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  • Writer's pictureJames Paulson

Circumbinary planet Kepler 16b


About half of all stars in our known universe are part of a binary or multiple star system. This opens a whole new spectrum of possibilities in terms of planetary systems and configurations if those stars can host planets. Astronomers have known for years that there are a great many binary and multiple star systems, made up of all types of star types and configurations. What remained unknown for so long was whether these multiple star systems had planets. It took some time to find an answer, as well as some modern technology and a desire for the truth.


On September 15, 2011, astronomers using data from NASA's Kepler Space Telescope announced the first partial-eclipse-based discovery of a circumbinary planet. The planet, which came to be called Kepler 16b, is about 200 light years from Earth, and lies in the constellation of Cygnus, and it is believed to be a frozen world of rock and gas, about the same mass as Saturn. It orbits two stars that are also circling each other, one about two-thirds the size of our sun, the other about a fifth the size of our sun. Each orbit of the stars by the planet takes 229 days, while the planet orbits the system's center of mass every 225 days; the stars eclipse each other every three weeks or so.


To me, it sounds like an interesting place to raise a family. One would have a continuous sense of the universe beyond. It almost makes me wonder if people on these planets would contemplate whether a planet could exist in a system where there is only one star? Or if they thought intelligent life could arise in a single star system?

Kepler-16b (formally now called Kepler-16 (AB)-b) is officially an extrasolar planet. It is a Saturn mass planet consisting of half gas and half rock and ice. It is orbiting two stars so therefore it is a circumbinary planet.


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Kepler-16b is also unusual in that it falls inside the radius that was thought to be the inner limit for planet formation in a binary star system. According to Sara Seagar, a planetary expert at MIT, it was thought that for a planet to have a stable orbit around such a system, it would need to be at least seven times as far from the stars as the stars are from each other. Kepler-16b's orbit is only about half that distance. Once again, science is using its process to determine and correct its own ideas.

Kepler-16b orbits near the outer edge of the “goldilocks zone”, AKA habitable zone, but it is most probably a gas giant with surface temperatures around −100 to −70 °C (−150 to −94 °F).


The habitable zone of the Kepler-16 system extends from approximately 55 to 106 million kilometers away from the binary system. Kepler-16b, with an orbit of about 104 million kilometers, lies near the outer edge of this habitable zone. Although the chances of life on the gas giant itself are remote, simulations conducted by researchers at the University of Texas have suggest that sometime in the system's history, perturbations from other bodies could have caused an Earth-sized planet from the center of the habitable zone to migrate out of its orbit, allowing Kepler-16b to capture it as its moon. Furthermore, the researchers also considered the possibility of a faraway habitable planet orbiting at about 140 million kilometers away, which could retain the thermal energy needed to keep water liquid through a thick mixture of greenhouse gases including carbon dioxide and methane.


The idea of being from a star system with multiple Sun’s is not as far fetched as it may appear. Your days would be a bit longer and your nights would be a bit shorter, but the idea of a pair of stars eclipsing each other might be quite unique, and the combinations that it offers as well. For part of the year, the stars would appear to trade places with each other, and that well might be what determines the seasons. Either way, it is a neat concept to imagine, and drags our minds to distant places that actually exist but which we will never get to visit except inside of our imagination.



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