The study of the universe—perhaps especially the study of life in the universe—often depends on a key assumption called the Copernican Principle. This principle, named after the Polish astronomer who proposed that Earth was not the center of the universe, posits that the same laws of nature hold true everywhere in the universe. Earth is not an exception to that rule; in other words, “we are nothing special.” This means that, if life formed on Earth because it had certain characteristics, then any other planet with those matching characteristics will have the same chance of eventually supporting life, too. The main question is, “Which characteristics are the important ones?” Scientists think that the keys to life on Earth are liquid water, the right chemicals, and a steady energy supply. It is not certain, though, that these are indeed the correct necessities for life, nor is it certain what kinds of life these conditions could support. What if life on Earth evolved along just one of many possible paths? Astronomers might not even recognize the life on these other planets!