Even if we haven't yet discovered life elsewhere in the cosmos, its basic chemical building blocks appear to be all around us.
The interstellar medium is, by our standards, an exotic physical environment -- lower density than the highest laboratory vacuums, temperatures of about 10 K, and high levels of ionizing UV radiation and energetic cosmic ray particles, to name a few features. By astronomical standards, however, such conditions are relatively mild. So mild, in fact, that they allow for the formation of complex organic molecules that may be essential for the formation of life on terrestrial planets. Observational surveys have detected over 150 molecular species in space (see a running tally here), of which 50 have been classified as complex organics. These contain both fairly familiar species such as acetic acid or acetone and exotic unsaturated species such as HC11N.
We have begun a theoretical study that analyzes state-of-the-art astrochemical reaction networks (such as the UMIST and OSU models) hoping to understand their systems-level features using the tools of network theory. One preliminary finding is that curated astrochemical networks show a scale-free (fractal) topology similar to those seen in complex networks found in biology, engineering, and the social sciences. For example, the UMIST database shows a scale-free topology (shown on the right, only 20% of edges are shown for clarity) with a scaling exponent of 2.45 -- well within the range where interesting scale-free features begin to appear. We are currently developing methods to extract time-dependent graphs from (pseudo-)time-dependent astrochemical simulations, to see how systems-level features of astrochemical systems evolve with time and are affected by environmental parameters.
