  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 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-/ground-based instrumentation. Space missions, such as JWST and the very
recently proposed ARIEL (ESA M-Class Mission), or ground based instruments
(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. Most of exoplanets have local counterparts in the Solar
System planets that are available for comparative studies, but there are also
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 the
knowledge of planet atmospheres, main objective of future exoplanetary space
explorations. 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, carbon monoxide, methane, ammonia etc.
