In search of the molecules of life

The remote detection of a chemical signature of extraterrestrial life ideally requires a broad and nonEarth-centric definition of life. Thus, our proposed approach to detection is based on fundamental thermodynamic assumptions, and some assumptions of how life might obtain energy from its environment. Life, defined as the ability to self-perpetuate, requires a continual input of energy and information. The energy must be tapped in controlled oxidation-reduction reactions between electron donors and acceptors along an electron transport chain. Therefore, the core chemical components of such electron transport chains should be detectable as a signature of life. On Earth, such core structures are principally molecules resembling the porphyrins, quinones, flavins, and nicotinamides (e.g., photosynthetic or respiratory pigments, redox enzymes, and cytochromes). Similar redox-active molecules, perhaps with different structures, might be associated with extraterrestrial life. To validate an approach based on redox signature, signature chemicals were extracted from soil and analyzed by different methods and equipment that may eventually form an integrated laboratory on a chip to be used on other planets or their moons. Its components are a supercritical fluid or solvent extraction module, a separation module, and a detection module with an electrochemical detector and electrospray tandem mass-spectrometer. (C) 2001 Elsevier Science (USA).