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whiskey in the jar
In September the media were filled with news and illustrations of the “Tatooine planet,” Kepler-16b, which orbits not a single star but a close binary pair. (It was nicknamed for Luke Skywalker’s home world in Star Wars.) Circumbinary planets have been strongly suspected before, but this was a solid confirmation.
Meanwhile, out of the media limelight at the Wyoming exoplanet conference, Bill Welsh (San Diego State University) was presenting convincing evidence for at least three and possibly a dozen other circum-binary planets in Kepler’s field of view. “I would still call these ‘candidates’,” Welsh said, “but I would be extremely surprised if they weren’t real. We will know for sure within just a few months.”
Meanwhile, out of the media limelight at the Wyoming exoplanet conference, Bill Welsh (San Diego State University) was presenting convincing evidence for at least three and possibly a dozen other circum-binary planets in Kepler’s field of view. “I would still call these ‘candidates’,” Welsh said, “but I would be extremely surprised if they weren’t real. We will know for sure within just a few months.”
Kepler-16AB, the “Tatooine” host, is an unresolved, 12th-magnitude speck 200 light-years away in Cygnus. Its A and B components are orange and red dwarfs with 0.69 and 0.20 times the mass of the Sun. Their size ratio is also about 3 to 1. The pair eclipse each other every 41 days as they revolve around their center of mass in a mildly eccentric orbit.
In addition, Kepler found that the system’s light also dips by 1.7% and by 0.1% in a complex timing pattern due to a small third body crossing both stars about every 229 days. Its slight gravitational tugs on the stars show that it has nearly Saturn’s mass. The size of its silhouette reveals that it’s a bit smaller in diameter than Saturn and thus should be 1.4 times denser, suggesting that it’s richer in heavy elements.
Such a system is especially valuable because it enables very accurate determinations of the sizes and masses of all the bodies involved. It may also help unlock mysteries of planet formation. The three eclipsing objects orbit within 0.5° of the same plane. This indicates that they formed at the same time, from the same protoplanetary disk, and haven’t been much disturbed since.
That’s not to say things here aren’t changing. Gravitational interactions in this three-body system are warping the planet’s orbital plane around in a precession cycle. The planet is now just grazing the dim starfrom our viewpoint, but should start missing it altogether in 2014. The planet will also miss the brighter star beginning around 2018. Not until about 2042 will the transits start up again.
The planet orbits only three times farther out than the separation of its two suns; they can appear up to 20° apart in its sky. Astronomers didn’t expect such a system to be stable enough to exist long-term. However, orbital simulations indicate that Kepler-16’s particular intimate arrangement is stable on timescales of at least a few million years.
In addition, Kepler found that the system’s light also dips by 1.7% and by 0.1% in a complex timing pattern due to a small third body crossing both stars about every 229 days. Its slight gravitational tugs on the stars show that it has nearly Saturn’s mass. The size of its silhouette reveals that it’s a bit smaller in diameter than Saturn and thus should be 1.4 times denser, suggesting that it’s richer in heavy elements.
Such a system is especially valuable because it enables very accurate determinations of the sizes and masses of all the bodies involved. It may also help unlock mysteries of planet formation. The three eclipsing objects orbit within 0.5° of the same plane. This indicates that they formed at the same time, from the same protoplanetary disk, and haven’t been much disturbed since.
That’s not to say things here aren’t changing. Gravitational interactions in this three-body system are warping the planet’s orbital plane around in a precession cycle. The planet is now just grazing the dim starfrom our viewpoint, but should start missing it altogether in 2014. The planet will also miss the brighter star beginning around 2018. Not until about 2042 will the transits start up again.
The planet orbits only three times farther out than the separation of its two suns; they can appear up to 20° apart in its sky. Astronomers didn’t expect such a system to be stable enough to exist long-term. However, orbital simulations indicate that Kepler-16’s particular intimate arrangement is stable on timescales of at least a few million years.
SOURCE : SKY & TELESCOPE MAGAZINE DECEMBER 2011
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