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NASA Finds Us Our Very Own Tatooine 200 Light-Years Away

NASA's Kepler Space Telescope is finding out that some science fiction is reality.

NASA has found a real-life Tatooine. Sort of. The agency's Kepler telescope, that amazing deep field observatory out in space, found something awesome last week: two planets, Kepler 47-b and 47-c, orbiting a binary star. And what's more is that Kepler 47-c is in the system's habitable zone.

Tatooine's famous double sunset, the one Luke Skywalker watches with angst from his aunt and uncle's house, means the planet orbits a binary star. Binary stars are double star systems, two stars that orbit their common centre of gravity. This is usually a point in space between them called a barycenter. Pluto and its largest moon Charon have the same arrangement; they orbit a barycenter near Pluto but outside of both bodies.

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Binaries aren't rare. About half the stars in the galaxy are binaries, and they come in all different shapes and sizes. Their orbital periods vary, some stars make the circuit around their partners in a matter of hours while others take years. Kepler 47-b and 47-c orbit, fittingly, in the Kepler-47 system. This system's two stars eclipse each other every 7.5 days as seen from Earth. One star is similar to the sun in size and only 84 percent as bright, while the second star is diminutive, measuring just one-third the size of the sun and with less than 1 percent of its brightness. The system is about 4,900 light-years away in the constellation Cygnus.

via NASA

Finding planets around binaries a little less common, though not unheard of. Kepler 47-b and 47-c join just three other extrasolar planets scientists have confirmed to be orbiting binary stars: Kepler 16b, 34b, and 35b. That these planets exist at all is somewhat remarkable since they have to deal with a whole different set of circumstances compared to a planet that orbits a single star.

At first glance, it seems almost impossible that planets could form around a double star. It's not hard to imagine how the gravitational forces of two stars could keep any protoplanetary material from coalescing into a solid body. But, as with so many discoveries in space, scientists have to rethink their models to account for what they find rather than trying to fit the unexpected into some preexisting idea. One theory that's emerged about planetary formation around a binary is that planets in these systems form very far away from the stars in a gas clouds. It's the natural viscosity of the gas that keeps planetary fragments together until they become self-sustaining spheres. The phenomenon is known as as “gas drag.” These faraway planets gradually fall towards their double star over millions of years, eventually achieving a stable orbit far closer than they could have formed.

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Scientists found that Kepler 16-b stabilized pretty close to its binary, but not close enough for liquid water to exists on the surface. Kepler 47-b, one of the newly discovered planets, is on the other end of the spectrum. It orbits too close to its binary for life supporting liquid water to exist; it orbits the twin stars in less than 50 days. Such a short year has led scientists to imagine the planet is a sweltering world with a thick, superheated methane atmosphere — sort of like a methane version of Venus.

Kepler 47-c, the other new find, is in just the right orbit. It's in the habitable zone, or Goldilocks zone, that perfect orbit where liquid water could, theoretically, exist on the surface. Scientists figured this out from its year; the planet looks to be orbiting its stars every 303 days. On the down side, the planet doesn't seem to be terrestrial. Astronomer's think Kepler 47-c is a gas giant slightly larger than Neptune with an atmosphere of thick, bright water-vapor clouds.

So we might not have found a real Tatooine, but we're getting close. This latest find proves that planets can exist in the habitable zone of binaries. Now all we need to do is find one that's terrestrial, complete with laser-sword wielding farmboy.

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