With the discovery of more and more exo-planets, we learn how common planatery systems seem to be in this galaxy and, by extension, the Universe. We don't need the Drake equation to imagine the possibilities. > One cannot extrapolate from an example of one but the insights into how life developed here appear to show that the Universe is poised to produce life whenever the conditions are right. - So far the planets discovered have not matched our home. And how difficult that match can be is shown in the book "Rare Earth",2000, by two very real scientists: Peter Ward and Donald Brownlee. I suggest reviewing it.