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Alpha Centauri Has a Planet

A newly discovered planet circling Alpha Centauri is only four light years away and could point the way to habitable planets nearby

This is the Lambda Centauri nebula, a star-forming cloud in our Milky Way galaxy, also known as the Running Chicken nebula. Image: NASA

Alpha Centauri is the brightest star in the constellation Centaurus. It was the star at the center of the Tranformers’ universe, the destination of the Lost in Space crew and the sun of James Cameron’s Avatar. It’s only four light years away, and now, it has a planet. Yes, the planet is probably uninhabitable. But it might lead the way to habitable planets nearby. Be still our hearts.

The BBC reports:

The planet has at minimum the same mass as Earth, but circles its star far closer than Mercury orbits our Sun.

It is therefore outside the “habitable zone” denoting the possibility of life, as the researchers report in Nature.

For a more poetic take, there’s Centauri Dreams:

Anyone in the Southern Hemisphere can look up on a clear night and easily see Alpha Centauri — to the naked eye, the three suns merge into one of the brightest stars in Earth’s sky, a single golden point piercing the foot of the constellation Centaurus, a few degrees away from the Southern Cross. In galactic terms, the new planet we’ve found there is so very near our own that its night sky shares most of Earth’s constellations. From the planet’s broiling surface, one could see familiar sights such as the Big Dipper and Orion the Hunter, looking just as they do to our eyes here. One of the few major differences would be in the constellation Cassiopeia, which from Earth appears as a 5-starred “W” in the northern sky. Looking out from Alpha Centauri B b and any other planets in that system, Cassiopeia would gain a sixth star, six times brighter than the other five, becoming not a W but a sinuous snake or a winding river. Cassiopeia’s sixth bright point of light would be our Sun and its entire planetary system.

This is a big deal. The BBC again:

“Alpha Centauri B is of course a very special case – it’s our next door neighbour,” said Stephane Udry of the Observatory in Geneva and senior author of the paper.

“So even if the discovery just stands perfectly normally in the discoveries we have had up to now, it’s a landmark discovery, because it’s very low-mass and it’s our closest neighbour.”

Now, this Earth-like planet is only really vaguely Earth-like. New Scientist explains:

The team calculates that the new planet is 1.13 times the mass of Earth, which means it is likely to have a rocky composition. However, with a “year” of just over three Earth days, this rocky body is not our planet’s twin.

“The surface temperature must be hundreds – thousands – of degrees. There is perhaps lava floating on the planet,” says Dumusque. Still, planets tend not to be loners, so the Alpha Centauri system should have more. There’s a chance these undetected worlds are in the habitable zone, the region around a star most likely to support life as we know it.

Okay so what if we try to go there? Wired describes it this way:

So what would it look like if we sent a rocket to Alpha Centauri? The triple star system is made up of two sun-like stars, Alpha Centauri A and Alpha Centauri B, as well as the dwarf star Alpha Centauri C. Compared to our sun, Alpha Centauri A is slightly larger and brighter while Alpha Centauri B is just a little smaller and half as bright.

Days on a planet orbiting Alpha Centauri A or B would follow a weird alien cycle. When the surface pointed toward the parent star, it would have daytime much like our own and when it turned away from both stars it would experience an Earth-like nighttime. But when the planet was between the two stars, it would have a third option: a twilight-like evening lit by a bright star. Everything would appear as if outside a floodlit stadium at night.

Only time will tell whether or not this new planet is as promising as we all want it to be.

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About Rose Eveleth
Rose Eveleth

Rose Eveleth is a writer for Smart News and a producer/designer/ science writer/ animator based in Brooklyn. Her work has appeared in the New York Times, Scientific American, Story Collider, TED-Ed and OnEarth.

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