Exobiochemistry and the Search for Alien Life

Exobiochemistry is the biochemistry of extraterrestrial life. It describes the potential energy and material basis of extraterrestrial life and is needed to guide the search for alien life. The diverse biochemistry of Earth indicates that a wide range of exobiochemistry is possible on other planets. Any exobiochemistry we discover will probably use the same energy sources as Earth's natural biochemistry - light, biological organic material, and more rarely abiotic chemicals. Extraterrestrial life will be based on familiar chemical principles and so will probably capture, store, and release energy using oxidation-reduction reactions similar to those found on Earth. Any extraterrestrial life must produce some chemical indication of its existence. Useful elements will be concentrated, stored, and recycled, altering their availability and isotopic composition. Any significant departure from chemical equilibrium would be good evidence of an exobiochemistry, but an integrated ecological system with interconnected departures from the expected equilibrium would be better. Terrestrial biochemistry provides a basis for generalization and extrapolation but it can not define the limits of exobiochemistry.