John S. Lewis
-- What is the best world for life? A world on which the world and its life have co-evolved, accommodating each other. What is the best of all possible worlds? One that has been altered to our needs, and that we have met halfway by adapting ourselves. The best marriage of world and resident is consensual: both freely change for the common good. This is the direction in which we are already headed. It is best to be aware of it.
What kinds of planets, then, of all possible worlds, are well suited for eventual human occupation? A wide range indeed. There is a whole universe of opportunities out there, waiting for us; Earths and Earthlets, Earthissimos and Europas, terraformed non-Earths, planets of brown dwarfs and ocean satellites of Jovian planets around F, G, K, and M stars in spiral galaxies, globular clusters, and elliptical galaxies, and around orphan brown dwarfs in interstellar space; worlds of types known and unknown; worlds without end.
What kind of world do you want your grandchildren to live in?