Condensation of Rocky Material in Astrophysical Environments

Abstract

Volatility-dependent fractionation of the rock-forming elements at high temperatures is an early, widespread process during formation of the earliest solids in protoplanetary disks. Equilibrium condensation calculations allow prediction of the identities and compositions of mineral and liquid phases coexisting with gas under presumed bulk chemical, pressure, and temperature conditions. A graphical survey of such results is presented for systems of solar and nonsolar bulk composition. Chemical equilibrium was approached to varying degrees in the local regions where meteoritic chondrules, Ca-Al-rich inclusions, matrix, and other components formed. Early, repeated vapor-solid cycling and homogenization, followed by hierarchical accretion in dust-rich regions, is hypothesized for meteoritic inclusions. Disequilibrium chemical effects appear to have been common at all temperatures, but increasingly so in lessrefractory meteoritic components. Work is needed to better model high-temperature solid solutions, indicators of these processes.