It was a fanciful, charming idea by the filmmaker George Lucas, and it now turns out the real thing -- or something very much like it -- might actually exist. Scientists report today they have found a planet circling two stars, about 200 light-years away from Earth. Because every sun is a star, you might well see a double sunset from that planet.
Of the 1,600 so-called exoplanets so far discovered orbiting other stars, this is the first in a nice, stable, circular orbit around a binary star system.
"The 'Star Wars' link is striking," said Alan Boss of the Carnegie Institution for Science, who was a co-author of the study in Friday's edition of the journal Science. "The colors of the stars are a bit different from what Lucas showed, but if you could stand on that planet, you would see something pretty close to that."
The discovery was made using instruments on NASA's Kepler spacecraft, a telescope launched in 2009 to search for planets orbiting distant stars. The newly found planet, known as Kepler-16b, was much too far away to be seen directly, but the instruments were sensitive enough to detect a tiny dimming of the two stars, once every 229 Earth days, as that faraway planet passed in front of them and blocked a little of their light.
"This mission has been a lot of fun because we're discovering all sorts of stuff like this," said Nick Gautier, the Kepler project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Boss said, "This is just unqualified good stuff."
Kepler-16b was something of a surprise to space scientists. Many stars in the night sky are, indeed, double stars, but researchers had long debated whether they could even have planets. Gravity from the two suns would whipsaw planets in different directions, some argued, pulling them apart before they could even form.
What would it be like on Kepler-16b if we could go there? Not pleasant, Boss said. Even if they can't see it, they can calculate its size and its distance from the two stars at the center of its solar system. The planet, about as massive as Saturn, is probably a gas giant like Saturn or Jupiter, which means it probably does not have a solid surface on which one could stand. And the two stars, which circle close together, are both smaller and dimmer than our sun.
So it would be cold there -- "like a cold winter day in Antarctica," Boss said. "Not very nice."
But there might be other planets in the Kepler-16 solar system, perhaps close enough to those twin suns to have liquid water. Sensitive as the Kepler probe's instruments are, they have a tough time detecting planets the size of Earth.
"One would only need a smaller planet, a little closer, for this system to have been a real Tatooine," said Laurance Doyle of the SETI Institute in California.
He was the lead author of the paper in Science, and has long been researching the possibility of solar systems around double stars.
Boss raised the possilbility that Kepler-16b, the planet just found, has moons like Jupiter's -- and if, like some of Jupiter's moons, they have heat welling up from inside, they could be friendly to living things. Boss emphasized that this was pure conjecture, but then, nobody fully believed until now that a world with two suns could be anything more than the stuff of science fiction.
"We invited Lucas to the press conference," Boss said, chuckling.