The dim red star soon entered the collective imagination, inspiring dreams of interstellar travel. Gravity has linked the star to the Alpha Centauri system, but our culture of science and storytelling has linked it to the solar system. Today, that link will grow stronger, when an international team of astronomers announces that this nearest of stars also hosts the closest exoplanet, one that might look a whole lot like Earth.
No one will ever find a closer alien world than this. This is it. No other faint, cool stars lurk in the abyss between the Alpha Centauri system and our solar system. In a way, the first discovery of a possibly habitable planet in our backyard is also a final discovery. In the hunt for our cosmic neighbors, this planet is as good as it gets.
For now, the planet is unceremoniously called Proxima Centauri b. It zips around its namesake star every 11.2 days, and is likely locked in place—like the moon, which always shows the same face to Earth. It’s at least 1.3 times as massive as our planet, and based on its likely size, astronomers think it is rocky. Its home star is only .15 percent as bright as the sun, so the planet isn’t as scorched as you might expect, given its tight orbit. Instead, it circles around in a sweet spot that might allow for liquid water on its surface. “It’s in about the same position in the habitable zone of Proxima as the Earth is in the habitable zone around the sun,” says James Kasting, an astronomer at Penn State who was not involved in the new finding.
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