Astrochemistry products. Hand holding test tubes containing polycyclic aromatic hydrocarbons (PAHs, structural formulae on labels). PAHs are thought to account for infrared emission bands observed in interstellar dust clouds, and are also thought to be found in comet ices. Experiments exposing PAHs to ultraviolet radiation to simulate conditions in space have produced hydrocarbons that could be precursors to biological molecules. This supports the theories that the origin of life on Earth, and elsewhere in the universe, involved cometary ices impacting planets to deposit organic materials. Photographed at NASA's Ames Research Center, California, USA.