No matter how conservative or optimistic we are, the statistics tell us that something like an astonishing one out of every seven stars must harbor a planet similar in size to the Earth, and at roughly the right orbital distance to allow for the possibility of a temperate surface environment. In other words, roughly 15 percent of all suns could, in principle, be hosting a place suitable for life as we know it.
Since our galaxy contains at least 200 billion stars, this implies a vast arena for the universe’s ubiquitous carbon chemistry to play in — a process that, as here on Earth, might lead to the complex machinery of life. Indeed, there is a 95-percent confidence — give or take a few percent — that one of these worlds could be within a mere 16 light years of us. That’s a stone’s throw, practically our galactic backyard.