All These Worlds Are Yours

Starred review from September 12, 2016
In this energizing book, Willis, associate professor of astronomy at British Columbia's University of Victoria, charts how the 1977 "discovery of deep-sea hydrothermal vents on Earth has transformed our view of the habitability of the outer solar system" and bolstered the search for life elsewhere. Microbes dependent on the energy of otherworldly, belching hydrothermal vents on the deep ocean floor were hailed as the first evidence that life may exist in extremes of space. Since then, discoveries of potential parallel life formsâand parallel ecosystemsâhave snowballed. The liquid methane cycle of Saturn's moon Titan "mirrors the hydrological cycle on Earth," Willis writes, and resembles the conditions on "early Earth before life arose." An ocean on Jovian moon Europa resembles Antarctica's frozen Lake Vostok. Similarly, warm salty oceans on Jovian and Saturnian moons are not altogether different "from the warm salty water that constitutes the bulk of our cells and that we retain as a chemical memory of our origins." The Kepler space observatory, designed to detect Earth-like planets orbiting sun-like stars, has discovered more than 3,500 "candidate planets" by measuring the dimming light of suns as planets pass; one of those planets, Willis notes, could be sufficiently like ours to harbor life. Through humorous, concise, accessible writing, Willis eloquently presents the growingâthough still circumstantialâevidence that we are not alone.