Imagined Life

Starred review from April 15, 2019
Posing a far-reaching question—what will alien life look like when humankind finds it?—the coauthors of Exoplanets explore possible answers in this lively, imaginative, and accessible look at cutting-edge exobiology. The first step for physicist/science writer Trefil, and Summers, a member of NASA’s New Horizon mission, is deciding how to define life. The basic definitions are broad, selected to cover every possibility imaginable so far. Next, the authors explore the clues, or “biomarkers,” that hint that a planet does—or did—harbor life. With those basics down, the book ranges widely, exploring an exotic variety of hypothetical life that might evolve on everything from Earthlike “Goldilocks” worlds with some surface water, to stormy, entirely water-covered worlds or dark “rogue” planets adrift in space with no home star. The discussion closes with a look at some really alien possibilities—life evolving in methane or ammonia instead of water, or inorganic life based on metals instead of carbon. Throughout, the spirited, nontechnical discussion is detailed enough to fascinate nonspecialist readers without overwhelming them. This is a marvelous introduction to a field fueled by both imagination and science.