Using techniques of exquisite sensitivity and technological finesse, astronomers have spent the past two decades on an astonishing voyage of cosmic discovery. They have found that the universe is full of planets: cold, small, and dark next to their large and glaring suns, these worlds have previously been hidden from us. To spot them represents a challenge that has been compared to looking across thousands of miles to see a firefly buzzing around a brilliant searchlight. They exert a gravitational pull, tugging their parent stars into a gently wobbling motion that we can now detect. We now have firm evidence for thousands of planets, around thousands of stars. We also know something about these worlds, their sizes, their orbits, often their ages. In a handful of cases ... we have even measured the temperature of their upper atmospheres and [determined] their gaseous chemistry, finding substances like sodium, methane and water. 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.