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Exoplanet List of exoplanets
An artist's rendering of the Kepler-16 system, showing the binary star being orbited by Kepler-16b
Parent star
Star Kepler-16
Constellation Cygnus
Apparent magnitude (mV) 11.5
Mass (m) 0.69 / 0.2026 M
Radius (r) 0.649 / 0.2262 R
Temperature (T) 4450 ± 150 (A) K
Metallicity [Fe/H] −0.3 ± 0.2 (A)
Orbital elements
Epoch BJD 2455212.12316
Semi-major axis (a) 0.7048 ± 0.0011 AU
Eccentricity (e) 0.0069 ± 0.0015
Orbital period (P) 228.776 ± 0.037 d
Inclination (i) 90.0322 ± 0.0023°
Longitude of the node (Ω) 0.003 ± 0.013°
Argument of
(ω) 318 ± 22°
Mean longitude (λ) 106.51 ± 0.32°
Physical characteristics
Mass (m) 0.333 ± 0.015 MJ
Radius (r) 0.7538 ± 0.0025 RJ
Stellar flux (F) ~0.31
Density (ρ) 0.964 ± 0.047 g cm−3
Surface gravity (g) 14.52 ± 0.7 m/s²
Temperature (T) 170–200 K (−103 – −73 °C; −154 – −100 °F)
Discovery information
Discovery date 09.15.2011
Discoverer(s) Laurance Doyle[1]
Discovery method Transit (Kepler Mission)
Other detection methods Radial velocity,
Eclipsing binary timing variations,
Transit timing variations
Discovery status Published
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

Kepler-16b (formally Kepler-16 (AB)-b) is an extrasolar planet. It is a Saturn-mass planet consisting of half gas and half rock and ice,[2] and it orbits a binary star, Kepler-16, with a period of 229 days.[1] "[It] is the first confirmed, unambiguous example of a circumbinary planet – a planet orbiting not one, but two stars," said Josh Carter of the Harvard-Smithsonian Center for Astrophysics, one of the discovery team.[3]

Kepler-16b was discovered using the space observatory aboard NASA's Kepler spacecraft.[4] Scientists were able to detect Kepler-16b using the transit method, when they noticed the dimming of one of the system's stars even when the other was not eclipsing it.[4] Furthermore, duration of transits and timing all the eclipses and transits of Kepler-16b and its stars in the system has allowed for unusually high precision in the calculations of the sizes and masses of objects in the Kepler-16 system.[5] The leader of Kepler-16b's discovery team, Laurance Doyle of the SETI Institute in Mountain View, California, said of this precision, "I believe this is the best-measured planet outside the solar system.".[5] For example, Kepler-16b's radius is known to within 0.3%, better than that of any other known exoplanet (as of September 2011).[6]

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.[5] According to Sara Seager, a planetary expert at the Massachusetts Institute of Technology, 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.[5] Kepler-16b's orbit is only about half that distance.[5]

As seen from Earth, Kepler-16b ceased transiting the dimmer star in 2014, and will stop crossing the second, brighter star in 2018. After that, Kepler-16b will remain undetectable using the transit method until around 2042.[5]

Kepler-16b orbits near the outer edge of the habitable zone,[7] but it is probably a gas giant with surface temperatures around −100 to −70 °C (−150 to −94 °F).


In the announcement paper, the discovery team stated: "Following the convention of Ref. 22,[8] we can denote the third body Kepler-16 (AB)-b, or simply “b” when there is no ambiguity."[1] It is listed as Kepler-16 (AB)-b on the SIMBAD Astronomical Database.[9] The Extrasolar Planets Encyclopaedia lists it as Kepler-16 (AB) b.[10]

The Smithsonian Center has informally referred to Kepler-16b as "Tatooine", a reference to the fictional planet orbiting two suns that is a key setting in the popular Star Wars series.[5] "Again and again we see that the science is stranger and weirder than fiction" said John Knoll, a visual effects supervisor at Industrial Light & Magic, who worked on several of the movies.[5]

Artistic impression of the Kepler-16-system with Kepler-16A in yellow, Kepler-16B in reddish-orange and Kepler-16 (AB)-b in violet.

Potential habitability[edit]

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 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.[11] 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.


  1. ^ a b c Doyle, Laurance R.; Carter, Joshua A.; Fabrycky, Daniel C.; Slawson, Robert W.; Howell, Steve B.; Winn, Joshua N.; Orosz, Jerome A.; Prša, Andrej; Welsh, William F.; et al. (2011). "Kepler-16: A Transiting Circumbinary Planet". Science 333 (6049): 1602–6. arXiv:1109.3432. Bibcode:2011Sci...333.1602D. doi:10.1126/science.1210923. PMID 21921192. 
  2. ^ Drake, Nadia. "On Kepler-16b, shadows come in pairs". Science News. Society for Science & the Public. Retrieved 16 September 2011. 
  3. ^ "From Star Wars to science fact: Tatooine-like planet discovered". Smithsonian Science. The Smithsonian Institution. Retrieved 24 September 2011. 
  4. ^ a b Gold, Scott (2011-09-15). "Scientists find planet orbiting two suns like in 'Star Wars'". Los Angeles Times. Retrieved 16 September 2011. 
  5. ^ a b c d e f g h Overbye, Dennis (2011-09-15). "NASA Detects Planet Dancing With a Pair of Stars". The New York Times. Retrieved 16 September 2011. 
  6. ^ Winn, Joshua N.; Albrecht, Simon; Johnson, John Asher; Torres, Guillermo; Cochran, William D.; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard; Fischer, Debra (2011). "Spin-orbit alignment for the circumbinary planet host Kepler-16 A". arXiv:1109.3198v2. 
  7. ^
  8. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets" 1012: 707. arXiv:1012.0707. Bibcode:2010arXiv1012.0707H. 
  9. ^ Object query: Kepler-16b on the online SIMBAD Astronomical database
  10. ^ Jean Schneider (2011). "Notes for Planet Kepler-16 (AB) b". Extrasolar Planets Encyclopaedia. Retrieved 23 September 2011. 
  11. ^ Jaggard, Victoria (January 9, 2012). ""Tatooine" Planet With Two Suns Could Host Habitable Moon?". National Geographic. 

External links[edit]