David Grinspoon is the author of “Lonely Planets: The Natural Philosophy of Alien Life.” He tells Anne Strainchamps we’re more likely to find microbes, but can’t help longing to find other creatures to talk to, and that if and when we do, such a find will pose a big challenge to traditional religions. Does every life form rank its own Redeemer, or is Jesus Christ, as some have maintained, a planet-hopper?