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Presolar Grains (aka Stardust) are the most primitive minerals in the solar system, as their formation predates it. They are minerals thought to have formed in supernovae or the outflows of other suns (such as red giants). Presolar grains typically have distinctive isotopic compositions reflecting their unique and alien birth. Presolar grains include nanodiamonds, graphite, moissanite, titanium carbide, silicon nitride, sapphire, spinel, olivine, and pyroxene, as well as a wide variety of other minerals. See The Evolution of Minerals for a description of why and how the variety of minerals has changed since the beginning of the Solar System. Different groups of presolar grains have distinctive isotopic compositions, suggesting they came from different sources. It seems likely that our solar system condensed from a giant molecular cloud which had multiple sources, and which was not well-mixed. The often unusual minerals of presolar grains are likely indicative of the unique sources. Remember that, as a whole, the baryonic universe consists of 96% hydrogen plus traces of everything else, such that the most common chemicals are all hydrides: OH2, NH3, CH4, etc.. But conditions are different in a Red Giant, which burns Helium into Carbon, or Carbon into Oxygen, or Oxygen into heavier elements, up to and including iron and nickel. The relative elemental presence and hot, dense atmospheres of Red Giants can allow super-refractory minerals to condense, and these minerals can be carried away in the strong stellar winds which themselves are the sources of more minerals. Conditions in a supernova are especially unusual. The extreme high energies and high neutron fluxes together create unusual isotopes, some of which are stable enough to form minerals with whatever happens to be nearby, and in a supernova that can be anything. |
