This diagram compares our own solar system to Kepler-47, a double-star system containing two planets, one orbiting in the so-called "habitable zone." This is the sweet spot in a planetary system where liquid water might exist on the surface of a planet.
<p>Unlike our own solar system, Kepler-47 is home to two stars. One star is similar to the sun in size, but only 84 percent as bright. The second star is diminutive, measuring only one-third the size of the sun and less than one percent as bright. As the stars are smaller than our sun, the systems habitable zone is closer in.
</p><p>The habitable zone of the system is ring-shaped, centered on the larger star. As the primary star orbits the center of mass of the two stars every 7.5 days, the ring of the habitable zone moves around.
</p><p>This artist's rendering shows the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. One year, or orbit, on Kepler-47c is 303 days. While not a world hospitable for life, Kepler-47c is thought to be a gaseous giant, slightly larger than Neptune, where an atmosphere of thick bright water-vapor clouds might exist.
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For more, visit: <a rel="nofollow" class="external free" href="http://www.nasa.gov/mission_pages/kepler/news/kepler-47.html">http://www.nasa.gov/mission_pages/kepler/news/kepler-47.html</a>
NASA/JPL-Caltech/T. Pyle
<a rel="nofollow" class="external text" href="http://www.nasa.gov/mission_pages/kepler/multimedia/images/orbiting-in-habitable-zone-of-two-suns.html">Orbiting in the Habitable Zone of Two Suns</a>