INTERSTELLAR MATTER IN METEORITES

The solar system is much younger than the universe (only 4. 5 billion years compared with 10 to 15 billion years), and so it must have formed from older matter that had a previous history. The first hint of presolar matter came in 1969, when David C. Black and Robert O. Pepin of the University of Minnesota studied the isotopic composition of the noble (chemically inert) gas neon in carbonaceous chondrites: dark gray, rather nondescript-looking stones that are the most primitive meteorites known. Carbonaceous chondrites incorporate material originating outside the solar system, including matter expelled by supernovas and other stars. In the course of this article four types of exotic carbon in primitive meteorites are discussed; three are forms of elemental carbon carrying neon E(L), xenon HL and s xenon, and the fourth is a polymer enriched in deuterium.