Kepler-16: A Transiting Circumbinary Planet

Carl Sagan Center for the Study of Life in the Universe, SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA.
Science (Impact Factor: 33.61). 09/2011; 333(6049):1602-6. DOI: 10.1126/science.1210923
Source: PubMed


We report the detection of a planet whose orbit surrounds a pair of low-mass
stars. Data from the Kepler spacecraft reveal transits of the planet across
both stars, in addition to the mutual eclipses of the stars, giving precise
constraints on the absolute dimensions of all three bodies. The planet is
comparable to Saturn in mass and size, and is on a nearly circular 229-day
orbit around its two parent stars. The eclipsing stars are 20% and 69% as
massive as the sun, and have an eccentric 41-day orbit. The motions of all
three bodies are confined to within 0.5 degree of a single plane, suggesting
that the planet formed within a circumbinary disk.

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Available from: Jerome A. Orosz
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    • "Lissauer et al., 2011), circumbinary planets (e.g. Sigurdsson et al., 2003; Doyle et al., 2011) and the Solar System defy a single, simple explanation for their formation. After formation, these systems are subjected to internal forces, from planets and smaller bodies, and external forces, such as the singular or repeated local close encounters with individual passing stars, the Galactic tide, tidal tails, molecular clouds, globular clusters or even dark matter substructures. "
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    ABSTRACT: The increasing number and variety of extrasolar planets illustrates the importance of characterizing planetary perturbations. Planetary orbits are typically described by physically intuitive orbital elements. Here, we explicitly express the equations of motion of the unaveraged perturbed two-body problem in terms of planetary orbital elements by using a generalized form of Gauss' equations. We consider a varied set of position and velocity-dependent perturbations, and also derive relevant specific cases of the equations: when they are averaged over fast variables (the "adiabatic" approximation), and in the prograde and retrograde planar cases. In each instance, we delineate the properties of the equations. As brief demonstrations of potential applications, we consider the effect of Galactic tides. We measure the effect on the widest-known exoplanet orbit, Sedna-like objects, and distant scattered disk objects, particularly with regard to where the adiabatic approximation breaks down. The Mathematica code which can help derive the equations is freely available upon request.
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    • "In the former case the planet orbits at such a great distance that the stars are effectively a single point mass. An exception is the recently discovery, Kepler 16b (Doyle et al. 2011). It has the smallest orbital distance yet found for a P-type orbit; just 0.7 AU. "
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    ABSTRACT: More than 800 confirmed exoplanets are currently known. However, the number of exoplanets known in binary star systems is far less. These planets are in wide binaries with stellar orbital periods of decades or longer. The planets can be either circumbinary (P-type) or circumstellar (S-type). Most of the known binaries with planets are S-type systems. The existence of planets in binary star systems tests models of planet formation. In the case of S-type orbits the protoplanetary disk surrounding one star is tidally and thermally perturbed by the companion star. Theoretical studies have indicated that planet formation may be impossible if the stars are closer than 20-100 AU. But Gamma Cep and HD196885 have planets that are at 20 AU. HR 7162 has a planet inside this limit (19 AU). This paper reports the progress of a search for exoplanets with S-type orbits in short-period binary star systems. The selected targets have stellar orbital periods of just a few days. These systems are eclipsing binaries so that exoplanet transits, if planets exist, will be highly likely. Furthermore, the possible range of planetary orbital periods can be predicted. From this it is possible to establish when the orbital phases of all possible planetary period have been sufficiently sampled. So by this technique null detections can establish a lack of planets above a certain size, set by photometric precision. We report the results for 8 binary star systems
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    • "In addition, a dynamical study (Doyle et al. 2011, supporting online material) has indicated that the planetary orbit will undergo cyclic changes in eccentricity up to a value of ~ 0.09 over a period of 2 Myr. If the dynamical evolution of the system were to permit the line of apsides of the binary and that of the planet to coincide, such that the planet could come to opposition at its closest point to the barycentre—when the K star were at binary apoastron—then the distance between the planet and barycentre would be 0.634 AU, and that to the centre of the K star would be reduced to a mere 0.583 AU. "
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    ABSTRACT: We use the circumbinary planetary system Kepler-16b as an example to specify some considerations that may be of interest to astrobiologists regarding the dynamic nature of habitable zones around close double star systems.
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