Volatile element chemistry in the solar nebula: Na,K, F,Cl, Br,and P

The results of the most extensive set to date of thermodynamic calculations of the equilibrium chemistry of several hundred compounds of the elements Na, K, F, Cl, Br, and P in a solar composition system are reported. The calculations are carried out over a wide range of temperatures and pressures and along an adiabat in the primitive solar nebula. Two extreme models of accretion are investigated. In one extreme complete chemical equilibrium between condensates and gases is maintained because the time scale for accretion is long compared to the time scale for cooling or dissipation of the nebula. Condensates formed in this homogeneous accretion model include several phases such as whitlockite, alkali feldspars, and apatite minerals which are found in chondrites. In the other extreme complete isolation of newly formed condensates from prior condensates and gases occurs due to a time scale for accretion that is short relative to the time required for nebular cooling or dissipation. The condensates produced in this heterogeneous accretion model include alkali sulfides, ammonium halides, and ammonium phosphates. None of these phases are found in chondrites. Available observations of the Na, K, F, Cl, Br, and P elemental abundances in the terrestrial planets are found to be compatible with the predictions of the homogeneous accretion model.