It's been almost a year ago since we made our first discovery of an exoplanet orbiting two suns, prompting everyone to compare it to the planet Tattooine in the "Star Wars" universe. A handful of other planets orbiting two stars have been found since then, but the Kepler-47 system is special: It's the first twin star system discovered that has not one but two planets in orbit.
This unusual system was discovered using data from the Kepler telescope that's responsible for numerous exoplanet finds. According to Kepler mission principal investigator William Borucki, "Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been — do they have planets and planetary systems? This Kepler discovery proves that they do."
The first star in the system is comparable to our sun in size, although only 84% as bright. The other is a dim star, measuring a third of the sun's size and only 1% as bright. Kepler-47b, one of the two planets that most probably has a blazing hot atmosphere due to its proximity to the stars, completes its orbit within 50 days. With a radius three times larger than Earth's, it's currently the smallest planet known to orbit two stars.
The other planet, called Kepler-47c, is located much farther away and completes its orbit around the stars in 303 days. But even though it's located in the system's habitable zone, it's unlikely to support life — the planet is a gas giant that's slightly larger than Neptune.
Kepler-47's discovery means exoplanet hunters now have to pay special attention to clusters of stars that may be hiding more than one planet. As Borucki said: "In our search for habitable planets, we have found more opportunities for life to exist."
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