We might find life in our own neighborhood: beneath the Martian surface, perhaps, or in the dark, subsurface oceans of Jupiter's moon, Europa. Or maybe the dream of the ages will come true, and we'll eavesdrop on the communications of extraterrestrial civilizations. We might even capture evidence of "technosignatures," or traces of technology (think smog). Barring these strokes of luck, however, the job will be much harder. Light will be the key – light from the atmospheres of exoplanets, split up into a rainbow spectrum that we can read like a bar code. This method, called transit spectroscopy, would provide a menu of gases and chemicals in the skies of these worlds, including those linked to life.
An enormous body of science is being assembled to analyze and explain the origins, characteristics and possible extraterrestrial dimensions of life. By exploring and illuminating the world of extreme life on Earth, by experimenting with how life here began, and by understanding more about the chemical makeup of the cosmos, we move closer to an answer to the question, ‘‘Are we alone?’’