IMAGINED LIFE

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.