Extrasolar systems shed light on our own

Amazing as the discoveries of planets, comets, and asteroid belts around other stars are, it’s their potential to shed light on our Solar System’s origins that is exciting astronomers. A planet smaller than Mercury circles a star 210 light-years away. Around another star, two planets live so close together that each periodically rises in the other’s sky. Other alien skies are home to two suns that rise and set, casting double shadows over their double-sunned worlds. Planets so dense they might have diamond rinds, worlds whose year is shorter than an Earthday, others that orbit their star backward—the cosmos holds many exotic and diverse objects. And yet, among the eclectic oddities are a few planetary systems whose smaller residents look intriguingly familiar. By many standards, these systems are very much like home: In addition to multiple planets, some stars are ringed by belts of small rocky bodies, like our comets and asteroids. Now, astronomers can use the Solar System’s architecture to predict the presence of unseen objects in these systems, and use the systems to learn more about the celestial events that gave birth to and shaped our Solar System. “We definitely learn more about the Solar System’s past and future by observing other stellar systems,” says astronomer Kate Su of the University of Arizona, Tucson, AZ. “Our challenge now is to identify common features and link them to what we know about our own Solar System,” she says. These common features are moving Earth—and the Solar System—even further from the realm of the unique, and advancing an almost inexorable Copernican march toward the surprisingly mundane. “In a broader sense, we’re trying to understand if our own world—and our own Solar System—is ‘normal,’” says David Grinspoon, Chair of Astrobiology at the US Library of Congress in Washington, DC, “or, in …