Sulfur chemistry in protoplanetary nebulae with time-varying oxygen abundances

Chemical models of solar nebula chemistry are presented which show the influence of progressive water depletion from the inner solar nebula. The main focus of this work is the equilibrium distribution of S resulting from this process. Under canonical solar nebula conditions, H ₂ S is the dominant S-bearing species in the gas phase and troilite (FeS) is the primary reservoir for S after condensation. As water vapor diffuses out to its condensation front, the equilibrium distribution of S changes significantly. With the removal of water vapor, SiS becomes the most abundant S-bearing gas and MgS and CaS compete with FeS as the main sulfide reservoir. These results allow us to argue that some of the minerals in the enstatite chondrites formed through the heterogeneities associated with the nebular ice condensation front, and that the sulfur abundance in Jupiter reflects a depletion in H ₂ S that is the result of inner nebula sulfur chemistry under varying oxygen abundance.