The Tatooine-like world about the size of Saturn is a frozen mass of rock and gas about 200 light years from Earth. NASA astronomers say it was discovered by the Kepler spacecraft launched in 2009.The desert planet of Tatooine is home to all manner of wonderful creatures — womp rats and banthas and jawas. But any proper "Star Wars" fan knows that the planet's most dynamic feature is its two suns, creating a magnificent double sunset that a young Luke Skywalker stares into during his wistful moments.
On Thursday, astronomers announced the discovery of a real planet that orbits two suns, a scenario that breaks so many galactic rules that it was thought by many to exist only in science fiction.
The planet, called Kepler-16b, is about 200 light years from Earth and is believed to be a frozen world of rock and gas, about the size of Saturn. It orbits two stars that are also circling each other, one about two-thirds the size of our sun, the other about a fifth the size of our sun. Each orbit takes 229 days; the stars eclipse each other every three weeks or so.
Scientists made the finding through NASA's Kepler spacecraft, which launched in 2009 and has been a driving force in the recent explosion in the discovery of distant planets.
The effort is a building block in the search for life; the next step is to determine which of those planets are Earth-like "candidates" for harboring life — too big and they're made of gas; too small and they won't have enough of an atmosphere.
Kepler monitors tens of thousands of stars, and it was during its survey of unexplored pockets of the galaxy that it detected the two stars eclipsing each other.
Astronomers then found that the brightness of the system dipped again when the stars were not eclipsing each other — the first evidence of a third body.
Further study showed that the third body popped up time and again as it circled both stars in what is known as a circumbinary orbit.
The team of astronomers, based out of NASA's Ames Research Center in Mountain View, southeast of Palo Alto, then calculated the mass of the third body by measuring the time sequence of the eclipses, which provided a roundabout look at the stars' gravitational strength.
The planet is so cold that it is not thought to harbor life. However, scientists expect the discovery to dramatically alter the search for planets because roughly half the distant stars that are being studied are part of "double star" systems, and many believed those systems to be so disjointed and volatile that they could never sustain a planet.
"Here's a live one," said Nick Gautier, a Kepler project scientist at the Jet Propulsion Laboratory in La Cañada Flintridge. "This tells us that you can have planets in the habitable zones around binary stars — which doubles the potential real estate that we ought to be thinking about for habitary planets in the galaxy."
Scientists have been searching for a planet orbiting two stars for decades. Periodically, a research group claims to have found one"but people were not really convinced," said Avi Shporer, a UC Santa Barbara astrophysicist and a member of the Kepler team.
"You cannot argue with this kind of evidence," he said. "This system is like a laboratory to learn about planets and stars. We didn't really know whether a planet could actually evolve in such an unstable environment. Now we know that it can."
The Kepler spacecraft, Shporer said, will continue expanding its search.
"Maybe there is some Luke Skywalker out there looking at a double sunset," he said. "It's a big extrapolation — but this is the goal. I think that the best discoveries — the most exciting ones — are still awaiting us."