THE EVOLUTION OF INTERSTELLAR ICES NEAR YOUNG STELLAR OBJECTS

Introduction: The spectral features of interstellar ices yield both quantitative information on abundances and insight into the environments in which the ices form and evolve. A detailed study is in progress of the solid CO 2 infrared vibrational bending-mode absorption at 15 μm, using spectra acquired by the Spitzer Space Telescope, in coordination with ground-based data for other major ice constituents, notably H2O and CO. Studies of CO 2 are important to astrobiology for two primary reasons. First, the abundance of CO 2 relative to other C-bearing species is an important diagnostic of chemical evolution toward molecular complexity in the interstellar medium, because CO 2 production (by oxidation of CO) competes directly for the available carbon with hydrogenation reactions that produce organic molecules such as H 2 CO, CH 3 OH and HCOOH. Second, the profile of the 15 μm feature provides insight into physical conditions, as it is sensitive to the temperature, crystallinity and structure of the icy matrix that contains the CO 2 . This paper presents a summary of recent and ongoing work. Results for cold, quiescent regions of molecular clouds are compared with those for the environs young stellar objects (YSOs) where the ices are subject to thermal processing. The ternary plot is used as an analytical tool.