16 Cygni Bb

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HD 186427 b
Extrasolar planet List of extrasolar planets
16 Cyg B b rv.pdf
Radial velocity changes over time of 16 Cygni B caused by the orbit of 16 Cygni B b.
Parent star
Star HD 186427
Constellation Cygnus
Right ascension (α) 19h 41m 51.972s[1]
Declination (δ) +50° 31′ 03.1″[1]
Distance 69.2 ± 0.4[1] ly
(21.2 ± 0.1[1] pc)
Spectral type G2.5Vb
Mass (m) 0.97 M
Radius (r) 1.2 R
Temperature (T) 5752 ± 3.5[2] K
Metallicity [Fe/H] 0.09
Age 9.9 Gyr
Orbital elements
Semimajor axis (a) 1.681 ± 0.097 AU
Eccentricity (e) 0.689 ± 0.011[3]
Orbital period (P) 798.5 ± 1.0 d
Inclination (i) 45 or 135[3]°
Argument of
(ω) 83.4 ± 2.1[3]°
Time of periastron (T0) 2,446,549.1 ± 6.6 JD
Semi-amplitude (K) 50.5 ± 1.6 m/s
Physical characteristics
Mass (m) 2.38 ± 0.04[3] MJ
Maximum stellar flux (F⊙max) 4.4
Minimum stellar flux (F⊙min) 0.16
Discovery information
Discovery date 22 October 1996
Discoverer(s) William D. Cochran, Artie P. Hatzes, R. Paul Butler, Geoff Marcy
Discovery method Radial velocity
Discovery site  United States
Discovery status Published
Database references
Extrasolar Planets

16 Cygni Bb or HD 186427 b is an extrasolar planet approximately 69 light-years away in the constellation of Cygnus.[4] The planet was discovered orbiting the sun-like star 16 Cygni B, one of two solar-mass components of the triple star system 16 Cygni. It makes one revolution every 799 days and was the first eccentric Jupiter and planet in a triple star system to be discovered.


In October 1996 the discovery of a planetary-mass companion to the star 16 Cygni B was announced, with a mass at least 1.68 times that of Jupiter. At the time, it had the highest orbital eccentricity of any known extrasolar planet. The discovery was made by measuring the star's radial velocity.

As the inclination of the orbit cannot be directly measured and as no dynamic model of the system was then published, only a lower limit on the mass could then be determined.[3][5]

Orbit and mass[edit]

The orbit of 16 Cygni Bb (black) compared to the planets in the Solar system.
Fictional texture and polygon model render of 16 Cygni Bb (Rendered by Celestia) viewed from a fictional desert moon. Star 16 Cygni A is seen setting in the moon's atmosphere.

Unlike the planets in our solar system, the planet's orbit is highly elliptical, and its distance varies from 0.54 AU at periastron to 2.8 AU at apastron.[6] This high eccentricity may have been caused by tidal interactions in the binary star system, and the planet's orbit may vary chaotically between low and high-eccentricity states over a period of tens of millions of years.[7]

Preliminary astrometric measurements in 2001 suggested the orbit of 16 Cygni Bb may be highly inclined with respect to our line of sight (at around 173°).[8] This would mean the object's mass may be around 14 times that of Jupiter; the dividing line between planets and brown dwarfs is at 13 Jupiter masses. However these measurements were later proved useful only for upper limits.[9]

A mathematical study in 2012 showed that a mass of about 2.4 Jupiter masses would be most stable in this system.[3] This would make the body a true planet. With these tidal effects at that age, a gas giant would be most stable.

Physical characteristics[edit]

Because the planet has only been detected indirectly by measurements of its parent star, properties such as its radius, composition and temperature are unknown.

Habitable zone[edit]

The planet's highly eccentric orbit means the planet would experience extreme seasonal effects. Despite this, simulations suggest that an Earth-like moon would be able to support liquid water at its surface over the course of a year.[10] Due to the eccentric orbit of this massive gas giant, it is unlikely that a habitable planet could survive in this system.[11]

See also[edit]


  1. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry.
  2. ^ Kovtyukh, V. V.; Soubiran, C.; Belik, S. I.; Gorlova, N. I. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics 411 (3): 559–564. arXiv:astro-ph/0308429. Bibcode:2003A&A...411..559K. doi:10.1051/0004-6361:20031378. 
  3. ^ a b c d e f Plávalová, E.; Solovaya, N. A. (2012). "Analysis of the motion of an extrasolar planet in a binary system". arXiv:1212.3843 [astro-ph.EP].
  4. ^ The Discovery of a Planetary Companion to 16 Cygni B, W. D. Cochran, A. P. Hatzes (Univ. Texas), R. P. Butler, G. W. Marcy (SFSU and U. C. Berkeley), (Submitted on 27 Nov 1996)
  5. ^ Butler, R. P.; Marcy, G. W. The Lick Observatory Planet Search. IAU Colloquium No. 161, Capri 1–5 July 1996. p. 331. Bibcode:1997abos.conf..331B. 
  6. ^ Butler, R. P.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701. 
  7. ^ Holman, M.; Touma, J.; Tremaine, S. (1997). "Chaotic variations in the eccentricity of the planet orbiting 16 Cygni B". Nature 386 (6622): 254–256. Bibcode:1997Natur.386..254H. doi:10.1038/386254a0. 
  8. ^ Han, I.; Black, D. C.; Gatewood, G. (2001). "Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions". The Astrophysical Journal Letters 548 (1): L57–L60. Bibcode:2001ApJ...548L..57H. doi:10.1086/318927. 
  9. ^ Pourbaix, D.; Arenou, F. (2001). "Screening the Hipparcos-based astrometric orbits of sub-stellar objects". Astronomy and Astrophysics 372 (3): 935–944. arXiv:astro-ph/0104412. Bibcode:2001A&A...372..935P. doi:10.1051/0004-6361:20010597. 
  10. ^ Williams, D. M.; Pollard, D. (2002). "Earth-like worlds on eccentric orbits: excursions beyond the habitable zone". International Journal of Astrobiology 1 (1): 61–69. Bibcode:2002IJAsB...1...61W. doi:10.1017/S1473550402001064. 
  11. ^ Wittenmyer, R. A.; Endl, M.; Cochran, W. D.; Levison, H. F. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal 134 (3): 1276–1284. arXiv:0706.1962. Bibcode:2007AJ....134.1276W. doi:10.1086/520880. 

External links[edit]

Coordinates: Sky map 19h 41m 51.9720s, +50° 31′ 03.083″