Thermodynamic Calculations Support a Rain Cloud Model of Chondrule Formation

Abstract

Thermodynamic calculations using the critically evaluated and optimized FactSage databases lead to the conclusion that chondrules of all types were formed from a “rain cloud” of undercooled liquid oxide droplets that were in equilibrium with the solar nebula. The droplets subsequently solidified rapidly and stochastically in the temperature and pressure gradients of the nebula to form solid chondrules that retained the compositions of the liquid droplets and thereafter were no longer in thermodynamic equilibrium with the nebular gas. This provides a simple unified model for the formation of chondrules in all chondrite meteorites including chondrule-like calcia alumina inclusions, anorthite-rich chondrules, and magnesio-silicate chondrules. Other models of chondrule formation, including the currently favored models of melting of pre-existing solids, are not consistent with thermodynamic calculations.