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The ancestor philosophers' dream of thousands of new worlds is finally realised: about 3500 extrasolar planets have been discovered in the neighborhood of our Sun. Most of them are very different from those we used to know in our Solar System. Others orbit their parent star inside the belt known as Habitable Zone (HZ) where a rocky planet with the appropriate climate could have the availability of liquid water on its surface. Those planets, in HZ or not, will be the object of observation that will be performed by new space- and ground-based instrumentation. Space missions, such as JWST and the very recently proposed ARIEL (ESA M-Class Mission), or ground based instruments, like SPHERE@VLT, GPI@GEMINI and EPICS@ELT, have been proposed and built to measure the atmospheric transmission, reflection and emission spectra over a wide wavelength range. Exoplanets are unique objects in astronomy because they have local counterparts the Solar System planets available for comparative planetology studies, but there are also really interesting outsider cases like super Earths. In our own system, proto-planet evolution was flanked by an active prebiotic chemistry that brought about the emergency of life on the Earth. The search for life signatures requires as the first step the knowledge of planet atmospheres, main objective of future exoplanetary space explorations. Indeed, the quest for the determination of their chemical composition is of much larger value than suggested by the specific case. It opens out to the more general speculation on what such detection might tell us about the presence of life on those planets. As, for now, we have only one example of life in the universe, we are bound to study terrestrial organisms to assess possibilities of life on other planets and guide our search for possible extinct or extant life on other planetary bodies. The planet atmosphere characteristics and possible biosignatures will be inferred by studying such composite spectrum in order to identify the emission/absorption lines/bands from atmospheric molecules as water (H2O), carbon monoxide (CO), methane (CH4), ammonia (NH3) etc.
R. Claudi (Sat,) studied this question.