PAHs and Astrobiology

In dense molecular clouds, the birthplace of stars and planets, interstellar atoms and molecules freeze onto extremely cold dust and ice particles. These ices are processed by ultraviolet light and cosmic rays forming hundreds of far more complex species, some of astrobiological interest. Eventually, these rain down on primordial planets where they take part in the young chemistry on these new worlds. Although the IR spectroscopy and energetic processing of interstellar ice analogs have been studied for nearly 30 years, similar studies of PAH containing ices have only just begun. This paper presents recent results from laboratory studies on the vacuum ultraviolet (VUV) photochemistry of PAHs in water ice at low temperatures to assess the roles they play in the photochemical evolution of interstellar ices and their relevance to astrobiology. A number of “surprises” were found in these studies on PAH containing water-rich ices, indicating that PAHs likely play very important, unexpected roles in cosmic ice chemistry, physics and astrobiology.