Remember Tatooine, the desert planet that was home to Anakin and Luke Skywalker in "Star Wars"? The sky was forever decorated with two stars, as the planet was part of a binary star system. It turns out this isn't just a fantasy.

Previously, astronomers had no evidence that rocky, Earth-like planets could exist in binary systems. They only observed gas giants in such systems, and only one system that even had more than one planet. As a result, the search for habitable planets was confined to single star systems although binary systems make up about 50 percent of all stellar systems. So the search was incredibly limited -- until now.

Astronomers at Ohio State University led by Andrew Gould used a theoretical technique developed by Einstein to detect binary star systems and applied it to the study. They found a frozen, rocky planet twice the mass of Earth, orbiting one of the system's stars at about the same distance Earth orbits the sun. 

The discovery of this exoplanet, called OGLE-2013-BLG-0341LBb, almost doubles the frontier in which astronomers hope to find habitable planets.

The team used a process called gravitational microlensing, which senses distortions in the light signals from binary systems, and can detect gravitational effects exerted on the stars' lights by the planet in question.

"The effect is not obvious," said Gould. "You can't see it by eye, but the signal is unmistakable in the computer modeling." The astronomers first discovered the planet and its host star, and then, thanks to their careful and painstaking observations, they noticed the second star in the system.

According to Scott Gaudi, an astronomy professor at Ohio State University, gravitational microlensing can yield estimates of an exoplanet's mass and distance from a given star even without the distortion in the light signals. Prior to this study the method was just an idea. Now these researchers have empirical evidence of its success. They are still trying to understand exactly why the method works, but according to Gaudi "it's at the frontier of our theoretical work."

The binary system is about 3,000 light years away. Despite being massive and rocky, however, the Earth-like planet with its Earth-like orbit is too frozen (about -352 degrees Fahrenheit) to plausibly contain signs of life. The star it orbits is too small, too red, and a bit too cold to support life. But the study, which was published in the July 4 issue of Science, still proves that Earth-like planets can indeed exist in binary systems. 

The study was conducted with the Optical Gravitational Lensing Experiment telescope as well as observations made by a collaboration of amateur astronomers from around the world.

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