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 vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium. and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.