Published online by Cambridge University Press: 24 September 2020
Here, I examine whether some of the exoplanets that we have already discovered might be inhabited. However, I start by cautioning against an overly optimistic stance. Although we now know of thousands of exoplanets, and although the Drake equation estimates of Chapter 12 suggest that millions of planets are inhabited, a quick calculation suggests that of the exoplanets discovered so far, only a few are likely to have microbial life and none to have animal life. Against that background, we look at four planetary systems that are reasonably promising. One of these is the Kepler-186 system, where planet f may be habitable. Another is the Alpha Centauri system, where Proxima b may be habitable. A third is TRAPPIST-1, where there are three potentially habitable planets. The final one is Kepler-452, where planet b may be habitable. Whether any of these planets are actually inhabited will only be answered by particular kinds of observation – most likely spectroscopic studies of their atmospheres. How realistic such studies are depends on the distance to the system concerned. The four systems used as examples here range from 4 to nearly 2000 light years – from doable to quasi-impossible.