54 Piscium b

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54 Piscium b
Exoplanet List of exoplanets
Parent star
Star 54 Piscium A
Constellation Pisces
Right ascension (α) 00h 39m 21.806s[1]
Declination (δ) +21° 15′ 01.71″[1]
Apparent magnitude (mV) 5.8
Distance 36.1 ± 0.1[1] ly
(11.06 ± 0.04[1] pc)
Spectral type K0V
Orbital elements
Semi-major axis (a) 0.296±0.017 AU
Eccentricity (e) 0.618±0.051
Orbital period (P) 62.206±0.021 d
Argument of
(ω) 233.3 ± 7.4°
Time of periastron (T0) 2,452,189.83 ± 0.68 JD
Semi-amplitude (K) 16.1±1.2 m/s
Physical characteristics
Minimum mass (m sin i) 0.227 ± 0.023 MJ
(72.1 ± 7.3 M)
Temperature (T) ~404 K (131 °C; 268 °F)
Discovery information
Discovery date January 16, 2002
Discoverer(s) Butler,
Fischer, and
Marcy et al.
Discovery method Radial velocity
Discovery site  United States
Discovery status Confirmed
Other designations
HD 3651 b
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

54 Piscium b (HD 3651 b), occasionally catalogued as 54 Piscium Ab in order to differentiate from the brown dwarf in the system, is an extrasolar planet[2][3] approximately 36 light-years away in the constellation of Pisces. The planet was discovered orbiting the orange dwarf star 54 Piscium. The planet's minimum mass is one fifth that of Jupiter, and it orbits the star in a very eccentric orbit about every two months.


On January 16, 2002, a team of astronomers (led by Geoff Marcy) announced the discovery of an extrasolar planet around 54 Piscium using the radial velocity method,[3] a process utilizes the "wobbling" effect that a star may experience if something is tugging on it, to define the presence of a planetary body. The planet has been estimated to have a mass of only 20 percent that of Jupiter (making the planet around the same size and mass of Saturn).

Orbit and mass[edit]

An artist's impression of the brown dwarf (54 Piscium B) and the planet closer to its sun (54 Piscium b).

The planet orbits its sun at a distance of 0.28 astronomical units (which would be within the orbit of Mercury), which takes approximately 62 days to complete. The planet has a high eccentricity of about 0.63. The highly elliptical orbit, however, suggested that the gravity of an unseen object farther away from the star was pulling the planet outward. The eccentric orbit became clear with the discovery of the brown dwarf within the system.


The orbit of an Earth-like planet would need to be centered within 0.68 AU[4] (around the orbital distance of Venus), which in a Keplerian system means a 240-day orbital period. In a 2006 simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet’s apastron distance, near the 1:2 mean-motion resonance". Also, observation has ruled out Neptune-class or heavier planets with a period of one year or less; which still allows for Earth-sized planets at 0.6 AU or more.[5]

See also[edit]

  • 109 Piscium b - another nearby planet in the constellation of Pisces


  1. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  2. ^ Butler, R. P.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. arXiv:astro-ph/0607493Freely accessible. Bibcode:2006ApJ...646..505B. doi:10.1086/504701. 
  3. ^ a b Fischer, Debra A.; et al. (2003). "A Sub-Saturn Mass Planet Orbiting HD 3651". The Astrophysical Journal. 590 (2): 1081–1087. Bibcode:2003ApJ...590.1081F. doi:10.1086/375027. 
  4. ^ square root of luminosity
  5. ^ Wittenmyer, Robert A.; et al. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal. 134 (3): 1276–1284. arXiv:0706.1962Freely accessible. Bibcode:2007AJ....134.1276W. doi:10.1086/520880. 

External links[edit]

Coordinates: Sky map 00h 39m 21.8s, +21° 15′ 01.7″