The possibilities for detecting non-terrestrial biological material are briefly reviewed in light of the flurry of extrasolar planet detections over the last ten years and the forthcoming space missions designed to search for signs of extraterrestrial life. We summarize the evidence for non-terrestrial organic material and the challenges involved in the development of robust and reliable biosignatures, i.e. features whose presence requires a biological origin. It is necessary to distinguish between prebiotic material, which is likely to be a necessary precursor to life but which is not produced by a biological system, and the detection of either biological material itself or its effect on the environment. We discuss the use of chirality and spectrally resolved circular polarization as a remote-sensing technique for distinguishing between biological and non-biological substances.Peer reviewe
