Alone in the Universe: Why Our Planet Is Unique

“The Milky Way contains a few hundred billion stars, but almost certainly contains only one intelligent civilization,” says astrophysicist and veteran popular science writer Gribbin (The Theory of Everything). In an infinite universe, on the other hand, anything is possible, but we can only explore such questions closer to home. Gribbin makes a thoroughly lucid and convincing case. Recent astronomical observations have shown that exoplanets—worlds orbiting other stars—are more common than we expected, but Earth-like worlds are rare. And even planets in a “habitable zone” of both a galaxy and an individual star need water and the right organic compounds to engender and sustain carbon-based life. “Life got a grip on Earth with almost indecent haste,” but it took Earth’s metallic core and a near-twin Moon to stabilize Earth’s tilt and steer off dangerous radiation; equally advantageous to Earth, Jupiter’s mass pulls in most of the comets and asteroids that might otherwise smash into us. Gribbin lays out the details one by one, building a concise case that “[w]e are alone, and we had better get used to the idea.” (Dec.)