16 Cygni Bb

16 Cygni Bb or HD 186427 b is an extrasolar planet approximately 69 light-years away in the constellation of Cygnus.[2] The planet was discovered orbiting the Sun-like star 16 Cygni B, one of two solar-mass (M) components of the triple star system 16 Cygni. It orbits its star once every 799 days and was the first eccentric Jupiter and planet in a double star system to be discovered.

16 Cygni Bb
Discovered byWilliam D. Cochran, Artie P. Hatzes, R. Paul Butler, Geoff Marcy
Discovery site United States
Discovery date22 October 1996
Radial velocity
Orbital characteristics
1.681 ± 0.097 AU (251,500,000 ± 14,500,000 km)
Eccentricity0.689 ± 0.011[1]
798.5 ± 1.0 d
Inclination45 or 135[1]
2,446,549.1 ± 6.6
83.4 ± 2.1[1]
Semi-amplitude50.5 ± 1.6
Physical characteristics
Mass2.38 ± 0.04[1] MJ


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 (MJ). 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.[1][3]


The orbit of 16 Cygni Bb (black) compared to the inner planets in the Solar System.

Unlike the planets in the 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.[4] 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.[5]

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°).[6] This would mean the object's mass may be around 14 MJ; the dividing line between planets and brown dwarfs is at 13 MJ. However these measurements were later proved useful only for upper limits.[7]

Physical characteristicsEdit

Because the planet has only been detected indirectly by measurements of its parent star, properties such as its radius, composition and temperature are unknown. A mathematical study in 2012 showed that a mass of about 2.4 MJ would be most stable in this system.[1] This would make the body a true planet.

The planet's highly eccentric orbit means the planet would experience extreme seasonal effects. Despite this, simulations suggest that an Earth-like moon, should it have formed in an orbit so close to the parent star, would be able to support liquid water at its surface for part of the year.[8]

See alsoEdit


  1. ^ a b c d e f Plávalová, Eva; Solovaya, Nina A. (2013). "Analysis of the motion of an extrasolar planet in a binary system". The Astronomical Journal. 146 (5): 108. arXiv:1212.3843. Bibcode:2013AJ....146..108P. doi:10.1088/0004-6256/146/5/108.
  2. ^ Cochran, William D.; et al. (1997). "The Discovery of a Planetary Companion to 16 Cygni B". The Astrophysical Journal. 483 (1): 457–463. arXiv:astro-ph/9611230. Bibcode:1997ApJ...483..457C. doi:10.1086/304245.
  3. ^ Butler, R. P.; Marcy, G. W. (1997). "The Lick Observatory Planet Search". IAU Colloq. 161: Astronomical and Biochemical Origins and the Search for Life in the Universe: 331. Bibcode:1997abos.conf..331B.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ 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.

External linksEdit

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