The circumbinary planet Kepler-16b – the first planet known to definitively orbit two stars. The cold planet, with its gaseous surface, is not thought to be habitable. The largest of the two stars, a K dwarf, is about 69 percent the mass of our sun, and the smallest, a red dwarf, is about 20 percent the sun's mass. These star pairs are called eclipsing binaries. (Photo by T. Pyle/Reuters/NASA/JPL-Caltech)
