Sometimes the corny wisdom that you can search far and wide for what’s right in front of you all along turns out to be true. For astronomers studying extrasolar planets—those around other stars, of which more than 3,500 are now known—the holy grail is an Earth-like world: small, rocky, and about the right distance from its star for liquid water to exist on the surface.
Now they have found one as near as could be. True, it is still a little more than four light years away—that’s around 25 trillion miles—but it is orbiting our Sun’s nearest neighbouring star, Proxima Centauri, in the constellation of Centaurus.
For one thing, the discovery drives home the message now abundantly clear from studies of extrasolar planets: terrestrial-like planets must be pretty commonplace throughout the cosmos. It’s now believed, on the basis of planet surveys to date, that around one in every five Sun-like stars has a planet of similar size and composition to Earth within their so-called habitable zone, where the temperature is right for liquid water to exist.