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.

July 15, 2019
Are we alone in the universe? Two well-known astronomers tackle the possibilities in this tour of exoplanets. We know of only one planet on which life exists--Earth--but is life an everyday chemical and physical reaction in the universe or a unique fluke? We have a pretty good idea of some of the steps that led to life on Earth and a firm understanding of how it evolved since then. So how does this apply to the types of exoplanets we may encounter? Would life develop there as it did on Earth? How different could it be? Given the complexity and diversity of exoplanets we have found, will the answers be correspondingly complex and diverse? These are some of the questions approached by George Mason University physics and astronomy professors Trefil and Summers (co-authors: Exoplanets, 2018, etc.) in this sober yet enervating examination of possible life scenarios on a variety of exoplanet settings. First, the authors define life, which can be handled as a list (adaptation, growth, homeostasis, metabolism, organization, reproduction, responsiveness), a process (the NASA definition is "a self-sustaining chemical system capable of Darwinian evolution"), or in terms of thermodynamics. The authors then take these definitions and apply them to a variety of possible planets: one with a rocky mantle and a metallic core overlaid with ice; one with an ocean beneath ice; in another, a land-and-water combination, etc. They probe each scenario to imagine how life could have taken shape given the opportunities and constraints. Trefil and Summers try their best to keep the language geared to a lay audience, but they can't avoid some formulas: "Galileo's argument rests on the fact that the volume, and hence the mass, of a structure depends on the cube of its dimensions, while the size of the support area depends on the square." Overall, though, the prose is straightforward, and the authors make the potentialities of exoplanet life intriguingly real. Finally, they consider nonorganic life forms, for instance silicon chemistry replacing carbon-based life forms. A curiosity-whetting investigation of imagined life beyond our world.

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August 1, 2019

Following up Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets, and the New Search for Life Beyond Our Solar System, astronomers Trefil and Summers examine how the laws of chemistry and physics would shape the evolution of life and civilization on unusual worlds. Their survey includes an internally heated "snowball," a tidally locked windswept planet, and four (renamed) theoretical celestial bodies featured in their previous work. While cautioning that terrestrial biases might lead us to overlook unusual life forms, the authors openly indulge in "water chauvinism" (even though other liquids might substitute as biochemical solvents elsewhere in the universe) and "chemical chauvinism" (although it's possible that complex structures could evolve through purely electromagnetic processes). Exoplanets' carbon, stellar, and surface chauvinisms also reemerge. NASA's striking "Exoplanet Travel Bureau" graphics and amusing discussions by hidebound space alien academics, incredulous that anything could survive on planets different from theirs, offset a dull chapter enumerating already discovered extrasolar planets. This relatively easy read is an appealing addition to the growing body of recent works addressing the possibility of extraterrestrial life. VERDICT Both popular science and sf readers will enjoy this extrapolative natural history.--Nancy R. Curtis, Univ. of Maine Lib., Orono

Copyright 2019 Library Journal, LLC Used with permission.

August 1, 2019
Humanity's understanding of the universe has never been better, write physicist Trefil and astronomer Summers (Exoplanets, 2017), yet one of the oldest and most profound questions remains: Are we alone in the universe? The authors' attempt at an answer (or, more precisely, answers) takes form as a systematic and inventive exploration of the nature of life in distant and unknown worlds, informed by their guiding principle: If you can imagine a world that is consistent with the laws of physics, then there's a good chance that it exists somewhere in our galaxy. They consider the possibility of life like us (organic beings in imagined worlds based on actual discovered exoplanets), life not like us (formed by something other than carbon or water), and life really not like us (like artificial intelligence). As galactic tour guides, the authors demonstrate an infectious, playful curiosity alongside their technical prowess, maintaining a light touch with some heavy science. Will appeal to sf newcomers and budding space nerds.(Reprinted with permission of Booklist, copyright 2019, American Library Association.)