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"  NASA&amp;#039;s planet-hunting Kepler Space Telescope has found two more planets that each orbit dual stars. The discovery, the work of a team led by William Welsh of San Diego State University, leads scientists to believe that alien worlds where two suns burn in the sky are far more common than once thought. And it just so happens that many of these planets may be in their solar systems&amp;#039; habitable zones. Back in September, a group of astronomers evoked visions of Luke Skywalker gazing across the horizon at twin suns when it announced the discovery of a planet, now known as Kepler-16b, orbiting dual stars. But at the time, astronomers didn&amp;#039;t know if the planet was anything more than an anomaly. &amp;quot;The universe is full of one-hit wonders,&amp;quot; Welsh says.  The new planets, called Kepler-34b and Kepler-35b, are both located in the constellation Cygnus. They&amp;#039;re among the most distant planets ever discovered, at 4900 and 5400 light-years away, respectively. And their existence establishes planets orbiting two stars as a new class of planetary system. In fact, according to the University of Arkansas&amp;#039; Claud Lacey, an expert in binary star systems who was not involved in the new study, it shows that &amp;quot;they probably are pretty common.&amp;quot; That came as a surprise to some astronomers. Besides the fact that no one had ever detected a two-star planet until last year, Welsh says, the physics at work in the tumultuous environment around a binary star system doesn&amp;#039;t seem friendly to planet formation. Because the stars are orbiting each other, the gravity in such a system is constantly changing, and that in turn changes the forces acting on any objects within the system. It&amp;#039;s hard to picture molecules coalescing into planets in such an environment, Welsh says. &amp;quot;It just isn&amp;#039;t a gentle place.&amp;quot; It&amp;#039;s possible that Kepler-34b and -35b formed farther out in their systems, where conditions would have been more stable, and migrated inward to their current orbits, Welsh says. Or, perhaps, it&amp;#039;s simply not so difficult to form a planet as scientists once thought. &amp;quot;If you can have planets in an environment that is this chaotic, then nature must like making planets,&amp;quot; Welsh says.  The locations of the three two-star planets discovered so far are particularly interesting for another reason. All three are right on the edge of being in the habitable zone\u2014the just-right distance from their parent stars that would allow them to have liquid water. Kepler-16 is a bit too cold, Welsh says, and Kepler-34b and -35b are a bit too warm, but all lie remarkably close to the sweet spot.  Welsh doesn&amp;#039;t think that this is just a coincidence. It may be, he says, that the distance these planets need to be from their stars to be stable, solid planets just so happens to be the same distance required to place them close to the habitable zone. If he&amp;#039;s right, then two-star systems could be a good place to look for earth-like planets\u2014systems with two stars are actually more common than our own single-star setup. Kepler-34b and -35b aren&amp;#039;t likely to harbor life themselves. They&amp;#039;re gas giants nearly the size of Jupiter, probably without much rock in their interiors. If something did live there, it would have to be a very strange creature indeed. &amp;quot;One can conceive of some sort of organism developing in the atmosphere of a gas planet,&amp;quot; Lacey says. &amp;quot;Perhaps a large, floating-type animal that could adjust its density so that it could rise and fall in the atmosphere.&amp;quot; The Kepler telescope, which astronomers used to find all three two-star planets, continuously watches 160,000 stars, searching for earth-like planets. Its mission is due to end this fall, but astronomers like Welsh think that if NASA extends the telescope&amp;#039;s time in space, it could make many more discoveries like this one. &amp;quot;[It&amp;#039;s] really revolutionizing the study of stars,&amp;quot; Welsh says. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/space/deep-space/a7346/is-the-universe-riddled-with-tatooine-planets-6638836/>