Search Parameters for the Remote Detection of Extraterrestrial Life

Direct consequences of biological activity (biosignatures) are currently known only for the planet Earth. However, geophysical characteristics consistent with conditions conducive for life (geoindicators) are remotely detectable by robotic technology at a number of sites in the solar system, where conditions compatible with the support of life may exist. By focusing on a search for energy gradients, complex chemistry, liquids that may act as solvents, atmospheres, and indicators of geological differentiation, robotic exploration of the solar system and beyond should lead to fruitful targets in the search for extraterrestrial life. A combination of various techniques is especially useful to detect promising sites. For example, information on complex chemistry can be obtained by molecular absorption spectra, surface reflectance spectra, imaging spectroscopy, polarimetry, radar measurements, detection of alteration minerals and gradients in surface coloration. An analysis of all major solar system bodies for geoindicators of life to date suggests that Mars, Titan, and the Galilean satellites should be given the highest priority in the search for extraterrestrial life in our solar system, but Triton, Titania, Enceladus, and Iapetus, among others, are also worthy of greater attention.