Experiments on Condensation of Calcium Sulfide Grains To Demarcate Environments for the Formation of Enstatite Chondrites

Kaori Yokoyama, Yuki Kimura , and Chihiro Kaito

ACS Earth Space Chem., Article ASAP
DOI: 10.1021/acsearthspacechem.7b00076


“To achieve a better understanding of material evolution in the early solar system, experiments have been performed to constrain the environments in which many of the dust grains formed. Sulfur is an element whose chemical processes and mineralization of related grains are poorly understood. The high reactivity of sulfur makes it difficult to perform experiments in conventional metallic chambers, because these become heavily contaminated. Nevertheless, sulfur is expected to be a key element to understand processes in the early solar system. Here, we performed experiments on the condensation of calcium sulfide (CaS) in a glass chamber in an attempt to identify constraints on the possible formation environments of components of enstatite chondrites in terms of the effects of oxygen. Condensation experiments showed that calcium sulfate (CaSO4) or solid-solution particles of CaS and calcium oxide (CaO), i.e., [Ca(S,O)], were formed at various partial pressures of oxygen. Our results expand the range of possible conditions for the condensation of meteoritic CaS (oldhamite) from a nebula gas and extend the range of environments for the formation of the parent bodies of enstatite chondrites to include those more-oxidizing environments in the solar nebula, where the atomic ratio of oxygen to sulfur was less than 6 and where CaS could have incorporated oxygen to form Ca(S,O) without the formation of CaSO4.”