Interstellar graphite in meteorites.

Interstellar graphite in meteorites 

In their continuing search for interstellar "needles" in the meteoritic "haystack," Edward Anders of the University of Chicago and his collaborators have identified tiny grains of graphite, 1 to 4 microns in diameter, in a meteorite known as the Murchison C2 chondrite. Their report appears in the May 17 NATURE. Anders and others had previously reported finding microscopic diamonds and silicon-carbide grains in a number of meteorites (SN: 3/14/87, p.166; 2/7/88, p.7).

Using as evidence the measured ratios of the isotopes carbon-12 and carbon-13 in the graphite grains, the researchers argue tht the graphite may have formed in the outflows from carbon-rich, red-giant stars or in the envelope of matter abruptly expelled when a star rapidly brightens to become a nova. Deposited as particles in interstellar space, the graphite could then be swept up in the processes leading to the formation of a meteorite. It remains unclear, however, why graphite is much less abundant than diamond, wich should be less stable, in the same meteorite.