"Kepler-47 shows us that binary stars can have close-in planetary systems, just like the ones we see in single stars," study lead author Jerome Orosz at San Diego State University told SPACE.com. "Most of the stars in the galaxy are in binary or higher-order multiple systems, so the fact that planetary systems can exist in these types of systems is important. If we were restricted to looking for planets around single stars, we would be missing most of the stars in the galaxy."
The planets are much too far away to see with the naked eye. Rather, they were discovered by the drop in brightness they cause when they cross in front of, or transit, their host stars.
This dimming is tiny, only 0.08 percent for planet Kepler-47b and 0.2 percent for planet Kepler-47c. By comparison, Venus blocked about 0.1 percent of the sun's surface during its recent transit. Data from Kepler enabled researchers to deduce the relative sizes of the objects and orbits. They also relied on follow-up observations performed by telescopes at the McDonald Observatory in West Texas.
One of the stars is much like our sun, and the other is about a third its size and 175 times fainter. The inner and outer planets are respectively 3 and 4.6 times Earth's diameter — the smaller planet is the smallest circumbinary planet seen yet. [Tatooine-Like System Found, 2 Planets, 2 Stars (Video)]
The inner world completes an orbit every 49.5 days, while the outer one takes 303.2 days, giving it the largest known orbit for any transiting exoplanet. The stars themselves whirl around each other every 7.5 days.