From ‘Star Wars’ to reality: Astronomers discover Tatooine world with two suns

September 15, 2011

In 1977, filmmaker George Lucas imagined what astronomers have now discovered: A planet with twin suns.

In one of the most iconic images in “Star Wars,” hero Luke Skywalker broods as double suns set on the desert world Tatooine.

Anyone on the newly found planet Kepler 16B would enjoy a similar stunning sight.

“It’d be a weird cocktail hour,” said astronomer Alan Boss of the Carnegie Institution of Washington, a member of the discovery team. “The sun would go down and you’d have a drink and then, a few hours later, the other sun would go down while you have another drink.”

The double-barreled sunrises, he added, would “wreak havoc with the roosters.”


An artist's impression of the newly-discovered planet Kepler 16b, which, like the planet Tatooine in the movie Star Wars, orbits twin suns. (NASA/JPL-Caltech)

Unlike Tatooine, though, Kepler 16B is unlikely to host any heroes. Roughly the size of Saturn, the planet has no real surface and, instead, seems to be made of an icy, rocky core surrounded by hydrogen and helium gas. The planet is too cold for liquid water, with an average surface temperature about 100 degrees below that of Earth’s.

Any alien Luke Skywalkers would need to be brooding on one of the planet’s moons, which, while they have not been detected, likely exist, Boss said. On such a moon, “Luke would be wearing an Eskimo parka and walking across an icy field like in Antarctica.”

Astronomers have caught hints of planets circling double stars before, but Kepler 16B marks the first solid detection of such a world — one locked in a dramatic dance with its suns.

The two stars, about 200 light years from Earth in the constellation Cygnus, circle each other every 41 days. One star is small, red and dim, throwing off just 20 percent of the light of our sun. The other star, bigger and orange, generates about 70 percent of the light of our sun.

Kepler 16B circles them both, taking 229 days to complete an orbit. As it does, it passes in front of each star, blocking a small fraction of their light.

NASA’s Kepler space telescope detected these dips in brightness. In fact, Kepler saw four such winks, a sequence that could mean only one thing.

“You see two stars going in front of each other, and you see the planet going in front of both of them,” Boss said. “So you see four dips in luminosity. Seeing those, you can prove there’s no other explanation than a third object moving in front of both stars.” That object, further calculations showed, was a planet roughly the size and mass of Saturn.

As the two stars twirl about each other, they would appear to grow closer and further apart in the sky of Kepler 16B. About every 20 days, the twin suns would rise and set together. In between, the two stars would appear to drift apart.

Astronomers say double, or binary, stars are as common in our galaxy as solitary stars like our sun.

A team led by Laurance Doyle of the SETI Institute in Mountain View, Calif., describe the discovery in the journal Science.

“Nobody has ever seen a place like this before,” said Doyle at a news conference.

With one exception: a sad moment early in “Star Wars” when Skywalker watches two suns setting. When Lucas came up with the idea, he merely wanted audiences to know that Tatooine was an alien planet far from Earth, said John Knoll, visual effects supervisor on three of the six “Star Wars” films.

Kepler 16B shows such planets could be common in the galaxy, said astrophysicist Greg Laughlin of the University of California at Santa Cruz, who was not involved in the work. He called the Kepler 16 system a laboratory for revising theories of planet formation.

The discovery adds to the huge haul of planets Kepler has caught glimpses of since the $600 million mission launched in 2009. This week at the Extreme Solar Systems II meeting in Wyoming, Kepler astronomers said the telescope has found 1,781 “candidate” planets among some 155,000 stars it’s studying.

And on Monday, astronomers using a telescope in Chile announced finding a rocky planet not much larger than Earth at the edge of its star’s “habitable zone,” meaning it could potentially host liquid water — the main ingredient for life as we know it.

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