In dense molecular clouds, the birthplace of stars and planets, interstellar atoms andmolecules freeze onto extremely cold dust and ice particles. These ices are processed byultraviolet light and cosmic rays forming hundreds of far more complex species, some ofastrobiological interest. Eventually, these rain down on primordial planets where theytake part in the young chemistry on these new worlds.

Although the IR spectroscopy and energetic processing of interstellar ice analogs havebeen studied for nearly 30 years, similar studies of PAH containing ices have only justbegun. This paper presents recent results from laboratory studies on the vacuumultraviolet (VUV) photochemistry of PAHs in water ice at low temperatures to assess theroles they play in the photochemical evolution of interstellar ices and their relevance toastrobiology. A number of “surprises” were found in these studies on PAH containingwater-rich ices, indicating that PAHs likely play very important, unexpected roles incosmic ice chemistry, physics and astrobiology.