The nature and evolution of interstellar ices.

The evolution of icy grain mantles is governed by the environment in which they exist. This review presents an overview of the study of the molecules that make up the mantles and discusses their relevance to the origin of life. Models predict two phases of mantle growth during cloud collapse: simple polar and nonpolar molecules dominate the mantle layers at early and late times, respectively (Section 1). The effect of processing on grain mantle composition and the connection between organics in grain mantles and prebiotic chemistry is introduced. Section 2 describes how infrared spectroscopy of dense cloud sources, combined with theoretical models and laboratory data, gives us information on the composition and abundance of the ices in varying regions. The observed features and how they are used as diagnostics of mantle evolution are discussed in Section 3. This section also discusses the importance of these molecules to prebiotic chemistry. Section 4 compares grain mantle composition in different low-mass star forming regions, which best represent the solar birthplace. The final section (Section 5) summarizes the information presented, emphasizing the link between the study of interstellar dust and the origin of life.