It may be the biggest question in science: does life exist elsewhere in the universe?
For those who hope the answer is “yes”, the recent harvest of exoplanets by NASA’s Kepler Space Telescope has been hugely encouraging. As of early 2015, in the small slice of sky under its exacting gaze, Kepler has found at least a thousand extrasolar planets, a handful of which might be rocky Earth-sized planets in the so-called ‘habitable’ zone where liquid surface water may exist. Extrapolating Kepler’s results, astronomers estimate our Milky Way galaxy alone might hold some 10 billion Earth-like planets. With that much real estate, complex or even intelligent life must have formed on at least some of these planets, right?
Well, maybe not. In a sobering paper published late in 2014 in the prestigious Physical Review Letters, astrophysicists Tsvi Piran and Raul Jimenez argue that most planets in the universe have been wracked by frequent galactic-scale environmental catastrophes that could destroy nascent life more complex than a single-celled organism.