Meteoritic evidence that graphite is rare in the interstellar medium

Abstract

This letter discusses the carbonaceous material from several distinct astrophysical environments that has been identified in primitive meteorites. Most of this material is not well-crystallized graphite, but ranges from kerogen-like macromolecular organic matter to poorly graphitized carbon. Of the small fraction of the carbonaceous material which is graphite, most of this may have resulted from the graphitization of macromolecular precursors in the solar nebula. Since graphite is more stable than those precursors, pre-existing interstellar graphite should have survived in meteorites to at least the same extent as did other forms of carbon. I conclude from this dearth of graphite that graphitic carbon was not a major component of the interstellar dust at the time of the formation of the Solar System.