We report the discovery of a new Kepler transiting circumbinary planet (CBP). This latest addition to the still-small family of CBPs defies the current trend of known short-period planets orbiting near the stability limit of binary stars. Unlike the previous discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has a very long orbital period (~1100 days) and was at conjunction only twice during the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-1647b is not only the longest-period transiting CBP at the time of writing, but also one of the longest-period transiting planets. With a radius of 1.06+/-0.01 RJup it is also the largest CBP to date. The planet produced three transits in the light-curve of Kepler-1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the times of the stellar eclipses, allowing us to measure its mass to be 1.52+/-0.65 MJup. The planet revolves around an 11-day period eclipsing binary consisting of two Solar-mass stars on a slightly inclined, mildly eccentric (e_bin = 0.16), spin-synchronized orbit. Despite having an orbital period three times longer than Earth's, Kepler-1647b is in the conservative habitable zone of the binary star throughout its orbit.
@article{arxiv.1512.00189,
title = {Kepler-1647b: the largest and longest-period Kepler transiting circumbinary planet},
author = {Veselin B. Kostov and Jerome A. Orosz and William F. Welsh and Laurance R. Doyle and Daniel C. Fabrycky and Nader Haghighipour and Billy Quarles and Donald R. Short and William D. Cochran and Michael Endl and Eric B. Ford and Joao Gregorio and Tobias C. Hinse and Howard Isaacson and Jon M. Jenkins and Eric L. N. Jensen and Stephen Kane and Ilya Kull and David W. Latham and Jack J. Lissauer and Geoffrey W. Marcy and Tsevi Mazeh and Tobias W. A. Muller and Joshua Pepper and Samuel N. Quinn and Darin Ragozzine and Avi Shporer and Jason H. Steffen and Guillermo Torres and Gur Windmiller and William J. Borucki},
journal= {arXiv preprint arXiv:1512.00189},
year = {2016}
}