In 1750, British astronomer Thomas Wright published a book An Original Theory or New Hypothesis of the Universe with a diagram showing the stars of our Milky Way, each surrounded by orbiting planets.
But there was no evidence to support his view. "At that point in history," Samuel Arbesman writes in his book The Half-Life of Facts, "this notion was nothing more than a hope, and a somewhat sacrilegious one at that. It was no more than a logical deduction derived from the Copernican notion that our place in the universe need not be a particularly privileged one."
For more than 200 years, the idea that there were planets beyond our bubble (known as exoplanets) remained conjecture. As recently as 1980, the documentary Cosmos showed Carl Sagan speaking to a classroom full of children explaining how we might someday detect exoplanets' orbits. "By the time that you people are as old as I am," he says, "we should know for all the nearest stars whether they have planets going around them or not. We might know dozens or even hundreds of other planetary systems."
"That will happen in your lifetime," he continues, "and it'll be the first time in the history of the world that anybody found out, really, if there are planets around the other stars." No surprise, he was right. In 1995 astronomers found a planet orbiting a sun-like star, Pegasi 51, the first star-orbiting planet confirmed beyond our system. "Humanity," Arbesman writes, "in the course of a single issue of Nature, overhauled its view of the universe."
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