Science fiction has turned into reality': Astronomers hail extraordinary discovery of 'Star Wars' planet with two suns

It is one of the most memorable images from Star Wars, Luke Skywalker gazing into the distance while walking on Tatooine, a planet with two suns.

And more than three decades after the movies came out the real life version has been discovered - a freezing cold planet named Kepler-16b, which is about the size of Saturn and 200 light years away.

American researchers using observations from NASA's Kepler spacecraft detected the distant planet, which is treated to a double sunset every evening.
'This discovery is stunning,' Alan Boss of the Carnegie Institution for Science Department of Terrestrial Magnetism said.

'Once again, what used to be science fiction has turned into reality.'

Binary stars -- two suns turning around each other -- have been seen before, and astronomers have suspected planets exist around them, but Kepler's observations are the first to confirm it.
The gravitational pull of two stars, even stars like the relatively small ones at the heart of this stellar system, would be quite different from the gravity exerted by just one star, Mr Boss said.

Kepler's mission is to scour our section of the Milky Way galaxy for Earth-like planets in the so-called 'habitable zone' that is not too close and not too far away from the stars they orbit.

The spacecraft does this by finding stars whose light periodically gets dimmer, which means there is a planet passing between the star and Kepler's instruments. This is known as a planetary transit.
What made this find so eye-popping was that the stars were eclipsing each other as first one and then the other got in the way. And then a third eclipse indicated a planet was part of the system.

If the notion of a planet with two suns was displayed in the earliest Star Wars film on the fictional planet Tatooine, home of Luke Skywalker.

Tatooine was a rocky, desert planet, but Kepler-16b is a cool gas giant, Boss and other researchers said.

Because both of its suns are smaller and cooler than our sun, Kepler-16b would be quite cold, with a surface temperature of around minus 100 to minus 150F (minus 73 to minus 101C).
Kepler-16b is similar to Saturn in size and mass, a cold gas giant that orbits its two suns every 229 days at a distance of 65 million miles (104.6 million km).

That is roughly the same distance as Venus's orbit, compared to Earth's 365-day orbit around the sun at a distance of about 93 million miles (149.7 million km).

The newly detected planet is 200 light-years from Earth and is not thought to harbour life. A light-year is about six trillion miles (10 trillion km).

'Kepler-16b is the first confirmed, unambiguous example of a circumbinary planet - a planet orbiting not one, but two stars,' said co-author Josh Carter.

'Once again, we're finding that our solar system is only one example of the variety of planetary systems nature can create.'

Kepler-16b

Kepler-16b is an extra solar planet. It is a Saturn-mass planet consisting of half rock and half gas, and it orbits a binary star, Kepler-16, with a period of 229 days. This is the first observationally confirmed example of a circumbinary planet.

The planet was discovered using the space observatory aboard NASA's Kepler spacecraft. Scientists were able to detect the planet using the transit method, when they noticed the dimming of one of the system's stars even when the other was not eclipsing it. Furthermore, the transits made by the planet have allowed for an unusually high precision in the calculations of the sizes and masses of objects in the Kepler-16 system. The leader of the planet's discovery team, Laurance Doyle of the SETI Institute in Mountain View, California, said of this precision, "I believe this is the best-measured planet outside the solar system."

Kepler-16b is also unusual in that it falls inside the radius that was thought to be inner limit for planet formation in a binary star system. According to Sara Seager, a planetary expert at the Massachusetts Institute of Technology, it was thought that for a planet to have a stable orbit around such a system, it would need to be at least seven times as far from the stars as the stars are from each other. Kepler-16b's orbit is only about half that distance.

As seen from Earth, the planet will cease transiting one star as soon as 2014, and will stop crossing the second and brighter star in 2018. After that, the planet will remain undetectable using the transit method until around 2042.

Astronomers have informally referred to Kepler-16b as "Tatooine", after the fictional planet that is a key setting in the Star Wars film series; a scene in the first film depicts a double sunset on Tatooine.