The vast majority of stars in the Milky Way don’t go it alone — most have a companion, or even two or three. It stands to reason that life outside the solar system might have a sky less like our own and more like Tatooine, the Star Wars planet with a double sunset.
Many binary systems host exoplanets, but astronomers still don’t have a good understanding of how planets could form in stable orbits around multiple stars. The Kepler spacecraft has been looking out for such planets, watching for the dip in brightness as a planet crosses in front of one of its stars. Kepler has already found four circumbinary planets, each one alone in its orbit around two stars.
Now Kepler has another so-called Tatooine planet to add to the growing list, but this one’s less lonely. Observations reported by Jerome Orosz (San Diego State University) and his colleagues in Science this week and announced at the International Astronomical Union meeting in Beijing, China show not just one but two planets in stable orbits around a binary star system called Kepler-47.
The inner planet, possibly a rocky one about three times the size of Earth, whizzes around its host stars roughly every 50 days. The outer planet is probably a gas giant slightly larger than Uranus and takes just over 300 days to complete an orbit. Ironically, it’s the gas giant, not the super-Earth, that lies in the stars’ “habitable zone,” the region where an Earth-like planet could have liquid water on its surface.
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