Binary stars and extrasolar planets
The reason could be that migration might become inefficient near the critical radius, leaving planets just outside this radius. Recently, it has been found that the distribution of the innermost planetary semi-major axes is consistent with a log-uniform distribution, taking into account the selection biases, where closer-in planets can be detected more easily.
Most Kepler eclipsing binaries have periods less than 1 day but the shortest period of a Kepler eclipsing binary hosting a planet is 7. The short-period binaries are unlikely to have formed in such a tight orbit and their lack of planets may be related to the mechanism that removed angular momentum allowing the stars to orbit so closely.
As of June , all but one of the confirmed Kepler circumbinary planets are smaller than Jupiter. This cannot be a selection effect because larger planets are easier to detect. All the Kepler circumbinary planets are either close to or actually in the habitable zone. None of them are terrestrial planets , but large moons of such planets could be habitable. Because of the stellar binarity, the insolation received by the planet will likely be time-varying in a way quite unlike the regular sunlight Earth receives.
Circumbinary planets are generally more likely to transit than planets around a single star. The probability when the planetary orbit overlaps with the stellar binary orbit has been obtained.
A Planet was discovered in , but the binarity of the host star was discovered in HD is a Sun-like star orbited by two objects, one of 17 Mj and one of 2. The classification of HD b as a brown dwarf or "superplanet" is currently unclear. The two objects could have both formed in a protoplanetary disk with the inner one becoming a superplanet, or the outer planet could have formed in a circumbinary disk.
Circumbinary planets are common in many science fiction stories:. From Wikipedia, the free encyclopedia. Habitability of binary star systems. California Institute of Technology. The Astrophysical Journal Letters. Evidence for Early Planet Formation". Monthly Notices of the Royal Astronomical Society.
Science , 16 September Retrieved June 14, Evidence for Disk Warping". Retrieved 5 February Carter, Magali Deleuil, Rodrigo F. Fabrycky, Guillaume Hebrard, Tobias C. Hinse, Tsevi Mazeh, Jerome A. A Transiting Circumbinary Planet". Retrieved 18 January Monthly Notices of the Royal Astronomical Society: A Transiting Circumbinary Multiplanet System". Exoplanet Methods of detecting exoplanets Planetary system.
Accretion Merging stars Nebular hypothesis Planetary migration. Astrometry Direct imaging list Microlensing list Polarimetry Pulsar timing list Radial velocity list Transit method list Transit-timing variation.
Astrobiology Circumstellar habitable zone Earth analog Extraterrestrial liquid water Habitability of natural satellites Superhabitable planet. Exoplanetary systems Host stars Multiplanetary systems Stars with proplyds Exoplanets List of exoplanets Discoveries Extremes Firsts Nearest Largest Most massive Terrestrial candidates Kepler Potentially habitable Discovered exoplanets by year before — Discoveries of exoplanets Search projects.
Retrieved from " https: Planets in binary star systems may be candidates for supporting extraterrestrial life. Habitability of binary star systems is determined by a large number of factors from a variety of sources. This may be partly due to sample bias, as massive and bright stars tend to be in binaries and these are most easily observed and catalogued; a more precise analysis has suggested that the more common fainter stars are usually singular, and that up to two thirds of all stellar systems are therefore solitary.
The separation between stars in a binary may range from less than one astronomical unit AU the average Earth-to-Sun distance to several hundred AU. In latter instances, the gravitational effects will be negligible on a planet orbiting an otherwise suitable star, and habitability potential will not be disrupted unless the orbit is highly eccentric see Nemesis , for example.
In reality, some orbital ranges are impossible for dynamical reasons the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range , whilst other orbits present serious challenges for eventual biospheres because of likely extreme variations in surface temperature during different parts of the orbit.
If the separation is significantly close to the planet's distance, a stable orbit may be impossible. Planets that orbit just one star in a binary pair are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or " circumbinary " orbits.
In non circumbinary planets , if a planet's distance to its primary exceeds about one fifth of the closest approach of the other star, orbital stability is not guaranteed. Theoretical work by Alan Boss at the Carnegie Institution has shown that gas giants can form around stars in binary systems much as they do around solitary stars. One study of Alpha Centauri , the nearest star system to the Sun, suggested that binaries need not be discounted in the search for habitable planets.
The HZ for Centauri A is conservatively estimated at 1. For a circumbinary planet , orbital stability is guaranteed only if the planet's distance from the stars is significantly greater than star-to-star distance. The minimum stable star to circumbinary planet separation is about times the binary star separation, or orbital period about times the binary period. The innermost planets in all the Kepler circumbinary systems have been found orbiting close to this radius.