Chemical Processes in the Interstellar Medium: Source of the Gas and Dust in the Primitive Solar Nebula

Everything that became part of the primitive solar nebula first passed through the interstellar medium and the dense molecular cloud from which the nebula collapsed. We begin with a brief discussion of the connection between dense molecular clouds and the formation of solar-type stars. We then review processes that occur in these environments in order to constrain the chemical and physical properties of the matter that might still be preserved in primitive meteorites and that was the source material for every asteroid, comet, moon, and planet that exists at the present time in our own or in any other planetary system. Much of this history may be completely overprinted via processes occurring in the nebula itself or in larger planetary bodies, yet some signatures, such as those carried by isotopes of H, O, or N can be much more persistent.