur. This astrophysical environment is fundamentally different from convent ional models for chondrule formation by localized, brief, repetitive heatin g events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.