Say the word “terraforming” amidst a gathering of space enthusiasts and it’s a bit like upending your beer mug in an Australian pub. It means you’re ready to duke it out with anybody in the joint. And the fight usually breaks out along these lines: One team sees the quest to replicate the biosphere of Earth on other planets as a moral imperative, an inevitable destiny, or both. Others -- equally passionate -- recoil at such pretension, proclaiming with surety that humans have no right to interfere with Nature as writ large upon the face of other worlds. Both viewpoints...