EARLY SOLAR SYSTEM WATER IN THE LABORATORY

Primitive astromaterials all show some degree of interaction with aqueous fluids, although information such as the location and timing of the aqueous alteration and the detailed nature of the aqueous fluids is lacking. The Monahans (H5) and Zag (H4-6) thermally-metamorphosed ordinary chondrite regolith breccia meteorites contain fluid inclusion-bearing halite (NaCl) and sylvite (KCl) that were incorporated into the H chondrite asteroid after metamorphism and thus have retained direct samples of early solar system water. Solid inclusions in the halites include olivine, Ca-rich pyroxene, feldspars, Fe-Ni metals, sulfides, magnetite, apatite, lepidocrocite, macromolecular carbon, carbonates, graphite, diamond and halogenated methane. The halites resulted from the eruption of subterranean brines from one or more icy early solar system bodies ~4.5 billion years ago. As halite crystallized it entrained organics and mineral grains from the rocky mantle and surface of the body, which was probably the asteroid 1-Ceres. The isotopic composition of the Monahans fluids likely reflects simple water-rock interaction, whereas the Zag water represents mixing of asteroidal and cometary fluids that are believed to have originated in the inner solar nebula and outer solar nebula to molecular cloud, respectively. The intermediate isotope compositions of the halite fluids suggest that accretion and mixing of water of different origins on planetesimals was a fundamental mechanism in the evolution of present planetary water. The halite was subsequently deposited into the regolith of an S-type asteroid (we propose the asteroid 6-Hebe) and later impact events stripped a block of the surface away from this second body, eventually resulting in two meteorite showers on a third body (Earth). We are currently also examining newly-recognized aqueous fluid inclusions in several carbonaceous chondrites. These results document the ubiquity and important role of water in the early solar system, as well as the complex dynamic processes that preserved and eventually delivered samples of these materials to Earth.