Free Astronomy Magazine September-October 2014

ASTROBIOLOGY telligent life on Earth just a century ago, would have concluded that there was none. So why, then, look for those substances in alien atmospheres? Would it not be suffi- cient to search for less exotic biomarkers? After all, a relatively high concentration of, for example, molecular oxygen (O 2 ), ozone (O 3 ) and methane (CH 4 ) may already be in- dicators of the presence of some form of life on the surface, also because oxygen and methane tend to coexist only if con- tinuously supplied by biological activity. If in addition there is also a non-negligible presence of nitrous oxide (N 2 O –typ- ical gaseous pollutant co- responsible for the green- house effect) it is even possible to assume the existence of an industrial civilization. Not necessar- ily though. In fact, even if those molecules were to be found in great abun- dance they could be of non-biological origin, so much so that even in the Earth’s atmosphere there is a high and con- stant contribution of those molecules which is not associated to anything living. Hence the need to look for something that the environment cannot create by itself in significant amounts and, perhaps most im- portantly, that the search for that some- thing be conducted as a sideline activity to less tentative investigations, as it would be unthinkable to have exclusive use (even for short periods) of a state-of-the-art tele- scope for a search whose outcome is some- C omparison between the size of a white dwarf with that of the Earth. They are practically identical, which means that the maximum possi- ble contrast be- tween the lines of the planetary spectrum and the stellar background will be had dur- ing the transit of the planet on the star (actually an eclipse). [ESA/NASA] In the side video, a suggestive pre- view of the JWST mission. [NASA]