THE INVENTORY OF INTERSTELLAR MATERIALS AVAILABLE FOR THE FORMATION OF THE SOLAR-SYSTEM

Tremendous progress has been made in the field of interstellar dust in recent years through the use of telescopic observations, theoretical studies, laboratory studies of analogs, and the study of actual inters tellar samples found in meteorites. It is increasingly clear that the interstellar medium (ISM) contains an enormous diversity of materials created by a wide range of chemical and physical processes. This under standing is a far cry from the picture of interstellar materials held as recently as two decades ago, a picture which incorporated only a fe w generic types of grains and few molecules. In this paper, I attempt to review some of our current knowledge of the more abundant materials thought to exist in the ISM. The review concentrates on matter in int erstellar dense molecular clouds since it is the materials in these en vironments from which new stars and planetary systems are formed. Howe ver, some discussion is reserved for materials in circumstellar enviro nments and in the diffuse ISM. The paper also focuses largely on solid materials as opposed to gases since solids contain a major fraction o f the heavier elements in clouds and because solids are most likely to survive incorporation into new planetary systems in identifiable form . The paper concludes with a discussion of some of the implications re sulting from the recent growth of our knowledge about interstellar mat erials and also considers a number of areas in which future work might be expected to yield important results.